# Patterns of invasive ctenophore Mnemiopsis leidyi distribution and variability in different recipient environments of the Eurasian seas: A review

T. A. Shiganova, U. Sommer, J. Javidpour, J. C. Molinero, A. Malej, A. S. Kazmin, M. O. I. Isinibilir, E. Christou, I. Siokou-Frangou, M. Marambio, et al.

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## To cite this version:

T. A. Shiganova, U. Sommer, J. Javidpour, J. C. Molinero, A. Malej, et al. Patterns of invasive ctenophore Mnemiopsis leidyi distribution and variability in different recipient environments of the Eurasian seas: A review. Marine Environmental Research, 2019, pp.104791. 10.1016/j.marenvres.2019.104791. hal-02439853

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# Patterns of invasive ctenophore Mnemiopsis leidyi distribution and variability in different recipient environments of the Eurasian seas

## A review

Shiganova, Tamara; Sommer, Ulrich; Javidpour, Jamileh; Molinero, Juan Carlos; Malej, Alenka; Kazmin, A S; Okyar, Melek Isinibilir; Christou, E; Siokou-Frangou, I; Marambio, Macarena; Fuentes, Veronica; Mirsoyan, Z A; Gülsahin, N; Lombard, Fabien; Lilley, M K S; Angel, Dror; Galil, B S; Bonnet, Delphine; Delpy, Floriane

Published in:

Marine Environmental Research

DOI:

10.1016/j.marenvres.2019.104791

Publication date:

2019

Document version:

Submitted manuscript

Citation for published version (APA):

Shiganova, T., Sommer, U., Javidpour, J., Molinero, J. C., Malej, A., Kazmin, A. S., Okyar, M. I., Christou, E., Siokou-Frangou, I., Marambio, M., Fuentes, V., Mirsoyan, Z. A., Gülsahin, N., Lombard, F., Lilley, M. K. S., Angel, D., Galil, B. S., Bonnet, D., & Delpy, F. (2019). Patterns of invasive ctenophore Mnemiopsis leidyi distribution and variability in different recipient environments of the Eurasian seas: A review. *Marine Environmental Research, 152*, [104791]. https://doi.org/10.1016/j.marenvres.2019.104791

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Patterns of invasive ctenophore *Mnemiopsis leidyi* distribution and variability in different recipient environments of the Eurasian seas: A review

T.A. Shiganova, U. Sommer, J. Javidpour, J.C. Molinero, A. Malej, A.S. Kazmin, M.O.I. Isinibilir, E. Christou, I. Siokou- Frangou, M. Marambio, V. Fuentes, Z.A. Mirsoyan, N. Gülsahin, F. Lombard, M.K.S. Lilley, D.L. Angel, B.S. Galil, D. Bonnet, F. Delpy

PII: S0141-1136(19)30509-4

DOI: https://doi.org/10.1016/j.marenvres.2019.104791

Reference: MERE 104791

To appear in: *Marine Environmental Research*

Received Date: 11 August 2019

Revised Date: 12 September 2019

Accepted Date: 17 September 2019

Please cite this article as: Shiganova, T.A., Sommer, U., Javidpour, J., Molinero, J.C., Malej, A., Kazmin, A.S., Isinibilir, M.O.I., Christou, E., Siokou- Frangou, I., Marambio, M., Fuentes, V., Mirsoyan, Z.A., Gülsahin, N., Lombard, F., Lilley, M.K.S., Angel, D.L., Galil, B.S., Bonnet, D., Delpy, F., Patterns of invasive ctenophore *Mnemiopsis leidyi* distribution and variability in different recipient environments of the Eurasian seas: A review, *Marine Environmental Research* (2019), doi: https://doi.org/10.1016/j.marenvres.2019.104791.

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Patterns of invasive ctenophore *Mnemiopsis leidyi* distribution and variability in different recipient environments of the Eurasian seas: a review

Shiganova T. A.¹*, Sommer U. ², Javidpour J.², Molinero J.C.², Malej A.³, Kazmin A.S.¹, Isinibilir M.O. I.⁴, Christou E.⁵, Siokou- Frangou I.⁵, Marambio M.⁶, Fuentes V.⁶, Mirsoyan Z.A.⁷, Gülsahin N.⁸, Lombard F.⁹, Lilley M.K.S.⁹,¹⁰, Angel D. L.¹¹, Galil B.S.¹², Bonnet D.¹³, and Delpy F.¹⁴

¹Shirshov Institute of Oceanology Russian Academy of Sciences, Moscow, Russia

²GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany

³National Institute of Biology, Marine Biological Station, Piran, Slovenia

⁴Department of Marine Biology, Faculty of Aquatic Sciences, İstanbul University, İstanbul, Turkey

⁵Institute of Oceanography Hellenic Centre for Marine Research, Athens, Greece

⁶Institut de Ciències del Mar, CSIC, Barcelona, Spain

⁷Azov Institute for Fishery, Rostov-on-Don, Russia

⁸Mugla Sitki Kocman University, Faculty of Fisheries, Turkey

⁹Observatoire Océanographique de Villefranche, France

¹⁰College of Life and Environmental Sciences, University of Exeter, London, UK

¹¹University of Haifa, Mt Carmel, Haifa, Israel

¹²Steinhardt Museum of Natural History, Israel National Center for Biodiversity Studies, Tel Aviv University, Tel Aviv, Israel

¹³Laboratoire ECOSYM, UMR 5119, Université Montpellier, Montpellier, France

¹⁴Aix-Marseille Université, Université de Toulon, CNRS/INSU, IRD, MIO UM 110, Mediterranean Institute of Oceanography, 13288 Marseille, France

*Corresponding author: Tamara Shiganova, E-mail: shiganov@ocean.ru

**Abstract**

Harmful invader ctenophore *Mnemiopsis leidyi*'s expansions in the Eurasian Seas, its spatio-temporal population dynamics depending on environmental conditions in recipient habitats have been synthesized.

*M. leidyi* found suitable temperature, salinity and productivity conditions in the temperate and subtropical environments of the semi-enclosed seas, in the coastal areas of open basins and in closed water bodies, where it created autonomous populations. *M. leidyi* changes its phenology depending on seasonal temperature regime in different environments.

We assessed ranges of sea surface temperature, sea surface salinity and sea surface chlorophyll values, sufficient for *M. leidyi* general occurrence and reproduction based on comprehensive long-term datasets, contributed by co-authors. This assessment revealed that there are at least two eco-types (Southern and Northern) in the recipient seas of Eurasia with features specific for their donor areas. The range of thresholds for *M. leidyi* establishment, occurrence and life cycle in both eco-types depends on variability of environmental parameters in their native habitats.

**Key words:** invasive ctenophores; *Mnemiopsis leidyi*; distribution patterns; phenology; native habitats; recipient Eurasian seas
# 1. Introduction

Blooms of gelatinous zooplankton have become frequent due to increasing anthropogenic disturbance of environment such as eutrophication, overfishing, and rising temperature. As a result, in regions that previously supported many trophic levels and had productive fisheries, particularly in coastal waters, estuarine and semi-enclosed seas, simpler ecosystems dominated by gelatinous Cnidaria or Ctenophora now prevail. Trends in gelatinous populations reveal ecosystems where jellies share preys with adult or larval fishes (Shiganova and Bulgakova, 2000; Oguz et al., 2008; Boero, 2013). Strong populations of gelatinous species in native habitats increase the possibility of their spreading to other parts of the World Ocean. Shipping, aquaculture and canals connecting previously separated waters facilitate invasions, where population explosions may occur, leading to disturbance of ecosystem services (Galil et al., 2018; Olenin et al., 2016; Shiganova, 2010). Understanding the reasons that facilitate blooms, dispersal and impact of gelatinous invasive species is crucial to develop long-term management against biodiversity loss and marine ecosystem degradation.

The lobate ctenophore *Mnemiopsis leidyi* A. Agassiz 1865 is native to estuaries and bays along temperate and subtropical coastal waters of North and South America where it occurs at a wide range of temperature and salinity (Harbison et al., 1978; Kremer, 1994; Purcell et al., 2001; Costello et al., 2012, Mianzan, 1999; Oliveira et al., 2016). Since the early 1980s *M. leidyi* has penetrated in new areas with ballast waters due to shipping intensification, global expansion of its routes and basins connectivity extention (Seebens et al., 2019). Factors facilitating *M. leidyi* establishment include climate warming and increasing disturbance of marine environments. In particular, the closed and semi-enclosed seas of Eurasia provide favorable conditions for the establishment of new populations.

Genetic studies have clarified the invasion history of *M. leidyi* in Eurasia. Despite some differences in conclusions, all studies confirm multiple invasions: *M. leidyi* was introduced from the Gulf of México to the Black Sea in ballast waters and subsequently spread throughout Ponto-Caspian basin and the Mediterranean Sea. An influx from USA coastal waters (Narragansett Bay) was the donor of populations in the North and Baltic Seas (Ghabooli et al., 2011; Ghabooli et al., 2013; Reusch et al., 2010; Bolte et al.,
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2013, Bayha *et al.*, 2014). In both regions, *M. leidyi* was introduced from coastal or estuarine areas, with no evidence of an invasion from open Atlantic areas (Bayha *et al.*, 2014).

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Since its invasion in the Black Sea in the early 1980s (Vinogradov *et al.*, 1989), the geographic range of *M. leidyi* expanded over Eurasia by shipping and dispersal, demonstrating its ability to colonize the new recipient ecosystems. As a consequence, a number of observations and monitoring programs have been launched to track its expansion and ecology in new areas. Several review papers summarize the knowledge on invader dispersal and compare its effect on recipient and native habitats, including pattern of distribution, biology, and ecology (Purcell et al., 2001; Shiganova et al., 2001b; Costello et al., 2012). Recent studies in the Mediterranean, Baltic and North seas have provided new insights in some aspects of its biology or were devoted to new records of *M. leidyi* (Oliveira, 2007; Galil *et al.*, 2009; Boero *et al.*, 2009, Fuentes *et al.*, 2009; Javidpour *et al.*, 2006; Faasse & Bayha, 2006; Boersma *et al.*, 2007; Tendal *et al.*, 2007, Malej et al. 2017). In other cases, aspects of its ecophysiology were described for the recipient environments (Fuentes *et al.*, 2010, Javidpour *et al.*, 2009a; Jaspers *et al.*, 2011; Jaspers *et al.*, 2012; Jaspers *et al.*, 2013; Lehtiniemi *et al.*, 2011, Riisgård *et al.*, 2010; Haraldsson *et al.*, 2013, Antajan *et al.*, 2014). Here, we use comprehensive datasets on *M. leidyi* occurrence, to assess the scale of expansion and biogeographic patterns observed throughout the Eurasian seas. In addition, we provide a quantitative assessment of ctenophore life history in the recipient Eurasian ecosystems and compare the results with native North American populations. We review the current understanding of adaptive development strategies of this ctenophore in different, sometimes contrasting, recipient environments.

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The goal of this paper is to show that the ecological plasticity permits the species to adapt to different environments and thus enable the wide distribution of *M. leidyi* in variable recipient ecosystems. Possible phenotypic developments might include different seasonal variability of annual cycle, and changing seasonal patterns of areas of distribution (including source, refugia and sink areas). We suggest that in spite of global existence of one valid species there are at least two ecotypes among introduced and established *M. leidyi* mega-populations: a southern (Black, Caspian, Azov, Marmara, Mediterranean seas and adjacent areas), and a northern (Baltic, North Sea and adjacent Atlantic areas) with ecology specific for their donor area. We
hypothesize that the range of thresholds for *M. leidyi* establishment, occurrence and life cycle in both eco-
types depends on variability of these parameters in their donor areas.

**2. Material and methods**

**2.1. Environmental parameters of recipient areas**

The studied areas are divided into Southern and Northern eco-regions. The Southern recipient seas
include brackish Black, Azov and Caspian seas, the more saline Sea of Marmara, the highly saline
Mediterranean with its adjacent Atlantic areas, and Red Sea. The Northern recipient seas include the
brackish Baltic Sea, the saline North Sea and adjacent Atlantic areas. All these ecosystems undergo the
major structural and functional changes over the recent decades due to the climate and anthropogenic
disturbances. Each of these ecosystems has been invaded by *M. leidyi* (Vinogradov et al., 1989; Studenikina
et al., 1991; Shiganova, 1993; Ivanov et al., 2000; Shiganova et al., 2001a, b; Javidpour et al., 2006; Faasse
& Bayha, 2006; Boersma et al., 2007, Tendal et al., 2007; Oliveira, 2007; Boero et al., 2009; Fuentes et al.,
2009; Galil et al., 2009; Cruz et al., 2018).

The Black, Azov and Caspian Seas (Ponto-Caspian) merged to a single basin several times, most
recently in the Pliocene. They were re-connected by the Volga-Don Canal built in 1952. The Black Sea and
Sea of Azov are also part of the Mediterranean basin, connected via the Bosporus Strait and the Sea of
Marmara. Most of the Black, Azov and Caspian seas are temperate with a continental climate with some
areas freezing in winter. These seas are characterized by relatively low species diversity and high
productivity, in particular the Sea of Azov and the northern Caspian (Table 1). The Caspian Sea is an inland
water body with limnological features (Dumont, 1998; Kosarev, 2006) and specific, mainly autochthonous,
biota (Mordukhai-Boltovskoi, 1960; Kasymov, 1987). Physical geography and bottom topography divide the
Caspian in Northern, Middle, and Southern regions, which have different climatic features.

The Mediterranean Sea is divided into three sub-basins: Western (Alboran, Balearic, Ligurian and
Tyrrhenian Seas), Central (Ionian and Adriatic Seas) and Eastern (Levantine and Aegean Seas) (Table 1)
with different circulation patterns (Iudicone et al., 2003). The Mediterranean shallow shelf, particularly its
bays and lagoons, is subjected to stress from heavily populated drainage areas, intensive shipping,
unsustainable fisheries and a rapidly growing aquaculture. The Mediterranean Sea, being a highly saline and
warm oligotrophic basin, has the highest number of non-native species due to a continuous influx through the Suez Canal (Galil *et al.*, 2018).

The North Sea is an arm of the Atlantic Ocean between Great Britain and north-west Europe. It is relatively shallow basin, featuring a large-scale cyclonic gyre, which influences also the Skagerrak, an outlet to the Atlantic Ocean from the Baltic Sea. The northern part of the North Sea is deeper and reveals seasonal stratification. Hydrodynamics of the North Sea also may be affected by estuaries and fjords (Brown *et al.*, 1999).

The Baltic Sea is a non-tidal basin isolated from the North Sea by geographical (narrow straits) and environmental (low temperature and salinity) barriers (Table 1). It connects with the North Sea via the Danish Straits. Human impacts (overfishing, eutrophication) and blooms of cyanobacteria in the Baltic proper, affecting up to one sixth of the whole sea area particularly in late summer, as well as natural factors (i.e. broad salinity-temperature gradients) have made the Baltic Sea vulnerable to invasion by non-native species (Paavola *et al.*, 2005).

<table><caption>Table 1. Background hydrological and productivity conditions in studied seas</caption><thead><tr><th>Location</th><th>Depth (m), maximum/ mean</th><th>Winter T, (°C)</th><th>Summer T, (°C)</th><th>Salinity</th><th>Chl A (mg m<sup>-3</sup>), (min-max)/ mean</th><th>Zooplankton (mg C m<sup>-3</sup>; mg m<sup>-3</sup>; mg DW m<sup>-3</sup>) (min-max)/mean</th><th>References</th></tr></thead><tbody><tr><td>Black Sea</td><td>2245/1271 Oxygenated layer depth: 60-200</td><td>0-10</td><td>24-27</td><td>12-22.3</td><td>All sea: (0.47-1.62)/0.56±0.01 NW: (1.06 - 1.9)/1.5±0.4</td><td>(0.5-130) mg C m<sup>-3</sup></td><td>Shiganova et al., 2004a</td></tr><tr><td>Sea of Azov without Sivash</td><td>14.5/7</td><td>-0.8 - 1.2</td><td>24-30</td><td>0.1-14</td><td>(2 - >3)</td><td>(67-143) mg C m<sup>-3</sup></td><td>Mirzoyan et al., 2006</td></tr><tr><td>Caspian Sea</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>All</td><td>1025/208</td><td></td><td>22-28</td><td>0.1-13</td><td>3.31±1.1</td><td>(0.32-105) mg C m<sup>-3</sup></td><td>Kosarev, 2006;</td></tr><tr><td>North</td><td>15-20/4.4</td><td>0-11</td><td>25-27</td><td>0.1-11</td><td>6.8± 2.09</td><td>(60.6-105) mg C m<sup>-3</sup></td><td>Shiganova et al., 2004b;</td></tr><tr><td>Middle</td><td>770/192</td><td>5.0-6.0</td><td>24-25</td><td>12.6-13</td><td>2.1± 0.86</td><td>(2.3-19.6) mg C m<sup>-3</sup></td><td>Kopelevich et al., 2014</td></tr><tr><td>South</td><td>1025/345</td><td>10-10.7</td><td>25-30</td><td>12.6-13</td><td>2.4± 1.59</td><td>(5.4-17.8) mg C m<sup>-3</sup></td><td></td></tr><tr><td>Sea of Marmara</td><td>1335</td><td>8-15</td><td>24-29</td><td>18-29</td><td>(1-2.5)</td><td>(1.94-109.2) mg C m<sup>-3</sup></td><td>Isinibilir, 2011</td></tr><tr><td>N. Aegean Sea coastal waters</td><td>300/30</td><td>12-18</td><td>24-27</td><td>33-39</td><td>(0.02-0.5)/0.32</td><td>(2.1-25.6)/6.7 mg C m<sup>-3</sup></td><td>Siokou-Frangou et al., 2010</td></tr><tr><td>S. Aegean Sea Gokava Bay</td><td>350/100</td><td>14.4-17.1</td><td>24-29</td><td>37-39.6</td><td>(0.08-0.7)</td><td>7338 ind.m<sup>-3</sup> (May)<br>3178 ind.m<sup>-3</sup> (Sept.)</td><td>N. Gülsahin, pers.com.</td></tr><tr><td>Levant Basin Israel coast</td><td>4433/1500</td><td>17.5-23</td><td>26-31</td><td>39.3-40</td><td>(0.04 - 0.16)</td><td>(0.5-8.7) mg C m<sup>-3</sup></td><td>Herut et al., 2011</td></tr><tr><td>N. Adriatic Sea</td><td>55/30</td><td>6-10</td><td>24-28</td><td>28-39</td><td>(0.1 - 4)/2</td><td>(1.3-129.3) mg DW m<sup>-3</sup></td><td>Giani et al., 2012; Mozetič, et al., 2012</td></tr><tr><td>NW Mediterranean</td><td>6.5/3.1</td><td>10-12</td><td>25-30</td><td>35-36</td><td>(0.096-1.28)/ 0.29</td><td>No data</td><td>M. Marambio, pers. comm.<br>http://data.nodc.noaa.gov/las/getUI.do</td></tr><tr><td>S. Catalan Coast</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Berre Lagoon, France</td><td>9.5/7</td><td>3.4-16</td><td>15-28.2</td><td>3-35</td><td>(1.5-110)</td><td>(13-357) mg DW m<sup>-3</sup></td><td>Gaudy &amp; Vicas, 1985; Delpy et al.</td></tr></tbody></table>
<table><thead><tr><th></th><th></th><th></th><th></th><th></th><th></th><th></th></tr></thead><tbody><tr><td></td><td></td><td></td><td>Journal Pre-proof</td><td></td><td></td><td>2016.</td></tr><tr><td>Ligurian Sea</td><td>2850/2300</td><td>13-15</td><td>23-26</td><td>37-39</td><td>(0.1-0.8)</td><td>(0.5-25) mg C m<sup>-3</sup></td><td>Berline et al., 2011<br>Vandromme et al., 2011</td></tr><tr><td>Mediterranean all</td><td>5068/1500</td><td>6-17</td><td>17-28.5</td><td>31-39.9</td><td>(0.005-4.16)</td><td>(0.4-34.5) mg C m<sup>-3</sup></td><td></td></tr><tr><td>W. Baltic Sea Kiel Fjord</td><td>23/13</td><td>&lt;1</td><td>18-21</td><td>8-24</td><td>(1.1-9.7)/5.4</td><td>(0.5-230)/130 mg C m<sup>-3</sup></td><td>J. Javidpour, pers. comm.</td></tr><tr><td>Baltic Sea Great Belt Limfjorden</td><td>4.9</td><td>&lt;1</td><td>17-22</td><td>19-24</td><td>(5-27 µg Chl l<sup>-1</sup>)<br>(2-10 µg Chl l<sup>-1</sup>)</td><td>(2.8-8.1) mg C m<sup>-3</sup></td><td>Riisgård &amp; Vicas, 2014</td></tr><tr><td>North Sea</td><td>50-400</td><td>-1-5</td><td>15-21</td><td>32-34.5<br>10-25</td><td>0.22-5.64 (0.83)</td><td>No data</td><td>http://data.nodc.noaa.gov/las/getUI.do</td></tr></tbody></table>

## 2.2. Sampling methods and data sets.

Long-term data sets were mostly collected by similar nets (Table 2) and provide information on seasonal variability and spatial distribution from the beginning of ctenophore establishment up to present time.

<table><caption>Table 2. Sampling locations, methods of collections and data sources</caption><thead><tr><th>Location (time span)</th><th>Number of cruises, stations, observations</th><th>Number of gelatinous plankton samples</th><th>Net type</th><th>Number of zooplankton samples</th><th>Net type</th><th>Data provider</th></tr></thead><tbody><tr><td>Northeastern Black Sea (1992-2017)</td><td>373</td><td>4086</td><td>Net Bogorov-Rass, mesh size 500 µm</td><td>4086</td><td>Juday net, mesh size 200 µm</td><td>Shiganova T.</td></tr><tr><td>Sea of Azov (1989-2015)</td><td>78</td><td>4467</td><td>Net Bogorov-Rass, mesh size 500 µm</td><td>4467</td><td>Juday net, mesh size 200 µm</td><td>Mirsoyan Z.</td></tr><tr><td>Sea of Marmara all (1992)</td><td>1</td><td>76</td><td>Net Bogorov-Rass, mesh size 500 µm</td><td>76</td><td>Juday net, mesh size 200 µm</td><td>Shiganova T.</td></tr><tr><td>Sea of Marmara (2000-2015)</td><td>303</td><td>132</td><td>WP-2, mesh size 200 µm</td><td>272</td><td>WP-2, Mesh size 200 µm</td><td>Isinibilir M.</td></tr><tr><td>Caspian Sea Northern, Middle, Southern (2000-2015)</td><td>56</td><td>460</td><td>Bogorov-Rass net or its smaller modification, mesh size 500 µm</td><td>338</td><td>Juday net, mesh size 200 µm</td><td>Shiganova T.</td></tr><tr><td>NE Aegean Sea, Greece (1999-2014)</td><td>27</td><td>108</td><td>WP-3, mesh size 500 µm</td><td>28</td><td>WP-2, mesh size 200 µm</td><td>Siokoi-Frangou I. Christou E. Shiganova T.</td></tr><tr><td>Aegean Sea, Gokova Bay Turkey (2011-2012)</td><td>336</td><td>266</td><td>WP-2, mesh size 200 µm</td><td>95</td><td>WP-2, mesh size 200 µm</td><td>Gülsahin N.</td></tr><tr><td>Levant basin, Israeli coast (2009-2013)</td><td>Semi-quantitative Sampling</td><td>Visual observations</td><td>NA</td><td>Visual observations</td><td>NA</td><td>Angel D.</td></tr><tr><td>Levant basin, Israeli coast (2012, 2014)</td><td>Semi-quantitative Sampling</td><td>Visual observations</td><td>NA</td><td>45, 17</td><td>NA</td><td>Galil B.</td></tr><tr><td>NW Mediterranean, Catalan coast, Ebro River delta (2010-2012)</td><td>19</td><td>90 + hand collection</td><td>Bongo net, 300-500µm Neustonic net, 100µm</td><td>58</td><td>Bongo net, 300-500µm</td><td>Marambio M. Fuentes V.</td></tr></tbody></table>
<table><tr><td>Berre Lagoon</td><td>8</td><td>136</td><td>Hand collections</td><td>No data</td><td>Hand collections</td><td>Lilley M. Lombard F.</td></tr><tr><td>Berre Lagoon (01.2010-12.2011)</td><td>38</td><td>+ visual observations</td><td></td><td></td><td></td><td>Delpy F.</td></tr><tr><td>Bages-Sigean lagoon (2011)</td><td>11</td><td></td><td></td><td></td><td></td><td>Bonnet D.</td></tr><tr><td>W. Mediterranean, Villefranche-sur-Mer, France coast (2013-2014)</td><td>Daily visual observations for 2 months</td><td>157 &gt;1000 observed</td><td>No data</td><td>No data</td><td>Visual observations</td><td>Lilley M. Lombard F.</td></tr><tr><td>N. Adriatic, Piran coast (2003-2018)</td><td>Irregular/ selective sampling</td><td>No data</td><td>selective sampling & diving observations</td><td>528</td><td>WP2, mesh size 200 µm</td><td>Malej A.</td></tr><tr><td>W. Baltic Sea, Kiel Fjord (2006-2010)</td><td>350</td><td>350</td><td>WP-3, mesh size 1000µm</td><td>104</td><td>WP-2, mesh size 200µm</td><td>Javidpour J.</td></tr></table>

Monthly-mean values of Chl a (mg/m³) based on SeaWiFS satellite measurements (1997-2010) were obtained from the National Oceanic and Atmospheric Association (http://data.nodc.noaa.gov/las/getUI.do).

# 3. Results

## 3.1. Distribution and variability of interannual and seasonal population development in the recipient Eurasian seas

*M. leidyi* is native to the estuaries and coastal waters of the temperate and subtropical parts of North and South America where it occurs in a wide range of temperature, salinity and productivity (Fig. 1) (Kremer, 1994; Purcell et al., 2001; Costello t al., 2012; Mianzan, 1999; Oliveira. at al., 2016).

Interannual variability of sea surface temperature in the Eurasian Seas during 1980-2010 indicates enhanced warming after the late 1990s. Rising temperatures of the surface layer (Fig. 2) led to an increase of warm water species invasions, including *M. leidyi*.

<figure><img src="image_4.png" /></figure>
<figure><img src="image_5.png" /><figcaption>Fig. 2. Variability of SST anomalies in Southern (A) and Northern (B) seas. Arrows indicate the first report of *M. leidyi*. The superimposed time series (dots) show some synchronism of the warming trends in Eurasian Seas since late 1990s.</figcaption></figure>

In the early 1980s *M. leidyi* was introduced into the Black Sea, successfully established there and begun spreading to colonize new areas (Fig. 3). The ctenophore's invasive success has been found in the source-sink dynamics that characterize *M. leidyi* population seasonal distribution. The result of these interactions was a dynamic distribution pattern involving seasonal refugia under unfavorable conditions in the source area. Local current-driven dispersal in the sink area takes place with improving conditions there and growing population expansion around the sink area, while the population declines or disappears when suitable conditions are over. We assess the patterns of *M. leidyi* distribution in all known recipient areas to analyze its seasonal and interannual variability and to identify its potential for continued expansion in new habitats.
<figure><img src="image_6.png" /></figure>

Fig. 3. Chronology of *M. leidyi* invasion and dispersal in the seas of Eurasia. Years indicate first finding in the area (sources: Pereladov, 1988; Vinogradov et al., 1989; Mutlu, 1999; Studenikina et al., 1991; Mirsoyan et al., 2006; Shiganova et al., 2001A; Shiganova, 1993; Shiganova & Malej, 2009; Galil et al., 2009; Boero et al., 2009; Lilley et al., 2014; Fuentes et al., 2010; Marambio et al., 2013; Javidpour et al., 2006; Boersma et al., 2007; Faasse & Bayha, 2006; Hansson, 2006; Oliveira, 2007; Tendal et al., 2007; Van Ginderdeuren et al., 2012; Antajan et al., 2014; Hosia & Falkenhaug, 2013; Delpy et al., 2012; Cruz et al., 2018; Zaghloul et al., in press).

## 3.2. Chronology of *M. leidyi* invasion in the Southern recipient seas and adjacent areas

### 3.2.1. The Black Sea

The Black Sea is a productive basin with high edible mesozooplankton biomass (Table 1), which generally has two seasonal peaks in spring contributed by cold-water Copepoda and late summer contributed by warm-water Copepoda including non-native *Acartia tonsa* in the western more brackish waters and Cladocera (Pasternak, 1993, Shiganova et al. 2014a). Among large gelatinous species there are two native scyphozoan *Aurelia aurita* (L) and *Rhizostoma pulmo* (Macri 1778) and one ctenophore *Pleurobrachia pileus* (O. F. Müller, 1776).

*M. leidyi* was first discovered in the Black Sea in early 1980s (Pereladov, 1988) with ballast waters from the northern Gulf of Mexico (Ghabooli et al., 2011). However, it could successfully establish only in the late 1980s when water temperature increased (Fig. 2) and spread throughout the Black Sea except the central areas of cyclonic gyres and freshened rivers mouths (Fig. 3). Its population reached high value (Fig. 4A) with the highest mean abundance of 304 ind. m⁻³ and biomass of 184 g WW m⁻³ in November 1989 in
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the northeastern areas (Vinogradov et al., 1989) and 326 ind.m⁻³ in the Western Black Sea (Kamburska et al., 2006). Its source regions are the productive coastal waters where it is most abundant and intensively reproduces in warm months. From there due to the horizontal turbulent mixing reproductive aggregations spread in the open sea which is a sink area (Shiganova, 1998).

<figure><img src="image_7.png" /></figure>

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<caption>Fig. 4. Interannual and seasonal variability of *M. leidyi* abundance. A - Black Sea (T. Shiganova's data), B - Sea of Azov (Z. Mirzoyan's data), C - Northern, Middle and Southern Caspian (T. Shiganova's data), D - Sea of Marmara (M. İşinibilir' data). White cells - no data.</caption>

In the 1990s before *Beroe ovata* arrival *M. leidyi* seasonal and interannual abundance significantly changed depending on temperature. After cold winters its population diminished, while after warm winters its abundance remained rather high (Shiganova, 1998). Reproduction was starting in August. The highest abundances, biomass and reproduction rates were recorded in August-September (Fig. 4A), coinciding with temperatures 21-25°C (depending on year and area). That also coincided with the peak of warm-water zooplankton (Shiganova, 1998). In the late autumn, when the thermocline eroded, the entire population sank down to 50 m (video observations by Shiganova, 1993 and Mutlu, 1999) and continued feeding in case water temperature remained above 7-8 °C. When temperature dropped below 5 °C, *M. leidyi* stayed in refugia coastal areas near the bottom at depths of 50-60 m, surviving on energy stored in its mesoglea (Reeve et al.
1989). At these temperatures, its movements slowed down, metabolism decreased, feeding stopped and individuals shrank in size, losing mesoglea (Zaika, 2005; Anninsky et al., 2005).

The *M. leidyi* invasion in the Black Sea disrupted the ecosystem at all trophic levels both bottom up and top down and affected fisheries (Shiganova et al., 2004a). Estimated grazing rates on zooplankton, based only on daily metabolic demands, were 2.7-43.8% of the zooplankton biomass daily in spring after warm winters and 41±67.8% daily in summer. In warm years during the summer peak of *M. leidyi*, its daily grazing demands were greater than the available standing zooplankton stock in the coastal waters (Shiganova et al., 2004a).

However, in 1997 the predatory of *M. leidyi* ctenophore *B. ovata* sensu Mayer 1912 arrived in the Black Sea with ballast waters and the ecosystem began to recover (Shiganova et al. 2001a; 2004a; 2018; Finenko et al., 2003). Appearance of *B. ovata* in the surface layer during the annual reproduction peak of *M. leidyi* had a significant effect on its population, and within two weeks only a few *M. leidyi* individuals remain in the water column (Shiganova et al., 2014a). Therefore, since the arrival of *B. ovata*, *M. leidyi* occurs in sizable amount (i.e. ≥5 ind. m⁻³) only during early and middle summer (Fig. 4A). *M. leidyi* is now almost absent in winter, early spring and late autumn. Impact on zooplankton biomass by *M. leidyi* lasts for 5-13 weeks between late spring and mid-summer, i.e. much shorter than during *M. leidyi* occurrence without *B. ovata* (Shiganova et al., 2014a). In recent years with increasing temperature *M. leidyi* starts to reproduce in May, *B. ovata* appears in water column also in May-June or earlier. Therefore it grazes the *M. leidyi* population before it can reach high abundances. Warmer water temperature in August (> 27 °C since 2012) also reduces the abundance of *M. leidyi* by suppressing intensity of its reproduction (Shiganova et al., 2018).

### 3.1.2. The Sea of Azov

The sea is highly productive with abundant zooplankton (Table 1). There are two seasonal peaks of zooplankton, in spring and summer. In recent years non-native *Acartia tonsa* arrived from the Black Sea and contributes to zooplankton biomass in summer (Mirzoyan et al., 2006). There are no native large gelatinous species in the Sea of Azov. *Aurelia aurita* arrived in the 1970s from the Black Sea when salinity increased and disappeared again when salinity decreased below 11 in the late 1980s (Mirzoyan et al., 2000). Recently, with a new increase of salinity, *A. aurita* appeared again (Mirzoyan, pers. comm.).
The Black Sea is a source of *M. leidyi* for the Sea of Azov, where it enters via the Kerch Strait every spring or early summer with the northward currents associated with the seasonally prevailing southern wind. Since *M. leidyi* cannot survive the winter temperatures of the Sea of Azov, the entire population dies out every autumn at temperatures below 3º C (Studenikina et al., 1991).

After re-introduction the following year, *M. leidyi* gradually occupies the whole sea in June or July. Early introduction (April-May) causes a peak of abundance in July-August at temperatures of 24-26 °C, whilst the peak occurs in September-October when arrival is delayed (until late June) (Mirzoyan et al., 2006). The peak of abundance also depends on zooplankton concentrations in the north-eastern Sea of Azov and on temperature in May-June. If zooplankton concentration (1180-1220 mg.m⁻³) and temperature are high (>25 °C) *M. leidyi* can reach abundance and biomass much higher than in the Black Sea: maximum values were recorded in 1999 and 2002 with 2890 ind. m⁻³ and 119 g wet mass. m⁻³. If zooplankton concentration and temperature are lower (260-470 mg. m⁻³), *M. leidyi* values could be low as those recorded in 1992-1993 with 56 ind.m⁻³ and 56.9 g m⁻³, and in 2003 with 57 ind.m⁻³ and 51.2 g m⁻³ (Fig. 4B) (Mirzoyan et al., 2006). Before 2005 it never spread into the low salinity Taganrog Bay, but since that time it began to spread further, in the eastern part of the bay, surviving at salinities as low as 3.5 (Mirzoyan et al., 2006), probably due to gradual adaptation. During recent years salinity began to increase again. A particular increase was recorded in last years since 2013 (up to 12.92-14.13 in the sea and up to 9 in Taganrog Bay). Therefore, *M. leidyi* can penetrate now throughout the whole sea and most of the bay (Mirzoyan data).

*M. leidyi* impact on the Sea of Azov ecosystem has been stronger than in the Black Sea because of the small shallow sea which did not provide potential prey any refugia. Most trophic levels are the potential food, including fish eggs, fish larvae and larvae of zoobenthic species (Mirsoyan et al., 2006; Nadolinsky, 2006, Rogov et al., 2000; Frolenko, 2006).

Arrival time of *M. leidyi* also affects its grazing rate in the Sea of Azov. Late colonization (late June) means that its daily food demands comprise only 20 % d⁻¹ of the available prey biomass during first month, but by August during the peak of *M. leidyi* when prey concentration has already been grazed down, food demand comprises up to 100% d⁻¹ of available zooplankton. Early colonization implies greater demands in zooplankton, amounting to about 100% d⁻¹ already in July, and its estimated daily demands are in excess of
available zooplankton biomass from July or August. *M. leidyi* continues its development under food deficit (Shiganova et al., 2001a).

*B. ovata* first arrived in the Sea of Azov from the Black Sea in 1999 (Shiganova et al., 2001b). Its seasonal pattern of penetration is similar to that of *M. leidyi*, but it arrives only by the end of summer or early autumn, depending on its development in the Black Sea. *B. ovata* gradually occupies the Sea of Azov. Therefore, the effect of recovery of the ecosystem is much lower than in the Black Sea (Mirsoyan et al., 2006).

### 3.2.3. Caspian Sea

The Caspian Sea is a productive closed basin. The seasonal zooplankton stock increases in April, dominated by non-native species *Acartia tonsa*, *Pleopis polyphemoides* and larvae of *Amphibalanus improvisus* introduced from the Black Sea. *Acartia tonsa* replaced native zooplankton species, in particular *Eurytemora grimmi*, and became dominant in all regions of the Caspian within a few years of introduction (Shiganova et al., 2004b).

*M. leidyi* and *Aurelia aurita* were introduced with ballast waters from the Black Sea to the Middle Caspian in 1999 (Ivanov et al., 2000). *M. leidyi* has expanded even faster in the Caspian than in the Black Sea (Shiganova et al., 2004b). Long-term observations indicate its continuous presence in the Southern Caspian Sea where temperature is 7.4-15.0 °C in winter (Shiganova et al., 2004b; Roohi et al., 2010; Bagheri et al., 2012) and salinity is 12.6-13. Its population size is primarily determined by temperature in the previous winter and winter zooplankton concentrations in the Southern Caspian (Shiganova et al., 2004; Roohi et al., 2010). With spring warming and zooplankton development *M. leidyi* intensity of reproduction and growth accselerates, and increased total population in May or earlier during last years starts to spread northward. The Middle and Northern Caspian are the sink areas where *M. leidyi* lives, grows and reproduces only during the warm seasons. Considering that northward Ekman transport velocity along the eastern coast of the Caspian Sea is 10-30 cm/s (Dobrovolskii & Zalogin, 1982), we can roughly estimate the time required for *M. leidyi* to disperse from the southernmost area due to current advection. So, it takes from 16 to 46 days depending on wind-driven velocity to reach the Middle Caspian from the south (about 400 km) and 12-34 days to be carried from the Middle to the Northern Caspian (about 300 km). The whole way from the south
to the north takes from 28 to 80 days depending on the current velocity. It means that *M. leidyi* could reach the Northern Caspian during the optimal season for creating reproductive population.

When *M. leidyi* first colonized the Southern Caspian Sea, it reached population sizes up to 500 ind. m⁻³ during the peak of development in August-October 2001 (Shiganova et al., 2004b). Its abundances reached 302 ind. m⁻³ in the Middle Caspian in 2008 and 327 and 259 ind. m⁻³ in August and September 2009 respectively in the North-Western Caspian Sea (Fig. 4C). Meanwhile, in the Southern Caspian abundance became lower since 2012. This shift in a peak of abundance from the South to the Middle and Northern Caspian probably results from an earlier seasonal warming in recent years (Shiganova et al., in press), which facilitates earlier northward dispersal. Peaks of abundance occur in August-October in the Middle Caspian and in August- September in the Northern Caspian at 25-26 °C. The salinity tolerance of *M. leidyi* has also changed. Until 2009 it could only live at salinities >4.0 and reproduce at salinities >6, but since 2009 *M. leidyi* has been found in an area with salinities of 3.5 (Shiganova, 2011). In addition, it could not survive in the north-eastern Caspian with low zooplankton biomass and high concentration of particulate organic matter (Shiganova et al., 2003), but now it is recorded in this area since 2010. *M. leidyi* is most abundant in the upper layer above the seasonal thermocline, although in coastal areas it may occur in the entire water column. Larger individuals are usually found deeper (Shiganova et al., 2003; Bagheri et al., 2012). In the deep waters of the Middle Caspian some individuals are found below the thermocline at 25-50 m (Kamakin et al., 2010).

Impacts on the Caspian ecosystem were observed for all trophic levels including the commercially important small pelagic fishes as anchovy *Clupeonella engrauliformes* and big-eye kilkas *C. grimmi* and their consumers, piscovorous fishes including sturgeons, and seal (Shiganova et al., 2004b; Shiganova, 2011). The estimated daily food demands of *M. leidyi* in the Caspian coastal waters of Iran during its peak comprises about 100% d⁻¹ of prey biomass from July to the end of October (Shiganova estimation). In winter and spring, estimated food demands range from 12 to 29% d⁻¹.

In contrast to the Black Sea, *B. ovata* has not been recorded in the Caspian Sea and unrestricted *M. leidyi* blooms continue every year. Thus, ecosystem impacts within the Caspian, including biodiversity loss and in fishery landings reductions are expected to keep increasing.
The Sea of Marmara that connects the Black Sea to the Aegean Sea is a productive basin, particularly in the bays (Table 1). *Acartia clausi* and *Penilia avirostris* are the main mesozooplankton species, the non-native *Acartia tonsa* also occurs but in small numbers. The most abundant native macrogelatinous species are *Aurelia aurita* and *Rhizostoma pulmo*. The former often is accounting for 55% of the total gelatinous zooplankton (Isinibilir et al., 2015).

*M. leidyi* arrived from the Black Sea with the upper Bosporus current, probably when it spread throughout the Black Sea in 1988 (Fig. 3). However, it was recorded and described only in October 1992 (Shiganova, 1993). Subsequently it occurred throughout the year in the upper layer of the Sea of Marmara prior to the arrival of *B. ovata* with a peak of abundance and reproduction in the summer-early autumn (Fig.4D). *M. leidyi* abundance ranged from 1.62 ind. m⁻³ to 27 ind. m⁻³ (Shiganova, 1993; Kıdeys & Niermann, 1994; Isinibilir & Tarkan, 2001; Isinibilir et al., 2004). Although it may reproduce in the whole Sea of Marmara, the highest rates were recorded in the bays, particularly in the highly polluted Izmir Bay, peaking in August-September (Isinibilir, 2012). This area probably serves as a source for the *M. leidyi* population in the Sea of Marmara.

*B. ovata* spread also from the Black Sea and first was found near the Bosporus in 1999 (Tarkan et al., 2000). Its biomass ranged within 6-35 g.m⁻³ during *M. leidyi* blooms. Pattern of interactions of the two ctenophores are similar to the Black Sea, where *B. ovata* appears in the water column when *M. leidyi* reaches its seasonal peak (Isinibilir et al., 2015).

*M. leidyi* affected the whole ecosystem of the Sea of Marmara (Isinibilir, 2012). However, after the appearance of *B. ovata* in last years (2014-2015), mean abundances of *M. leidyi* (Fig 4D) and *B. ovata* were very low in the whole sea. Thereby *B. ovata* effectively controls *M. leidyi* population in the Sea of Marmara and, when it declines *M. leidyi* seasonal abundance, *B. ovata* almost disappears from water column (Isinibilir et al., 2015).

3.2.5. The Aegean Sea
The Aegean Sea is oligotrophic, with zooplankton abundance ranging from 1.7 to 438 ind. m⁻³ and wet biomass from 1 to 59 mg. m⁻³ (Table 1). The high values are found in coastal embayments and bays, with the maximum in Saronikos Gulf (Siokou-Frangou et al., 2004).

### 3.2.5.1. Northern Aegean Sea

The Black Sea provided a source of *M. leidyi* for the northern Aegean Sea via the Sea of Marmara. In addition, *M. leidyi* was introduced, probably with ballast waters, into the Saronikos and Elefsis Gulfs in 1990 (Shiganova et al., 2004c). During 1991-1998 *M. leidyi* abundance was low 0.05-3 ind. m⁻² in the areas, influenced by the Dardanelles Strait (Shiganova et al., 2001a). *M. leidyi* was also recorded in the coastal waters of Gokceada Island (north-eastern Aegean Sea), influenced by the Black Sea currents. Here its values were also low with maximum of 8.3 ind.100 m⁻³-28 g.100 m⁻³, probably due to oligotrophic conditions with low zooplankton biomass (Shiganova et al., 2004c). Therefore, the northern Aegean Sea was considered as a sink area for *M. leidyi* when it first occurred in the areas influenced by outflow of Black Sea water. No impact of *M. leidyi* on the mesozooplankton was detected during first years after colonization, probably due to its low abundance (Shiganova et al. 2001a). *M. leidyi* development and reproduction peaked in spring and early summer, ceasing in the hot summer months (Shiganova et al., 2004c). After 2002, *M. leidyi* abundance began to increase (Siapatis at al., 2010), which was perceived as an evidence for a self-sustaining population establishment. The main reason was probably the increasing zooplankton biomass prey associated with warming (Siokoi-Frangou et al., 2010). *M. leidyi* reached higher abundances in bays and lagoons of the northern Aegean Sea, which probably became source areas for the subsequent northern Aegean population. Highest abundances were recorded in Thermaikos and Strymonikos Gulfs influenced by high river runoffs with reduced salinity and terrigenous nutrient input (Siapatis et al., 2010). Recently (2014-2015) *M. leidyi* is regularly found almost throughout the year with June peaks in a semi-enclosed Maliakos Gulf (Christou unpublished data), which is an evidence of a self-sustaining population there. Thus, during last decade *M. leidyi* have established populations in the bays and coastal waters of the Northern Aegean Sea providing a potential source for other Mediterranean areas.

In the northern Aegean Sea, two *B. ovata* individuals were collected from swarms of *M. leidyi* in the northern Evvoikos Gulf in November 2004 (Shiganova et al., 2007). *B. ovata* has not been observed to
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impact *M. leidyi* populations in the region, probably due to low concentrations of *M. leidyi* or a lack of
observations.

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### 3.2.5.2. The southern Aegean Sea

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*M. leidyi* was first observed along the Turkish coast of the southern Aegean Sea in 1992-1993, when a few ctenophores (2 ind.100 m⁻³) were found off Kusadasi (Kideys and Niermann, 1994). Gökova Bay between the Aegean and Levantine seas is likely to be a separate sink of *M. leidyi* population that originated in the northern Aegean Sea (Gülşahin, 2013; Gülşahin and Tarkan, 2014). In 2011-2012 within Gökova Bay,

<figure><img src="image_8.png" /><figcaption>B Levantine Sea</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>C Ligurian Sea</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>D Catalan Coast</figcaption></figure>

<figure><img src="image_11.png" /></figure>

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Fig. 5. Seasonal and interannual variability of *M. leidyi* abundance in the Mediterranean areas: A - Aegean Sea (N. Gülşahin data); B - Levantine Sea (D. Angel data); C - Villefranche coast, Ligurian Sea (F. Lombard, M. Lilley data); D - Catalan Coast (M. Marambio data). White cells - no data.

*M. leidyi* was studied in several small embayments Marmaris, Bodrum and Fethye, where salinity is 36.45-39.5, winter temperatures are 14.3-17.4 °C and summer (July-August) temperatures 24.5-29.0 °C and low productivity predominates (Table 1; Fig. 5A) (Gülsahin and Tarkan, 2014). Zooplankton reaches peak in May and September with the abundance up to 7338 ind.m⁻³ and 3178 ind. m⁻³ respectively (Table 1). *M. leidyi* appears in March - April and its abundance increases in May at temperatures 23.43-26°C, peaking in late spring and autumn every year with the exact timing depending on location, when temperatures are not higher than 26.5°C (or 18.5°C in November) (Fig. 5A). Maximal biomass of 39.3 g. m⁻³ was observed in Gökova Bay in October 2012, which was facilitated by seasonal peaks of zooplankton (Gülşahin, 2013).
*Beroe mitrata* (Moser, 1907) (identification by T. Shiganova), native to the Mediterranean, probably arrived in Gökova Bay from the northern Aegean Sea with the currents from the north and it is regularly observed in Gökova Bay and several sub-bays. Abundance of *Beroe mitrata* depends on the concentration of *M. leidyi* with peaks at the same time or one month later. In general, the distribution of *M. leidyi* is limited by zooplankton biomass and the distribution of *Beroe mitrata* (Gülşahin, 2013).

### 3.2.6. Levantine Sea

The Levantine Sea is ultra-oligotrophic, with high salinity and temperature in summer (Table 1). *M. leidyi* was first found in the Mersin Bay in spring 1992 (Kideys and Niermann, 1994) and near Latakia in October 1993 (Shiganova, 1997). Since both locations were in the vicinity of ports, and population did not exist after the first findings, it is reasonable to assume that *M. leidyi* had been introduced with ballast water (Shiganova et al., 2001b). In 2009 large swarms (Fig. 5 B) were observed along the Israeli Mediterranean coast up to a depth of 20 m and inside the ports (Galil et al., 2009). In 2009-2013 *M. leidyi* was regularly observed along the Israeli coast (pers. obs. D. Angel, B. Galil) from late winter to early summer (May-June or, in some years, July), in large swarms. *M. leidyi*'s abundance was relatively low with 1.7-3 ind.m⁻³; however, in winter 2012 its mean abundance rose to 6.9 ind. m⁻³ and maximum abundance reached 10 ind.m⁻³ (Fig 5B). As a rule, *M. leidyi* was absent during August-October due to high temperature (Table 1), before re-appearing in November-December with low abundances (0. 75-1.5 ind.m⁻³) (Fig. 5B). In 2014, *M. leidyi* abundance significantly increased (pers. obs. B. Galil). *M. leidyi* has obviously established a self-sustaining population off the Israeli coast with a definite seasonality, its swarms commonly coinciding with the spring zooplankton peak. It might reduce the local zooplankton stock and moderate the size of the early summer swarms of the equally voracious invasive scyphozoan *Rhopilema nomadica* Galil, 1990 (Galil, 2007). Reproduction rates were not studied but probably occur during peak of abundance in spring and autumn.

*B. ovata* sensu Mayer was first recorded along the Mediterranean coast of Israel outside the port of Ashdod in June 2011. Like *M. leidyi*, it may have been transported to Israel with ballast waters from the Black Sea (Galil et al., 2009, 2011). Following the swarming of *M. leidyi* in 2009, and to a lesser degree in 2011-2014, *B. ovata* established a local population, though it remained unrecorded until summer 2011 (Galil
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et al., 2011). This species has been regularly collected in winter-spring and late autumn from 2009 and up to 2017 (Galil obs.). *B.cucumis* sensu Mayer was recorded in December 2011, January and December 2012, and February, April and May 2013 (Galil and Gevili, 2013). Thus, both the invasive *B. ovata* and the Mediterranean *Beroe spp.* appeared in swarms of *M. leidyi*, and preyed on it (Galil et al., 2011; Galil and Gevili, 2013). Identification of both species *Beroe* off the Israeli coast is confirmed by genetic analyses (Ghabooli and Shiganova identification).

### 3.2.7. Adriatic Sea

The northern Adriatic is the northernmost area of the Mediterranean Sea, and strongly influenced by rivers discharge. It is one of the most productive regions of the Mediterranean Sea (Harding et al., 1999), although Trieste Gulf is moderately eutrophic (Table 1) (Malej et al., 1995). Mean mesozooplankton dry mass was around 20 mg m⁻³ in 1989-2002, decreasing to < 10 mg m⁻³ in 2003-2010 (Mozetič et al., 2012) (Table 1).

In October 2005, a swarm of *M. leidyi* was recorded in the shallow (depths < 30 m) Gulf of Trieste, in the northernmost part of the Adriatic Sea, together with native *B. cucumis* sensu Mayer, *B. forskalii* Chun and non-native *B. ovata* from the Black Sea. Ballast waters from the Black Sea provided the source for both *B. ovata* and *M. leidyi*, through regular shipping between the port in Koper and various Black Sea ports (Shiganova and Malej, 2009). In spite of monitoring, *M. leidyi* was not observed in the middle and southern Adriatic Sea, supporting the hypothesis of the ballast waters was the introduction vector in the Gulf of Trieste. Continuous observations during the following years proofed that *M. leidyi* had not built a population in the northern Adriatic despite favorable environmental and trophic conditions. We suggest that the presence of two native and one non-native predatory *Beroe* species prevented establishment of *M. leidyi* after its first arrival. In addition, low propagule pressure was probably also important. This 'natural experiment' suggests that presence of native predators can control *M. leidyi*.

In July-December 2016 large-scale blooms of *M. leidyi* were observed in different locations in the northern Adriatic, at temperatures 13-29 °C and salinities 11-38. Blooms were recorded in the coastal waters near Pula, Rovinj, in the Gulf of Trieste, in Marano-Grado lagoon, Venice lagoon and lagoons in the Po delta, Veneto-Emilia Romagna-Marche regions and offshore waters along a transect from Rovinj. In
addition, in 2016 *M. leidyi* was recorded in the south Adriatic lagoons Lesina and Varano, where they were introduced via artificial tidal canals. Each bloom was composed of individuals of variable sizes and presence of cydippid larvae and juveniles (most numerous in autumn) indicating successful reproduction. Large individuals showed morphological characteristics typical for the other Mediterranean *M. leidyi* (Malej et al., 2017). The vector of arrival is not clear yet but most probable could be ballast waters again.

During 2017 *M. leidyi* was present in the open northern Adriatic from April and was very abundant in summer-early autumn, while in late autumn its abundance dropped (Pagliaga, pers. comm.). In the Gulf of Trieste *M. leidyi* occurred in low abundances in June, in very high abundance in summer, and occured till November (Kogovšek, pers. com.). It was also detected in the Neretva channel in the eastern part of the southern Adriatic although only sporadically and with few individuals (Lučić, pers. comm.). In October 2017 *M. leidyi* was very abundant in lagoons: Lesina with abundance of 80.7±47.8 ind. m⁻³ and in Varano 94.6±129.8 ind. m⁻³. Its maximal abundance was recorded in the western site of the Varano Lagoon 168.9±167.1 ind. m⁻³, while the minimum in the eastern site (20.4±24.4 ind. m⁻³). Thus, *M. leidyi* expanded to the southern Adriatic Sea, establishing populations in productive lagoons.

In 2018 *M. leidyi* was observed in all the previously mentioned Adriatic locations and spread further. It was also recorded by fishermen in large numbers in the lagoon of Grado (V. Tirelli, pers. comm.).

### 3.2.8. Italian coastal areas of the Ligurian, Tyrrhenian Sea and Ionian Seas

In May-June 2009 the first records of *M. leidyi* were made in the Ligurian, Tyrrhenian and one record in the Ionian Seas of Italy (Boero et al., 2009). The large distribution area of *M. leidyi* and high abundance suggest that the species invaded or disperced in this area during the summer 2009. Ctenophores were recorded during observations in the framework of the CIESM Jellywatch campaign in the summer 2009. *M. leidyi* was observed in the area continuously throughout the summer and declined in late autumn. When the swarms started to dissolve, numerous specimens of the fish *Sarpa salpa* (L., 1758) were seen to feed upon the spent ctenophores (Boero et al., 2009). That was first large-scale occurrence *M. leidyi* in the western Mediterranean. Its wide expansion was probably facilitated by local currents, but ballast waters as a vector is also possible.
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There were no further observations in those areas until October 2015, when, during a survey campaign on fishing of European eel in Sardinia, a massive bloom of *M. leidyi* was observed in the eutrophic S'Ena Arrubia Lagoon (Diciotti et al., 2016). Subsequent sampling at three stations in the lagoon was conducted with a fyke net in order to estimate the abundance of *M. leidyi* and to consider its impact on fishing. The abundance, 2.83 ind. m⁻³ consisted of small adults (18-62 mm total length). The high number of *M. leidyi* (6837 individuals per fyke net) damaged fishing operations, reducing catches and affecting the performance of fishing gears. Most probably a separate *M. leidyi* population had established in Arrubia Lagoon.

From June to October 2017 *M. leidyi* was first reported in the Fiora River (Latium, Italy) (Macali & Tiralongo, 2018). Environmental parameters were T = 28.9 °C; pH=6.74; salinity = 1.85 at 1 m depth; flow = 0.44 m/sec; average depth = 1, 75 m. DNA analysis, with the use of the COI mitochondrial marker (see Ghabooli et al., 2013) confirmed its identification. It seems that the establishment of a self-sustained population of the *M. leidyi* in Fiora River is not possible due to low salinity. However, the perspective of high numbers of *M. leidyi* occurrence during the dry season may pose concerns about its future impacts on freshwater species (Macali & Tiralongo, 2018).

### 3.2.9. Ligurian Sea (Villefranche coast)

In April-May 2013 *M. leidyi* was first recorded in the coastal waters of Villefranche-sur-Mer in abundance up to 16.7 ind.m⁻³ and in Port of Monaco on the French Riviera, southern France but for only six weeks in April-May, and for only two weeks at high abundance when temperature was 17 °C and salinity 39 (Fig 5C) (Lilley, Lombard and Shiganova observation). Individuals were predominantly large (mean 8.5 cm, range 1.6-12 cm total length, mean wet weight 26.8 g, maximum wet mass 80 g). Nevertheless, juvenile individuals and a few cydippid larvae were also found, suggesting local reproduction. Adult individuals produced egg strings and reproduced in the laboratory. Appearance of *M. leidyi* in these waters might be explained by current transport. The southeastern coast of France is influenced by the Northern, Ligurian or Liguro-Provençal currents. These currents have been shown to transport zooplankton around the western Mediterranean basin (Qiu et al. 2010), including gelatinous zooplankton, with localized wind events providing onshore transport (Berline et al. 2013). The currents may also have been responsible for the wide
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distribution of *M. leidyi* between the coasts of Italy and Spain in 2009 (Boero et al. 2009; Fuentes et al. 2010). In 2014-2015 *M. leidyi* was regularly recorded in spring and autumn (visual counting during observation by F. Lombard) (Fig. 5C) during the zooplankton bloom, but was absent during the highest summer temperatures where the sea surface reaches 27 °C in the Ligurian coast. We concluded that *M. leidyi* had become established in the French Riviera but its source area is not known yet.

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Among predators, high densities of *Pelagia noctiluca* were observed along French Riviera 10-30 km offshore during an overnight survey on Apr 17, 2013 prior to the bloom of *M. leidyi* and their considerable numbers were also observed in the Bay of Villefranche. *Pelagia noctiluca* is known to prey on *M. leidyi* (Tilves et al., 2013) and occurs year-round close to the study area, being driven off-shore by favorable winds and a near-shore current (Ferraris et al., 2012; Berline et al., 2013). During *M. leidyi* occurrence, both off- and in-shore, high abundance of *P. noctiluca* was observed in the same area and it is likely that *P. noctiluca* contributed to a rapid decrease in the ctenophore population.

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The native *Beroe cucumis* sensu Mayer was recorded simultaneously with *M. leidyi* in March-April 2015 (F. Lombard observation).

### 3.2.10. Lagoons of French Mediterranean coast

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Along the French Mediterranean coast, *M. leidyi* was first observed in Berre (D. Thibault, observation) and Bages-Sigean lagoons (D. Bonnet observation) in 2005. Later it was found in Le Grec in 2010 (D. Banaru observation), in Biguglia and Urbino (Corsica) in 2012 (S. Etourneau observation).

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The first finding in 2005 was most probably introduction with ballast waters and it was the first record of *M. leidyi* in the Western Mediterranean. Genetic analyses have shown that it could be a direct introduction from North America (Ghabooli et al., 2013).

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Berre and Bages-Sigean lagoons are semi-enclosed, shallow basins with temperature and salinity variations linked to anthropogenic freshwater inputs. *M. leidyi* successfully established self-sustaining populations in the Berre and Bages-Sigean Lagoons (Fig. 6 A, B).
A Berre Lagoon

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /></figure>

B Bages Sigean Lagoon

<figure><img src="image_14.png" /></figure>

Fig. 6. Seasonal and interannual distribution of *M. leidyi* in French Lagoons: A- Berre lagoon; B - Bages Sigean lagoon. White cells –no data.

**Berre lagoon**, northwest of Marseille is among the largest coastal lagoons in Europe (155 km², ~7 m deep) (Delpy et al., 2016). It has been under intense anthropogenic pressure for several decades. The massive urbanisation of the surrounding area (1973-1990) and main freshwater inflow from the man-made Durance river bypass channel supplying hydroelectric power plant results in a lower salinity. At that time zooplankton was mainly represented by non-native *Acartia tonsa* and *Brachionus plicatilis*. In 2006 legislation was passed restricting the number of freshwater releases and with increasing salinity the zooplankton became more diverse in 2008-2011. *A. tonsa* is still present, but less abundant, while the native *Aurelia aurita* became a common species in the lagoon (Delpy et al., 2012). In Berre lagoon, *M. leidyi* was present all year around during observations in 2010 and 2011 with small size individuals in low abundance (0.1 ± 0.2 ind.m⁻³) in winter, which were probably shrunken adults because of low temperature (5-7 °C). Small size adults (oral-aboral lengths of (1-2.5 cm) were also present from January to March and from April to June, with individuals in a wider range of sizes (1-6 cm). In the warmest months (August and September) followed marked increase of abundance (7.5 ± 6.0 ind.m⁻³). In autumn (October-November), when the population was mainly composed of small individuals (1.0-3.0 cm), abundance decreases to 3.9±0.2 ind.m⁻³ (Delpy et al., 2016). Based on the size classes it is assumed that reproduction and growth of *M. leidyi* occurred in spring, summer and early autumn (Fig. 6A).

**Bages-Sigean lagoon** is the smallest (37 km²) and shallowest (2.0 m average depth) of these lagoons. In the northern part, it is supplied by freshwater from small rivers and the Robine Canal. The southern part of the lagoon is connected to the Mediterranean Sea by a single channel in Port la-Nouvelle. In Bages-Sigean Lagoon during surveys *M. leidyi* was observed in August and September 2010 (63.5 ± 59.3 ind. m⁻³), and in August - November 2011 (6.1 ± 13.4 ind. m⁻³) (Fig. 6B). Its abundance was up to 50 times higher
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than in the Berre lagoon (Fig. 6B). Maximum abundance was recorded in August 2010 (113.9±11.5 ind. m⁻³) reducing to 20.1 ± 23.0 ind. m⁻³ in August-October 2011 (20.1 ± 23.0 ind. m⁻³). There were no samplings in winter and spring 2010-2011. Seasonal variations of its abundances observed in both lagoons could be associated with environmental conditions such as salinity and biological production related to brackish and eutrophic waters (Delpy et al., 2016).

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In Bages-Sigean lagoon, *M. leidyi* smaller individuals (1-3 cm) were recorded in August, September and November (Delpy et al., 2016). This indicates that reproduction probably occurs in August, September and continues in November.

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Few predators have been recorded in the lagoons. *B. ovata* was recorded in Berre lagoon but with a few individuals. It was observed for the first time in October 2012 (identification by T. Shiganova); its abundance was ~0.01 ind. m⁻³ and reached 0.35ind. m⁻³ in November 2012 before disappearing (Delpy et al., 2016). Most likely *B. ovata* was co-introduced with *M. leidyi* and was found when salinity was 26, which is optimal for this species (Shiganova et al., 2004a). However, in the following years *B. ovata* did not occur regularly and was never found in Bages-Sigean (D. Bonnet, obs.) in spite of *M. leidyi* occurrence, probably due to variable salinity.

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*Aurelia aurita* competes with *M. leidyi* for food (Delpy et al., 2012) and occurs in both lagoons in low abundances. However, the population dynamics of both species are different: with *Aurelia aurita* blooming in spring and *M. leidyi* in summer-autumn (D. Bonnet obs.).

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Thus, *M. leidyi* was established in Berre and Bages-Sigean lagoons and created autonomous populations, which are absent in the adjacent coastal areas.

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### 3.2.11. Catalan coast of Spain

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*M. leidyi* was first recorded along the Catalan coast and along the entire coast from Cap de Creus to Alcanar in summer 2009 (Fig. 3; 5D) in large swarms observed from early July to late August. In addition, it was recorded in Denia (Valencia) and in Cabrera (Balearic Islands) areas. It was observed at salinities 34-38.2 and temperatures 22-25°C from May to September in the coastal Catalan waters (Fuentes et al., 2009). The shelf waters were characterized by high spatial variability of environmental conditions due to freshwater inputs from continental runoff (Salat et al., 2002). *M. leidyi* was reported along the coast and was not found
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in estuaries. It created a self-sustaining population in the coastal Catalan waters, where reproduction now
occurs almost year-round. Peak reproduction occurs in winter (December-January) when the temperature is
about 10-12 °C, and continues until May. During summer (July-August), when temperature is between 27-30
°C, no reproduction was observed in 2010 and 2011 (Fig. 5D) but it occurred during the summers of 2012
and 2013 at lower temperatures. Size ranges from 0.4 to 18.0 mm in winter, with a mean of 2.6 mm and
mainly adults 25.0-120.0 mm, mean 58.0 mm in summer. In autumn, there is a wide diversity of size 2.0-
70.0 mm with a mean size of 35.0 mm.

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Among its predators *Beroe spp.* were recorded only in spring and early summer along the Catalan coast. At the beginning of July 2009, both *M. leidyi* and *Pelagia noctiluca* were present in the coastal waters and *P. noctiluca* preyed upon *M. leidyi* (Tilves et al., 2013).

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3.2.12. Mar Menor lagoon, Iberia, Spain

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Mar Menor lagoon is a shallow lagoon with an average depth of 3.5 m and is hypersaline (42-47)
(Velasco et al., 2006). Water temperatures range here is 10-32 °C (Pérez-Ruzafa et al., 2004). The lagoon is
separated from the Mediterranean Sea by La Manga, a 20-km-long and 100-900 m-wide sand-bar, which has
five shallow inlets, including the Estacio Channel (Pagès, 2001).

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In summer 2012, *M. leidyi* was observed in the area 37° 38′-37° 50′ N and 0° 43′-0° 57′ W, located in the SE Iberian Peninsula, with an average abundance of 0. 234 ind. m⁻³ in early August, declining to 0.082 ind. 100 m⁻³ by early September. The population contained only adults (total length 19-79 mm), which increased in size during the summer. The Mar Menor lagoon is anthropogenically-disturbed and may be favorable for this species occurrence. *M. leidyi* was recorded also in 2013, but was absent later. No evidence of reproduction was observed and this location is probably a temporal sink area for *M. leidyi* occurrence (Marambio et al., 2013).

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3.2.13. Portuguese coast

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In April 2017 *M. leidyi* was recorded in three important fish nursery areas along the Portuguese coast – the Ria Formosa lagoon, and the Sado and Guadiana estuaries. The water temperature there ranged in 17.4-19.9 °C and salinity in 34.9-35.3 (Crus et al, 2018). The collected specimens were still in their larval stage and had similar sizes (range: 0.8-6.5 mm; average: 2.6 ± 1.2 mm; t = 1.79, d. f. = 24, p = 0.086). The
maximum average abundance of zooplankton (5743 ± 2326 ind. m⁻³) was recorded on April 11, 2017. The total zooplankton abundance in the Ria Formosa lagoon appears to be high enough to sustain population growth and there was a negative correlation between total abundance of zooplankton and the abundance of *M. leidyi* through the tidal cycle on this sampling date (*r* = 0.61, *p* < 0.05) (Crus et al, 2018).

Although ballast water is an efficient introduction vector, dispersion of propagules by currents from adjacent regions could also be cause of the its introduction in Portuguese coastal waters (Crus et al, 2018).

A scyphozoan, *Catostylus tagi* (Haeckel, 1869) is the only putative predator of *M. leidyi* in Portuguese ecosystems. However, its predation pressure seems to be restricted to summer, and it probably would not be high enough to control *M. leidyi* populations.

### 3.2.14. Lakes of the Fayum, Egypt

In 2013, *M. leidyi* was first recorded in a true lake, Birket Qarun in the Fayum, Egyptian Desert, by fishermen finding substantial jelly accumulations in their nets. Because the original inoculum must have been small, this pushes the likely date of the introduction back to around 2010 or earlier. In 2014, *M. leidyi* greatly expanded in numbers and was also recorded in lake El Rayan II, south of Birket Qarun. In spring 2014, there was a bloom of *M. leidyi* at two survey stations with abundances up to 40 ind. m⁻³ (mean size was 30-40 mm, with few specimens up to 60 mm). Both lakes are saline, with Birket Qarun currently more concentrated than seawater (El Shabrawy and Dumont, 2009).

The Fayum lakes (Birket Qarun and Rayan lakes) are fed by Nile water, first pumped up to irrigate the agricultural areas surrounding them, and then drained to the lake(s) since they are situated in a depression below sea level. As soon as the ancient permanent link with the Nile was severed, salinity in Birket Qarun started rising. Around the beginning of the 20th century, the lake became mesohaline. At present it is hypersaline with salinity 40-45. Most probably *M. leidyi* was brought to the lakes with mullet fries from aquaculture facilities in the Nile Delta. So, *M. leidyi* has now crossed yet another barrier, that between the sea and two true land-locked lakes, Birket Qarun and Lake El Rayan II (El-Shabrawy and Dumont, 2016).

### 3.2.15. Red Sea
M. leidyi was recorded for the first time in the Egyptian waters of the northern Red Sea during
surveys conducted along Hurghada coast (between latitudes 27°14.362' and 27° 8.371' N, and longitudes 33
°51.235' and 33° 51.235' E.), conducted from August 2014 to July 2015. In spite of long-term surveys M.
leidyi was recorded only in May (Zaghloul et al., in press).

**3.3. Chronology of M. leidyi invasion in the Northern recipient seas and adjacent areas**

**3.3.1. The North Sea**

The North Sea is a relatively shallow basin, dynamically governed by large-scale cyclonic gyre.
Salinity range is 32-35. In the open sea and in the west, seasonal changes of surface salinity are insignificant
(Brown et al., 1999). The temperature ranges within -1 - + 5 °C in winter and 15-21 ⁰C in summer (Table 1).

*M. leidyi* was discovered first in 2005 in several locations far from each other (Fig 3; 7): in Skagerrak in Oslo (Norway) and Tjarno (Sweden) Fjords (Oliveira, 2007; Hansson, 2006) and along the coasts of the Eastern English Channel and the North Sea: Western and Eastern Bay of Seine and French coasts of the North Sea (Antajan et al., 2014) (Figs. 7, 8A), which suggest independent simultaneous introductions with ship ballast waters.

In 2006 *M. leidyi* was discovered in Skagerrak Gullmar Fjord (Sweden) (Vergara-Soto et al., 2010) and in Kattegat in Helsinger (Tendal et al., 2007) and Horsens Fjords (Denmark) (Jaspers et al., 2017). In addition in 2006 *M. leidyi* was recorded further north in Bergen (Norway) (Hansson 2006), and to the south in several locations in Nissum Fjord (Denmark) (Tendal et al., 2007).

Further to the south *M. leidyi* was reported in Helgoland (Germany) in 2006 (Boersma et al. 2007), in
Dutch coastal waters (Faasse and Bayha 2006, Van Walraven et al., 2013), and in the two different estuaries,
in the Wadden Sea and in the northern and the southwestern estuaries (the Grevelingen, Oosterschelde and
Westerschelde), often in extremely large aggregations. With the high shipping traffic in Dutch ports, ballast
water transport may be an important vector for *M. leidyi*, resulting in its further invasions elsewhere (Van
Ginderdeuren et al., 2012). In addition, to the south in 2006 *M. leidyi* was recorded in Belgian coastal waters
(Dumoulin, 2007) and in 2007 in Zeebrugge (Belgium) (van Ginderdeuren et al., 2012).

These results suggest that there were multiple and simultaneous introductions in the main harbors,
presumably by large ships arriving in the major European ports of Calais, Dunkirk and Le Havre (France),
Rotterdam (Netherlands), Antwerp, Zeebrugge (Belgium) and Hamburg (Germany) from the northern USA coastal waters (e.g., Narragansett Bay) (Antajan et al., 2014). It acted as the primary vector of the North Sea *M. leidyi* populations introduction (Reusch et al., 2010; Bolte et al., 2013). Local shipping promoted regional distribution as it was observed along the Belgium and Dutch coasts (Faasse and Bahya, 2006; Van Ginderdeuren et al., 2012). Current advection serves as a vector responsible for secondary *M. leidyi* spreading (Fig. 7) (Lehmann and Javidpour, 2010; Schaber et al., 2011; Van Ginderdeuren et al., 2012).

In following years, observations were irregular; however, swarms of *M. leidyi* were reported in fjords of Bergen and Flødevigen between 2013 and 2016, at salinity 28.91 and temperature 13 °C, and in Fanafjorden and Outer Sotra in early October of those years (Figs. 7, 8B). Presence of several size classes and small individuals points at local reproduction (Ringvold et al., 2015). In other regions of Norway, *M. leidyi* was recorded in Oslofjord (September-October 2010), along the southern Norwegian coast and northward from Bergen up to Trondheimsfjord (2009-2012) (Fig. 7) (Hosia et al., 2013). Our analysis of *M.leidyi* distribution and current patterns allow assuming that Swedish coast population could be a source for *M.leidyi* dispersal along the Norwegian western coast.

<figure><img src="image_15.png" /><figcaption>Fig. 7. Distribution of *M. leidyi* (red circles) and currents pattern (arrows) in the North Sea. Years indicate first record.</figcaption></figure>

In the western Dutch Wadden Sea, located further south, *M. leidyi* was recorded in a very high abundance also in 2009 and this location becomes an important source area, seeding the whole Dutch coastal zone. In the Wadden Sea temperature ranges from 1.7 °C in February to maximum of 18–21 °C in May–August, with a decrease to 4.1 °C in December. Salinity significantly varies both seasonally from 30 in January to 15 in April and with tidal phases. Salinity is generally higher during flood than during ebb tide,
except in late summer/autumn. *M. leidyi* is present during the whole year with multiple peaks. Its spawning started in May and reached a peak in mid-June (highest mean 360 ind. m⁻³). A second peak occurred in mid-August (mean density 342 ind. m⁻³ with the highest abundance of 912 ind. m⁻³ in a haul). At peaks the population almost entirely consists of small (<20 mm) individuals (Van Walraven et al., 2013).

<figure><img src="image_16.png" /><figcaption>Fig.8. Interannual and seasonal variability of *M. leidyi* abundance in the North and Baltic seas: A - French coast (Bastian et al., 2014), B - Norwegian Coast (Ringvold et al., 2015), C - Limfjorden (Riisgård and Goldstein, 2014), D - Kiel Bight (data Javidpour). White cells – no data.</figcaption></figure>

The temperature tolerance of *M. leidyi* in the North Sea is considerable, with individuals surviving the cold winters with temperatures below 2 °C at south-eastern coasts. Habitat modeling suggests its source population along the northern Dutch coast and in the German Bight (Lepparanta & Myrberg, 2009). In addition, our comparative analyses of first records with subsequent observations and their chronology in the North Sea allow us to assume that *M. leidyi* established local populations in fjords and bays of Skagerrak and western coast of Norway.

Predators in the region are *Beroe sp.* (preliminary *B. norvegica*) and *Beroe gracilis* (Greve, 1975), and *Chrysaora hysoscella*, which co-occurred with *M. leidyi* in the coastal areas, with inter-annual variation between 2011 and 2012 in summer, autumn and winter (spring was not sampled in 2012 in Dutch waters (Vansteenbrugge et al., 2015). Predation by *Beroe gracilis* was observed but had minor impact on *M. leidyi*. Predatory impact of *M. leidyi* on fish larvae in the Wadden Sea was restricted, but due to its high abundance, impact on zooplankton is hypothesized to be considerable (Van Walraven et al., 2013). In Norwegian coastal waters *B. gracilis* (Ringvold et al., 2015) and *Beroe sp.* (preliminary *norvegica*) were also observed over the
same timescale. In experiments in the North Sea water, *B. gracilis* consumed small-sized *M. leidyi*, while larger individuals were partly bitten (Hosia et al., 2011).

### 3.3.2. The Baltic Sea

The Baltic Sea including Kattegat (Fig. 9) is one of the world's largest brackish basins. Its surface salinity varies from 20-22 in the southwestern part to 1-2 in the northernmost Bothnian Bay and the easternmost Gulf of Finland (Fig. 9) (Lepparanta and Myrberg, 2009). Differences in temperatures and salinities and their seasonal variability determine the occurrence or absence of *M. leidyi*, its source and sink areas (Fig. 9). High populations of the southern North Sea is considered as a source of *M. leidyi* reported in the Baltic Sea and some areas of the Kattegat and Skagerrak following the pattern of the currents in the regions (Fig. 7). *M. leidyi* penetrated into the highly productive (Table 1) and saline (Fig. 9) southwestern part of the Baltic Sea, which is under strong influence of the North Sea currents (Fig. 7). It was first recorded in August 2005 in Danish fjords Felsted Kog and Nissum Fjord (Tendal et al., 2007). In early summer 2006 numerous *M. leidyi* was found off Helsinger Harbor. In October 2006 the species appeared in Limfjorden (Fig. 8C), Isefjord (northern Zeeland) and the northern part of Great Belt. Subsequently, numerous reports of *M. leidyi* were received in the northern Little Belt and Kerteminde Bay in February-March 2007 where the abundance of small 3-5 mm *M. leidyi* reached a maximum of 590 ind. m⁻³ In November 2008 (Riisgård, 2017).

In April-June 2007, the abundance of *M. leidyi* was still low in the Great Belt, but reports indicated wide distribution of *M. leidyi* in all inner Danish waters in July-September 2007, in areas like Limfjorden (Tendal et al., 2007). Limfjorden is one of the major Danish water systems and connects the North Sea via Thyborøn Chanal in the west and to the Kattegat in the east. It is heavily eutrophicated and locally suffers from oxygen depletion in summer. Bottom-dwelling fish have disappeared, while jellyfish and ctenophores, including *Aurelia aurita* and *M. leidyi*, increased. Inflowing water in Limfjorden usually originated from the Jutland Coastal Current that flows northwards along the Danish western coast, carrying mixed water masses from the English Channel and the southern North Sea (Riisgård and Goldstein, 2014).
In Limfjorden *M. leidyi* reached extremely high abundance with maximum in August-September. High abundances up to >800 ind. m⁻³ were observed in the innermost part, showing relatively small individuals of 5 to 15 mm. In the central parts of Limfjorden the biomasses reached 300 ml m⁻³.

Summarizing the pattern of *M. leidyi* distribution in Danish fjords, Riisgård (2017) hypothesized that with the northward coastal currents along the Dutch and Danish west coasts, *M. leidyi* re-invades Limfjorden and possibly other Danish and adjacent waters from the warmer southwestern North Sea every summer, which in cold winters, serve as a source and refugia for *M. leidyi*. Limfjorden in turn is most probably a source with the potential to seed the Kattegat and adjacent Danish waters being a sink area (Fig. 7).

<figure><img src="image_17.png" /><figcaption>Fig. 9. Distribution of *M. leidyi* (blue dots) and salinity conditions in the Baltic Sea (after Tendal et al., 2007; Riisgård, 2017; Javidpour et al., 2006; Schaber et al., 2011; Jaspers et al., 2013; Haraldsson et al., 2013).</figcaption></figure>

In July 2006 *M. leidyi* was recorded in Kiel Bight, when surface water temperature reached 22.6 °C, which was 1.7 °C higher than in July 2005 and 5 °C higher than in October and November respectively. The salinity ranged from 13.1 to 22.2 (Fig.9). *M. leidyi* abundance was 29.5 ±12.7 ind. m⁻³ in October, increasing to 92.3±22.4 ind. m⁻³ in November (Fig 8D). More than 80 % of individuals were ≤5 mm in total length, indicating reproduction (Javidpour et al., 2006). From August 2007 observations indicated successful establishment of *M. leidyi* in Kiel Bight, when a 5-fold higher abundance (505 ind. m⁻³) was observed compared to 2006. In the most sampling areas about 85-90% of the population consisted of small larvae and juveniles of 10 mm lenghs. During winter and spring, abundance dropped, and populations had a high
proportion of adults, which concentrated near the bottom for overwintering. In spring, after temperature rising and the development of the vertical water stratification, the whole population is migrating upward (Javidpour et al., 2009a). Thus, *M. leidyi* established permanent population in Kiel Bight, where its annual cycle is characterized by a main peak in August-September, when it occurs and reproduces in the upper warm layers. After November and through winter no reproduction occurs and the population decreased with temperature drops. As a response to low temperatures, a reduced new generation moves down to deep layers, where it takes refuge (Esser et al., 2004; Costello et al., 2006; Javidpour et al., 2009a).

However, from 2011 to spring 2014 *M. leidyi* was almost entirely absent in Kiel Bight, most probably due to cold winters in those years. Only few specimens were recorded sporadically. Since autumn 2014 *M. leidyi* has occurred again in Kiel Bight with a population outbreak in late summer. The similar pattern was observed in 2015-2016 with maximum density of over 200 ind. m⁻³ recorded in September 2015 (Javidpour data).

From the southwestern Baltic along the northern coast of Germany *M. leidyi* spread to the central Baltic Sea (the Bornholm and north Arkona Basin) in subsequent years (Huwer et al., 2008; Javidpour et al., 2006; Kube et al., 2007; Schaber et al., 2011). Observations indicated that there is no self-sustaining population of *M. leidyi* in the central Baltic Sea due to low salinity (Fig. 9). *M. leidyi* most likely re-introduces into the Bornholm Basin every year via lateral advection from the southwestern Baltic. It may live seasonally and reproduces in this area where salinity >7. These findings are important for further assessment of the impact of *M. leidyi* on the pelagic ecosystem of the central Baltic (Schaber et al., 2011; Jaspers et al., 2013). Investigations of the seasonal changes in abundance and distribution of *M. leidyi* in the central Baltic Sea from April 2007 to May 2010 (Schaber et al., 2011) indicated highest abundances in spring and autumn, and absence or only sporadic appearance of *M. leidyi* during summer. The vertical distribution of *M. leidyi* was mostly confined to water layers below the permanent halocline. Schaber et al. (2011) assumed that food limitation plays a major role in the decline of *M. leidyi* in the central Baltic during summer. Observation in northwestern Baltic proper, Bothnian basin showed absence of *M. leidyi* in the areas with salinity <7 (Haraldsson et al., 2013). So, in the low saline (7-8) Central Baltic *M. leidyi* was sporadically observed with
low abundance (mean 0.02 ind. m³ - 1.16 ind. m³) (Fig. 9). Probably, low salinity restricts reproduction and establishment of *M. leidyi* there (Jaspers et al., 2011).

Bolte et al. (2013) studied *M. leidyi* in the North and Baltic Seas by analyzing genetic changes over 3 years (2008-2010) and found limited gene flow between the North Sea and the southwestern Baltic Sea, and successful reproduction in both areas. In the eastern part of central Baltic Sea (Bornholm Basin), the genetic diversity decreased during the study, indicating that this area is a sink for *M. leidyi*.

Dispersal models suggested that *M. leidyi* undergoes wind driven dispersal in the brackish surface layer east- and northward from the Bornholm Basin, where *M. leidyi* has been observed since 2007. However, in the northern Baltic survival is possible only in its southernmost part, like Pomeranian and Gdansk Bays (Janas et al., 2007; Jaspers et al., 2018). *M. leidyi* is absent in the Gulf of Bothnian, Finland and Riga Bays and along Estonia, Latvia, Lithuania and Russian coast due to low salinity (3-6.5) (Fig. 9). Nevertheless, the observations of penetration and minor reproduction of *M. leidyi* in the waters with salinity 6, observed in the Northern Caspian and Azov seas, in Narragansett Bay and Chesapeake Bay (Costello et al., 2012; Purcell et al., 2001; Shiganova et al., 2004 b), should be taken into consideration if the temperature continues to rise in the Baltic Sea (Fig. 2).

Thus, the environmental conditions for *M. leidyi* reproduction are most favorable in the southwestern Baltic. It reaches high abundances in the disturbed and often euthrophicated Kiel Bight and Danish bays and fjords and adjacent waters.

Among predators should be mentioned *Cyanea capilatta*, which occurs in Kiel Bight; it is preyed on *M. leidyi* in feeding experiments by Hosia et al. (2011) but 90% of encounters ended in escape. In addition, seasonal overlapping of these two species in the Kiel Bight is limited by the early autumn when *M. leidyi* population is already diminished. Among predators in February 2016 in Kiel Bight *Beroe sp.* was recorded sporadically, but species-level identification was impossible (Javidpour, persobs).

In Danish fjords three species *Beroe: Beroe cucumis*, *B. gracilis* and *B. ovata* were observed, with the latter two species observed for the first time in the Baltic Sea (Shiganova et al., 2014b). *Beroe spp.* probably arrive from the North Sea, but at irregular intervals and therefore their effect on the *M. leidyi* population size was not clearly seen (Riisgård, 2017).
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## 4.1 Summary of *M. leidyi* distribution patterns and seasonal dynamics in recipient and native areas

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We have summarized current harmful invader *M. leidyi* expansion around the Eurasian seas and patterns of its establishment and distribution. The Black Sea has been the first recipient and then donor area of *M. leidyi* introduction in the most of the Southern seas (Ghabooli et al., 2011, 2013). Supposedly in late 1980s, *M. leidyi* has expanded from the Black Sea, with the currents eastward in the Sea of Azov, which became a sink area, and with ballast waters was brought in the Caspian Sea and south-westward to the Sea of Marmara and the eastern Mediterranean Sea. Antropogenic and climatic changes of environmental conditions made these locations physiologically favorable for *M. leidyi*. Since 2009 *M. leidyi* has become widespreaded further throughout the Western Mediterranean and established, mainly in disturbed coastal areas, bays, estuarias, and lagoons, which became sources for its continued expansion as far as estuaries of southern Portugal (Cruz et al., in press). So, both local currents and shipping were the probable vectors for *M. leidyi* transportation around the Mediterranean and other Southern Eurasian seas. However, it should be taken into consideration that current advection covers a relatively short distance (e.g., particle travel for 300 km takes 350 days, with the typical mean current velocity 1 cm/s), which is much longer than the duration of *M. leidyi* annual reproductive age. That may explain why it took long time (from 1990 to 2009) for *M. leidyi* to spread throughout the Mediterranean Sea. Moreover, this is an overestimation since the eddy dynamics patterns of the flow may slow down the current transportation. One more requirement for *M. leidyi* during dispersal is to find somewhere on the way suitable conditions for reproduction and creation of a self-sustaining population. Otherwise dispersed populations vanish with the advent of unfavorable conditions such as a strong decrease or increase of temperature or extreme salinity or oligotrophic conditions with lack of enough food. So, the currents can be only of local importance. The primary vector of the multiple introductions is the ship ballast waters.

In the Northern region *M. leidyi* was first introduced in the North Sea (Reusch *et al.*, 2010) where it has been recorded in several locations since 2005. One of the main source areas, where it reaches very high abundance became southeastern coastal areas and estuaries along the northern Dutch coast and in the German Bight influenced by riverine inflow, where the environment allows overwintering (Lepparanta &
Myrberg, 2017). In addition, comparison of first records and subsequent observations in the North Sea provide us understanding that *M. leidyi* established local source populations in fjords and bays of Skagerrak and western coast of Norway as well.

From the Dutch areas with the northward coastal currents (Fig. 7) during spring warming *M. leidyi* spreads every year in the Baltic Sea, in Danish fjords and adjacent waters (Riisgård, 2017). In the Kiel Bight *M. leidyi* created permanent population originated from the North Sea with possible elimination during cold winters (as it happened in 2011-2014) and re-invaded from the North Sea again (Jaspers et al., 2018).

Recently Jaspers et al. (2018) hypothesized that *M. leidyi* could be transported by currents from the English Channel, the Southern North Sea and Norway towards north-west Denmark, continuing with an anticlockwise gyre through the Skagerrak and then northwards along the western Norwegian coast as far north as 64° N. However, the quoted rates of that re-colonization of up to 2000 km per season seem to be doubtful. For instance, to transport a particle over 2000 km during one season the mean current velocity should be 25 cm/s, which is unrealistic.

Our assessment has confirmed that invasion success is determined by the complex interaction of global shipping and local population dynamics as earlier described by Seebens et al. (2019).

We intently investigated seasonal and interannual variability of permanent and temporal occurrence of *M. leidyi* throughout the Eurasian recipient seas with sources, sinks and refugia areas. We have figured out temporal characteristics of development and reproduction of *M. leidyi* population during the year in studied areas based on authors’ long-term data. We found that *M. leidyi* with its high physiological tolerance and capacity for adaptation demonstrated different patterns of spatial distribution and seasonal dynamics depending on environmental conditions. *M. leidyi* has adapted to local conditions, changing its phenology to maximize duration of seasonal development and areas of distribution in different Eurasian seas, including sources and sinks. In addition, we found out that physiological limitations and environmental restrictions of *M. leidyi* reproduction and its duration is different in Eurasian seas. The seasonal start and duration of reproduction depend on temperature, salinity and food availability, i.e. concentrations of microzooplankton for larvae and mesozooplankton for juveniles and adults.
<table><caption>Table 3. Periods of *M. leidyi* reproduction (grey stripes) and peaks of abundance and reproduction (black stripes) and corresponding favorable environmental conditions: temperature (T), temperature of reproduction (T, R) salinity (S), peak of zooplankton (Z) in the recipient habitats</caption><thead><tr><th>AREA/MONTH</th><th>J</th><th>F</th><th>M</th><th>A</th><th>M</th><th>J</th><th>J</th><th>A</th><th>S</th><th>O</th><th>N</th><th>D</th><th>T°C</th><th>T°C, R</th><th>S</th><th>Z</th><th>References</th></tr></thead><tbody><tr><td>Black Sea (&lt;2006)</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>5-25</td><td>21-25</td><td>12-22</td><td>+</td><td>Shiganova et al., 2004</td></tr><tr><td>Black Sea (&gt;2006)</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>8-30</td><td>18-26</td><td>12-22</td><td>+</td><td>Shiganova et al., 2018</td></tr><tr><td>Sea of Azov</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>-0.8-30</td><td>18-26</td><td>6-14</td><td>+</td><td>Mirzoyan et al., 2006</td></tr><tr><td>Southern Caspian</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>10-30</td><td>10-30,5</td><td>12.6-13</td><td>+</td><td>Shiganova, 2011</td></tr><tr><td>Middle Caspian</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>5.8-26</td><td>18-26</td><td>12.1-12.6</td><td>+</td><td>Shiganova, 2011</td></tr><tr><td>Northern Caspian</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>3.8-28</td><td>23-27</td><td>6.1-10.0</td><td>+</td><td>Shiganova, 2011</td></tr><tr><td>Sea of Marmara</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>8-29</td><td>21-26</td><td>22-29</td><td>+</td><td>Isinibilir, 2012; Shiganova, 1993</td></tr><tr><td>Northern Aegean</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>ND</td><td>ND</td><td>ND</td><td>12-27</td><td>21-25</td><td>33-39</td><td>+</td><td>Siapatis, 2014</td></tr><tr><td>Southern Aegean</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>14.5-29</td><td>18-26.5</td><td>37.3-39.6</td><td>+</td><td>Gulsahin, 2013</td></tr><tr><td>Levantine Sea</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>ND</td><td>ND</td><td>ND</td><td>ND</td><td>ND</td><td>17.5-31</td><td>19.5-23.5</td><td>39.3-40.0</td><td>ND</td><td>Galil pers.com.</td></tr><tr><td>Northern Adriatic</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>6-29</td><td>17-28</td><td>11-38</td><td></td><td>Malej et al., 2017</td></tr><tr><td>Legurian Sea</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1-27</td><td>17-21.9</td><td>37.9-38.2</td><td>+</td><td>Lilley, Lombard pers.com.</td></tr><tr><td>Catalan Coast</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>10-30</td><td>10-25</td><td>34-38</td><td>ND</td><td>Marambio pers.com.</td></tr><tr><td>Berre Lagoon</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>3,4-28.2</td><td>10-25.2</td><td>15.9-26.2</td><td>+</td><td>Delpy et al., 2016</td></tr><tr><td>Bages-Sigean</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>9,6-27,1</td><td>18-27</td><td>18.9-34.3</td><td>+</td><td>Delpy et al., 2016</td></tr><tr><td>Portugal coast</td><td></td><td></td><td></td><td></td><td></td><td></td><td>ND</td><td>ND</td><td>ND</td><td>ND</td><td>ND</td><td>ND</td><td>17.2-22.2</td><td>17.4-20</td><td>34.9-35.3</td><td>+</td><td>Crus et al, 2018</td></tr><tr><td>Kiel Bight</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>3.5-22.2</td><td>13.1-22.2</td><td>14-20</td><td>+</td><td>Javidpour et al., 2009a</td></tr><tr><td>Danish Fjords</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>-0.5-24</td><td>12-24</td><td>19-34</td><td>+</td><td>Riisgård, et al., 2015-17</td></tr><tr><td>Central Baltic</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>2-20</td><td>8.4-10.7(>)</td><td>7.8±0.3</td><td>+</td><td>Jaspers et al. 2011, 2013</td></tr><tr><td>Kattegat</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>0-21</td><td>11.±7-21</td><td>25±3</td><td>-</td><td>Jaspers et al. 2011; Haraldsson et al., 2013</td></tr><tr><td>Skagerrak</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>6-20</td><td>>9-20</td><td>25-29</td><td>-</td><td>Haraldsson et al., 2013</td></tr><tr><td>Wadden Sea</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1.7-22</td><td>18-21</td><td>34-35</td><td>ND</td><td>Van Walraven et al., 2013</td></tr></tbody></table>

ND - no data

In temperate Southern seas (Black, Azov, most of Caspian and Marmara) reproduction reaches its peak in summer-early autumn depending on temperature and zooplankton concentration (Table 3). During last decade, reproduction tends to start earlier in May-June due to an earlier increase of spring and summer temperature (Fig. 2) and earlier development of warm water zooplankton species (Shiganova et al., 2014a; 2018).

In the subtropical conditions of the oligotrophic Mediterranean regions with hot summers, *M. leidyi* increases seasonal abundance and reproduces in spring and autumn and sometimes in winter, which coincides with seasonal zooplankton development in these areas (Aegean Sea, Levantine Sea, Ligurian coast of France and Italy) (Fig. 5A, B and C; Table 3). In hot summer *M. leidyi* disappears from water column and a reduced new generation occupies deep refugia (Shiganova et al., 2004c; Lombard et al., obs.). In productive northern Adriatic Sea *M. leidyi* reaches high abundances and high reproduction rate in late summer and autumn (Malej et al., 2017). Open parts of the Mediterranean Sea became sinks where *M. leidyi* may spread with the local currents. Part of this dispersal is propagules potentially seeding populations in the
coastal zones, lagoons estuaries and bays. Another part is a sterile dispersal, where *M. leidyi* may survive
temporally without reproduction.

In the Northern European seas seasonal dynamics are similar to those in temperate Southern seas (Table 3) but reproduction time and duration has not been studied in details. Probably, reproduction duration is shorter and the peak has to be in the warmest months in most of cases coinciding with peak of zooplankton abundance. In specific conditions of the Wadden Sea with flood and ebb tides reproduction was observed during two periods (May-June and mid-August) and remained high until October (Van Walraven et al. 2013) (Table 3).

Meanwhile, modeling assessment for the North Sea (Collingridge et al., 2014) indicated that reproduction might be possible for most of the year according to estimated environmental conditions (up to 212 days in 2011), but this is highly improbable in the Northern sites.

In the Baltic Sea *M. leidyi* reproduces most intensively in the productive Kiel Bight and Danish Fjords with a peak of abundance in late summer-early autumn (Fig. 8C, D; Table 3) with highest concentration in Limfjorden (Javidpour et al., 2006; 2009a; Riisgård and Goldstein, 2014). In Limfjorden *M. leidyi* probably re-invades from the North Sea every year as into sink area of south-eastern coastal populations of the North Sea. On the other hand, Limfjorden is probably a source area for other Danish fjords and adjacent waters (Riisgård, 2017). *M. leidyi* reproduction was observed also in the central Baltic Sea, but it was indicated that it is a sink area of southwest Baltic where *M. leidyi* may live seasonally and reproduce if salinity >7 (Schaber et al., 2011; Haraldsson et al., 2013).

Thus, in the disturbed areas of the North Sea (Dutch coastal waters including Wadden Sea) and the Baltic Sea (Kiel Bight, Limfjorden) *M. leidyi* could reach much higher abundances than in the most of the southern seas and amounts to abundance comparable with the Sea of Azov and the Caspian Sea (Figs. 4, 8).

Our general assessment suggests multiple and sometimes simultaneous *M. leidyi* introductions in the main harbors of Southern (Mediterranean areas) and Northern seas, presumably by large ships, and its subsequent local dispersal throughout the connected seas and water bodies.

The transfer of *M. leidyi* with aquacultures activities indicates a new vector of introduction to the hypersaline Fayum lakes of Egypt.
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To summarize, we conclude that *M. leidyi* found suitable temperature, salinity and productivity conditions to create populations in the Black, Caspian and Azov Seas, including source and sink areas, in the coastal areas, bays and lagoons of the Mediterranean and in the coastal waters, fjords and estuaries of the Baltic and North seas. In the seas where it cannot persist during the full annual cycle, *M. leidyi* could find sink areas or suitable refugia to survive through the most unfavorable conditions (very low temperatures as sometimes in the Black, Baltic and North seas or very high temperature as in Southern Aegean, Levantine, Ligurian seas) and recover populations with improving conditions or re-introductions in the case of extinction. We showed the possibility of this species to establish autonomous populations in closed basins (isolated Caspian Sea, Egyptian land-locked lakes), where it may complete its annual cycle. In some regions populations are eliminated during sharp winter cooling in the sink areas (Sea of Azov, Northern and Middle Caspian) and re-builds again every year with arrival of a new generation from the source area (Black Sea; Southern Caspian). *M. leidyi* has been found throughout a wide range of environmental conditions, from temperate to subtropical regions, in brackish and marine and even hyperhaline waters. Environmental conditions shape its patterns of spatial distribution and phenology. There are at least two eco-types in the resident seas of Eurasia. The temperature and salinity thresholds of establishment and life cycle of the southern (the Black, Caspian, Azov, Mediterranean Seas), and the northern (the Baltic and North Seas) reflect conditions in their donor areas (the Gulf of Mexico and Narragansett Bay).

Apart of that, we compared environmental conditions, time and rate of reproduction in the recipient Eurasian seas with the native locations in the Northern America from where they were introduced (Ghabooli et al., 2011; 2013; Reusch et al., 2010, Bayha et al, 2015). Native subtropical estuaries of Biscayene Bay, Florida are indicated as a donor for the Black Sea and consequently to the most of the Southern Eurasian populations (Ghabooli et al., 2013). In those estuaries temperature range is 18-32 °C and salinity ranges from mesohaline <20 to hypersaline >40 depending on season and location. *M. leidyi* does not reproduce in summer in high salinity and high temperatures, its peaks of abundance and reproduction is observed in spring, autumn and early winter (Table 4) (Kremer, 1994; Purcell et al., 2001). Similar environmental conditions and, consequently, seasonal dynamics and time of reproduction are observed in the Mediterranean Sea, where reproduction occurs in spring and autumn and in some areas in early winter
<table><caption>**Table 4.** Periods of *M. leidyi* reproduction (grey stripes) and peaks of abundance and reproduction (black stripes) and corresponding favorable environmental conditions: temperature (T), temperature of reproduction (T, R) salinity (S), peak of zooplankton (Z) in the native habitats</caption><thead><tr><th>AREA/MONTH</th><th>J</th><th>F</th><th>M</th><th>A</th><th>M</th><th>J</th><th>J</th><th>A</th><th>S</th><th>O</th><th>N</th><th>D</th><th>T °C</th><th>T °C-R</th><th>S</th><th>Z</th><th>References</th></tr></thead><tbody><tr><td>Narragansett Bay, RI</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1-25</td><td>10-23</td><td>21-32</td><td>+</td><td>Costello et al., 2012</td></tr><tr><td>Mid Chesapeake Bay, MD</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>2-30</td><td>12-29</td><td>5-16</td><td>+</td><td>Lonsdale, 1981; Olson, 1987; Purcell et al., 2001</td></tr><tr><td>Biscayne Bay, FL</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>18-32</td><td>18-28</td><td>14-45</td><td>+</td><td>Baker, 1973</td></tr><tr><td>Nueces Estuary, TX</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>10-30</td><td>10-30</td><td>20-38</td><td>+</td><td>Buskey, 1993</td></tr><tr><td>Rio de la Plata estuary, ARG</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>7.5-25</td><td>10-25</td><td>9-24</td><td>+</td><td>Mianzan et al., 1996; Sorarrain, 1998</td></tr><tr><td>Blanca bay, ARG</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>5-24</td><td>10-24</td><td>24-38</td><td>+</td><td>Mianzan & Sabatini, 1985; Mianzan, 1986</td></tr><tr><td>Nord Patagonic Tidal front, ARG</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>10-16</td><td>10-16</td><td>33</td><td>+</td><td>Mianzan et al., 1996, 2010; Mianzan pers. obs</td></tr></tbody></table>

In warm coastal waters of the Gulf of Mexico including subtropical waters of both St. Andrey Bay, Florida and the Nueces (Texas) Estuaries, the annual temperature range is 10-30 °C and salinity ranges 20-33. *M. leidyi* is abundant there year-round with peaks in late summer in areas where zooplankton biomass is high (Table 4) (Kremer, 1994). Environmental conditions and seasonal dynamics similar to subtropical waters of Gulf of Mexico are observed in the Southern Caspian (Table 3).

In the colder waters such as Narragansett Bay, near the northern end of the geographical range for *M. leidyi*, annual temperature ranges 1-25 °C with temperature >20 °C from June to September, salinity range 25-32 (Table 4). This area is indicated as a donor for the Northern seas populations (Reusch et al., 2010; Ghabooli et al., 2011). Minor eggs releases at temperatures as low as 6 °C, but 10 °C is a good approximation of a threshold for successful egg production and its rates increase with the temperature rise. Thus, temperature range for reproduction is 10-23 °C with some reproduction at 25 °C (Costello et al., 2012). Recipient Northern European seas have temperature close to that in Narragansett Bay. However salinity values are close to Narragansett Bay only in the North Sea, where *M.leidyi* first established, and which is the main source area for both northern seas. The beginning of reproduction (April, at 14 °C) and the peak occurs earlier (July-August) than in the North and Baltic seas but at the same temperature, when waters become warmer.

In Chesapeake Bay *M. leidyi* reproduction starts from mid-April to early June and it is most intensive between June and September (Table 4) at the temperatures of 12-29 °C and at salinity 6-16 (Kremer, 1994;
952

Purcell et al., 2001). The seasonal pattern and environmental conditions in Black, most of Caspian, and Azov seas are close to Chesapeake Bay, However, reproduction in all three seas are observed in summer. During recent years with temperature is rising in spring and summer *M. leidyi* begin to reproduce in late spring (Fig 4, Table 3).

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Based on the analyses of conditions in recipient and donor areas we identify the following constraints on *M. leidyi* occurrence and reproduction and population growth:

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**Occurrence conditions.** There are areas of occurrence of self-sustainable *M. leidyi* populations with the possibility to reproduce in certain seasons. And there are areas, where it can spread and survive temporary without reproduction in the unfavorable conditions. Acceptable environmental conditions for *M. leidyi* occurrence have been summarized in Fig 10A, C.

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Acceptable water temperatures under which *M. leidyi* occurs are variable and range between >3 and 30°C for southern seas and 1-24°C (maximal temperatures) for northern sea recipient areas (Fig. 10A).

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Acceptable salinity at which *M. leidyi* occurs ranges between 3.5-45 in southern seas and 4.5-35 in northern seas (Fig 10A).

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Surface chlorophyll concentration has been taken as indicator of ecosystem productivity and is similar to using the concentration of microplankton and mesozooplankton. According to field data, *M. leidyi* requires a mean Chl level above 0.1 mg.m⁻³ (Fig 10C).

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<figure><img src="image_18.png" /></figure>
Fig. 10. Ranges of SST, SSS and Chl values, sufficient for *M. leidyi* general occurrence (A, C) and reproduction and population growth (B, D). Compiled from *in situ* data from various recipient basins.

**Reproduction conditions.** Areas with environmental conditions favorable for reproduction and growth of *M. leidyi* self-sustaining population, which includes source and sink areas summarized in Fig 10B and D.

The range of water temperature favorable for *M. leidyi* reproduction and population growth is 12°C<SST<27°C for the Southern seas. Below 11.8 °C, *M. leidyi* stops active reproduction. However, in productive areas of the Southern Caspian and Northern Adriatic reproduction was recorded at higher temperature, such as 29 °C and 28 °C respectively (Fig 10B). In the Northern seas, temperature favorable for reproduction ranges between 10-24 °C (Fig 10B). In the Northern Caspian, in Narragansett Bay and Chesapeake Bay minor reproduction is recorded at 6°C (Costello et al., 2012; Purcell et al., 2001).

Water salinity for *M. leidyi* reproduction and growth of a population is in the range 6-40 (Fig 10B).

Productivity conditions, favorable for *M. leidyi* reproduction starts from Cl³⁻ ≥0.5 mg. m⁻³ (Fig. 10D).

The data array on *M. leidyi* occurrence, reproduction and population growth, compiled in this study, were also used to generate a model that successfully accounts for past and current patterns and uses this capability to predict future invasive patterns (Shiganova et al., 2019).

**4.2. Impact**

*M. leidyi*'s impact on zooplankton was considerable in temperate southern seas (Black, Azov, and in some years in the Sea of Marmara and its bays). In these seas bottom up and top down impact on the most of trophic levels was observed before *B. ovata* arrived (Shiganova et al., 2004 a, b). Now these ecosystems are recovering, but still there is an impact during the summer peak of *M. leidyi*. However, its effect is getting shorter with each year. There is no predator in the Caspian Sea and ecosystem disruption at all trophic levels increases from year to year (Shiganova, 2011). High impacts were found in the Baltic in Kiel Fjord and Limfjorden (Javidpour et al. 2009a; Riisgård and Goldstein, 2014). In the North Sea *M. leidyi* impact on zooplankton seems considerable in regions such as the Dutch coastal areas and the Wadden Sea (Van Walraven et al., 2013). This is the result of much higher abundances than recorded in native regions, where the highest biomass estimated in the Narragansett Bay was up to 100 ml. m⁻³ (Kremer, 1994). Therefore, the dramatic expansion of *Mnemiopsis leidyi* in the seas of Eurasia and in saline lakes is alarming, in
combination with enlargement of euthrophicated areas, a growing aquaculture sector and decreasing fish stocks. The only positive factor is the increasing dispersal of the invasive *B. ovata*, which follows *M. leidyi* to new areas and the active migration of native *Beroe spp.* into areas of *M. leidyi* blooms.

### 4. 3. Prey

Food for juveniles and adults of *M. leidyi* includes mesozooplankton, meroplankton, small pelagic fish and fish eggs (Costello et al., 2012).

It is important to stress out that in all brackish seas (north-western Black Sea; Sea of Azov, Caspian and Baltic Seas, parts of the Sea of Marmara and coastal waters of brackish Mediterranean lagoons) the main food is the non-native copepod *Acartia tonsa* and in most of them also larvae of the non-native barnacle *Amphibalanus improvises*. Both species were introduced in the Black, Baltic and Caspian seas and to Berre Lagoon (Gomoiu and Scolka, 1996; Gubanova, 2000, Delpy, 2012) probably from the Atlantic coast of America. From the Black Sea they were introduced into the Sea of Azov and Caspian Sea (Shiganova, 2009). Interestingly, the same fast growing, warm water copepod *A. tonsa* is also a *M. leidyi* prey in coastal waters of America (Kremer, 1994).

Unusual prey consumption was observed seasonally in Kiel Bright. In winter, the diet was mostly composed of slow-moving mesozooplankton like larval *Amphibalanus improvisus* (on average, 82% of total prey found in the gut). In contrast, the relative abundance of crustacean zooplankton in the diet was low: copepods reached 6% and cladocerans 1% of total prey (Javidpour et al, 2009). In August, ctenophore larvae larger than 5 mm were dominant in the gastrovascular cavity of adults and contributed up to 76% of the total while copepods ranked second in prey captured (23%). In late summer, *M. leidyi* fed mostly on planulae of *Aurelia aurita* (57% in September and 72% in October), while the relative share of copepods was only 14%. Predation of *M. leidyi* on planulae of *Aurelia aurita* and on own larvae, which were observed in the Kiel Bright (Javidpour et al, 2009), has not been observed in other habitats to date.

### 4.4. Predators and competitors

Our results show that in the most temperate seas, coastal waters, lagoons, fijords and estuaries *Aurelia aurita* is the main native competitor of *M. leidyi* (Table 5), which abundance was suppressed by *M. leidyi* as more successful competitor in most of areas. However, in the northern Adriatic periods of
occurrence of *A. aurita* and *M. leidyi* do not overlap: *A. aurita* is most abundant from March to June, while *M. leidyi* (since 2016) appears later in summer and is most abundant in autumn. In contrast, occurrence of *Cotylorhiza tuberculata* overlaps with *M. leidyi* as well as *Rhizostoma pulmo* (which also have a peak of abundance of largest individuals in late autumn).

In Southern semi-enclosed seas with *M. leidyi* populations, its predator *Beroe ovata* sensu Mayer follows it shortly and these ecosystems are gradually recovering (Black Sea, the Sea of Marmara, and Azov). Invading *B. ovata*, native *B. cucumis* sensu Mayer and *B. forskalii* control the populations of *M. leidyi* in the Levantine Sea. Their presence completely stopped the establishment of *M. leidyi* in the northern Adriatic in 2005 (Shiganova and Malej, 2009).

<table><caption>Table 5. Native and non-native gelatinous species in studied areas</caption><thead><tr><th>Location</th><th>Native gelatinous competitors</th><th>Invasive gelatinous competitors</th><th>Native predators availability</th><th>Invasive predators availability</th><th>Reference</th></tr></thead><tbody><tr><td>Black Sea</td><td>Aurelia aurita (L.)<br/>Rhizostoma pulmo (Macri)<br/>Pleurobrachia pileus (Müller)</td><td>No</td><td>No</td><td>Beroe ovata</td><td>Shiganova, 2009</td></tr><tr><td>Sea of Azov</td><td>No</td><td>No</td><td>No</td><td>Beroe ovata</td><td>Mirzoyan et al., 2006</td></tr><tr><td>Caspian Sea</td><td>No</td><td>Aurelia aurita</td><td>No</td><td>No</td><td>Ivanov et al., 2000</td></tr><tr><td>Sea of Marmara</td><td>Aurelia aurita<br/>Rhizostoma pulmo</td><td>No</td><td>No</td><td>Beroe ovata</td><td>Isinibilir et al., 2015</td></tr><tr><td>N. Aegean Sea coastal waters</td><td>Aurelia aurita</td><td>No</td><td>Temporary<br/>Beroe forskalii,<br/>B. sensu cucumis</td><td>Beroe ovata</td><td>Shiganova et al., 2004</td></tr><tr><td>S. Aegean Sea Gokava Bay</td><td>Aurelia aurita<br/>Cotylorhiza<br/>tuberculata<br/>Cestum veneris</td><td>No</td><td>Beroe mitrata</td><td>No</td><td>Gülşahin and Tarkan, 2014</td></tr><tr><td>Levant Basin Israel coast</td><td>No</td><td>Rhopilema<br/>nomadica Galil, 1990</td><td>Temporary<br/>Beroe forskalii,<br/>B. sensu cucumis<br/>Beroe mitrata</td><td>Beroe ovata</td><td>Galil et al., 2009, 2011</td></tr><tr><td>N. Adriatic Sea</td><td>Temporary<br/>Aurelia aurita<br/>Bolinopsis vitrea (L. Agassiz),<br/>Leucothea multicornis (Quoy&Gaimard)</td><td>No</td><td>Temporary<br/>Beroe forskalii,<br/>B. sensu cucumis<br/>Pelagia<br/>noctiluca</td><td>Temporary<br/>Beroe ovata</td><td>Shiganova and Malej, 2009</td></tr><tr><td>NW Mediterranean S. Catalan Coast</td><td>No data</td><td>No</td><td>Pelagia<br/>noctiluca<br/>Beroe spp</td><td>No</td><td>Tilves et al., 2013</td></tr><tr><td>Berre Lagoon</td><td>Aurelia aurita</td><td>No</td><td>No</td><td>Temporary<br/>Beroe ovata</td><td>Delpy et al., 2012</td></tr><tr><td>Bages-Sigean</td><td>Aurelia aurita</td><td>No</td><td>No</td><td>No</td><td>Delpy et al., 2016</td></tr></tbody></table>
<table><thead><tr><th>lagoon</th><th></th><th>Journal Pre-proof</th><th></th><th></th></tr></thead><tbody><tr><td>Ligurian Sea</td><td>Bolinopsis vitrea (L. Agassiz, 1860), Leucothea multicornis (Quoy&Gaimard)</td><td>No</td><td>Pelagia noctiluca B. sensu cucumis Mayer</td><td>No</td><td>Lilley M. Lombard F. pers.comm.</td></tr><tr><td>W. Baltic Sea Kiel Fjord</td><td>Aurelia aurita</td><td>No</td><td>No</td><td>Temporary Beroe sp.</td><td>Javidpour et al., 2009</td></tr><tr><td>Baltic Sea Great Belt Limfjorden</td><td>Aurelia aurita</td><td>No</td><td>Beroe gracilis B. cucumis</td><td>B. ovata</td><td>Riisgård, 2017</td></tr><tr><td>North Sea</td><td>Aurelia aurita</td><td>No</td><td>Beroe gracilis B. cucumis Chrysaora hysoscella</td><td>No</td><td>Van Walraven et al., 2013</td></tr></tbody></table>

B. ovata was recorded in the Limfjorden simultaneously with native Beroe cucumis (redefined preliminary as B.norvegica) and Beroe gracilis, which arrived from the North Sea to prey on M. leidyi. All of them control M. leidyi abundance temporally (Shiganova et al., 2014b; Riisgård and Goldstein, 2014). In the North Sea in Norwegian coastal waters B. gracilis and Beroe sp. (redefined preliminary as B.norvegica) were first recorded in swarms of M. leidyi (Ringvold et al., 2015; Hosia and Falkenhaug, 2013; Johansson et al., 2018). Generally, B. ovata tends to follow M. leidyi into new areas. However, it may create a self-sustaining population and predator-prey cycles with M. leidyi where both have a permanent occurrence. Native Beroe species both in the Mediterranean and the North seas migrate into M. leidyi blooms and feed on it. In recipient areas, Beroe ovata plays a more significant role than in native Florida and Narragansett Bay, where B. ovata does not occur regularly (Shiganova et al., 2014b). In the southern Aegean Sea (Gökova Bay) M. leidyi is controled regularly by native B. mitrata (identification by Shiganova).

Among other predators, Pelagia noctiluca has the potential to limit M. leidyi population growth in coastal waters of the Mediterranean (Tilves et al., 2013). In the Baltic and North Seas Cyanea capillata may be an important predator (Hosia et al., 2011).

## Acknowledgements

T.A. Shiganova performed this study within the framework of State assignment of the Ministry of Education and Science of the Russian Federation - theme #0149-2019-0010. A.S. Kazmin performed assessment of current advection, contributing to species dispersal within the framework of State assignment of the Ministry of Education and Science of the Russian Federation - theme #0149-2019-0004. Authors also are grateful to Dr. A. Mikaelyan for help with some figures drawing.

## References:

Anninsky BE, Finenko GA, Abolmasova GI, Hubareva ES, Svetlichny LS, Bat L, et al., 2005. Effect of starvation on the biochemical compositions and respiration rates of ctenophores Mnemiopsis leidyi and Beroe ovata in the Black Sea. J. Mar. Biolog. Assoc. U.K. 2005;85: 549-561.
063

064

065

066

067

068

069

070

071

072

073

074

075

076

077

078

079

080

081

082

083

084

085

086

087

088

089

090

091

092

093

094

095

096

097

098

099

100

101

102

103

104

105

106

107

108

109

110

111

112

113

Antajan E, Bastian T, Raud T, Brylinski JM, Hoffman S, Breton G., 2014. The invasive ctenophore *Mnemiopsis leidyi* A. Agassiz, 1865 along the English Channel and the North Sea French coasts: another introduction pathway in northern European waters? Aquat Invasions. 2014;9: 167-173.

Baker LD., 1973. The ecology of the Ctenophore *Mnemiopsis mccradyi* Mayer in Biscayne Bay. Florida. M.Sc. Thesis. The University of Miami, Miami, Florida, USA. 1973.131 pp.

Bagheri S, Mansor M, Turkoglu M, Makaremi M, Babaei H., 2012. Temporal distribution of phytoplankton in the southwestern Caspian Sea during 2009-2010: a comparison with previous surveys. J Mar Biol Assoc UK. 2012;92(06): 1243-1255. doi:10.1017/S0025315412000094

Bastian T., Antajan E., Dorothée V. 2014. Looking for Mnemiopsis leidyi in Dunkirk Harbour (Southern North Sea, France). Report of the Joint CIESM/ICES Workshop on *Mnemiopsis* Science (JWMS), 18–20 September 2014, A Coruña, Spain. ICES CM 2014/SSGHIE:14. 80 pp.

Bayha KM, McDonald J, Harbiso GR, Gaffney PM., 2002. The Molecular Systematics of the Invasive Ctenophore Mnemiopsis sp. // The Ctenophore *Mnemiopsis leidyi* in the Black, Caspian and Mediterranean Seas and other aquatic invasions. Editors Dumont H, Shiganova T, Niermann U. NATO ASI Series 2. Environment. Kluwer Academic Publishers. Abstract. 2002.

Bayha KM, Chang MH, Mariani CL, Richardson JL, Edwards DL, DeBoer TS, et al., 2014. Worldwide phylogeography of the invasive ctenophore *Mnemiopsis leidyi* (Ctenophora) based on nuclear and mitochondrial DNA data. Biological Invasions. 2014;17(3): 1-24. doi: 10.1007/s10530-014-0770-6

Berline L, Stemmann L, Vichi M, Lombard F, Gorsky G., 2011. Impact of appendicularians on detritus and export fluxes: a model approach at DyFAMed site. J Plankton Res. 2011;33: 855-872.

Berline L, Zakardjian B, Molcard A, Ourmières Y, Guihou K., 2013. Modeling jellyfish *Pelagia noctiluca* transport and stranding in the Ligurian Sea. Mar Pollut Bull. 2013;70: 90-99.

Boero F., 2013. Review of jellyfish blooms in the Mediterranean and Black Sea. GFCM Studies and Reviews. 2013; 92: 53 pp.

Boero F, Putti M, Trainito E, Prontera E, Piraino S, Shiganova T., 2009. Recent changes in Western Mediterranean Sea biodiversity: the establishment of *Mnemiopsis leidyi* (Ctenophora) and the arrival of Phyllorhiza punctate (Cnidaria). Aquat Invasions. 2009;4: 675-680.

Boersma M, Malzahn A, Greve W, Javidpour J., 2007. The first occurrence of the ctenophore *Mnemiopsis leidyi* in the North Sea. Helgol Mar Res. 2007;61: 153-155.

Bolte S, Fuentes V, Haslob H, Huwer B, Thibault-Botha D, Angel D, et al., 2013. Population genetics of the invasive ctenophore *Mnemiopsis leidyi* in Europe reveal source-sink dynamics and secondary dispersal to the Mediterranean Sea. Mar Ecol Prog Ser. 2013;485: 25-36.

Brown J, Hill AE, Fernand L, Horsburgh KJ., 1999. Observations of a seasonal jet-like circulation at the central North Sea cold pool margin. Estuar Coast Shelf Sci. 1999;48(3): 343-355. doi:10.1006/ecss.1999.0426.

Buskey, E. J., 1993. Annual pattern of micro- and mesozooplankton abundance and biomass in a subtropical estuary. Journal of Plankton Research 15: 907-924.

Collingridge K, Van der Molen J, Pitois S., 2014. Modelling risk areas in the North Sea for blooms of the invasive comb jelly *Mnemiopsis leidyi* A. Agassiz, 1865. Aquat. Invasions. 2014;9(1): 21–36. doi: http://dx.doi.org/10.3391/ai.2014.9.1.02

Costello JH, Sullivan B. K, Gifford DJ, Van Keuren D, Sullivan LJ., 2006. Seasonal refugia, shoreward thermal amplification, and metapopulation dynamics of the ctenophore *Mnemiopsis leidyi* in Narragansett Bay, Rhode Island. Limnol Oceanogr. 2006;51: 1819-1831.

Costello JH, Bayha KM, Mianzan HW, Shiganova TA, Purcell JE., 2012. Transitions of *Mnemiopsis leidyi* (Ctenophora: Lobata) from a native to an exotic species: a review. Hydrobiologia. 2012;690: 21-46.

Cruz J, Morais P, Mocuba JJ, Baptista V, Cerveira I, Pereira V, et al., in press. The inevitable invasion of Portuguese estuarine ecosystems by the ctenophore *Mnemiopsis leidyi* A. Agassiz 1865. BioInvasions Rec.

Delpy F, Pagano M, Blanchot J, Carlotti F, Thibault-Botha D., 2012. Man-induced hydro-logical changes, metazooplankton communities and invasive species in the Berre Lagoon (Mediterranean Sea, France). Mar Pollut Bull. 2012;64(9): 1921-1932.
115

116

117

Delpy F, Albouy-Boyer S, Pagano M, Thibault D, Blanchot J, Guilhaumon F, et al., 2016. Identifying the drivers of abundance and size of the invasive ctenophore *Mnemiopsis leidyi* in Northwestern Mediterranean lagoons. Mar Environ Res. 2016;119: 114-125.

118

119

120

121

Diciotti R, Culurgioni J, Serra S, Trentadue M, Chessa G, Satta CT, et al., 2016. First detection of *Mnemiopsis leidyi* (Ctenophora, Bolinopsidae) in Sardinia (S'Ena Arrubia Lagoon, Western Mediterranean): a threat for local fishery and species recruitment. Mediterr Mar Sci. 2016;17(3):714-719. doi: http://dx.doi.org/10.12681/mms.1719

122

123

Dobrovolskii AD, Zalogin BS., 1982. Seas of the USSR. Moscow State University Publishing. 192 pp. 1982 (in Russian).

124

125

126

Dudkin SI, Logichevskaya TV, Mirzzoyan ZA., 2001. Metabolism ctenophore *Mnemiopsis leidyi* in the Sea of Azov and ecological effect from its invasion. VIII congress of Hydrobiological komission RAS. V.II. Kaliningrad, 17-21 September, 2001. pp. 75-76.

127

128

Dumont H.J., 1998. The Caspian Lake: History, biota, structure and function. Limnology and Oceanography 43: 44-52.

129

130

131

Dumoulin E., 2007. De Leidyi's ribkwal (*Mnemiopsis leidyi* A. Agassiz, 1865) al massaal in het havengebied Zeebrugge-Brugge, of: exoten als de spiegel van al te menselijk handelen. Strandvlo 27: 44-60.

132

133

El-Shabrawy G, Dumont HJ. 2009. The Fayum depression and its lakes. In: The Nile: origin, environments, limnology and human use. Springer, Dordrecht. 2009. Pp. 95-123.

134

135

136

El-Shabrawy G, Dumont HJ., 2016. First record of a ctenophore in lakes: the comb-jelly Mnemiopsis: invades the lakes of the Fayum, Egypt! BioInvasions Rec. 2016;5(1): 21-24. doi: http://dx.doi.org/10.3391/bir.2016.5.1.04

137

138

139

Esser M, Greve W, Boersma M., 2004. Effects of temperature and the presence of benthic predators on the vertical distribution of the ctenophore *Pleurobrachia pileus*. Marine Biology. 2004;145: 595-601. doi:10.1007/s00227-004-1348-0

140

141

Faasse MA Bayha K M., 2006. The ctenophore *Mnemiopsis leidyi* A. Agassiz 1865 in coastal waters of the Netherlands: an unrecognized invasion. Aquat Invasions. 2006;1: 270-277.

142

143

144

145

Finenko GA, Romanova ZA, Abolmasova GI, Anninsky BE, Svetlichny LS, Hubareva ES, et al., 2003. Population dynamics, ingestion, growth and reproduction rates of the invader *Beroe ovata* and its impact on plankton community in Sevastopol Bay, the Black Sea. J Plankton Res. 2003; 25: 539-549.

146

147

148

Ferraris M, Berline L, Lombard F, Guidi L, Elineu A, Mendosa-Vera JM, et al., 2012. Distribution of *Pelagia noctiluca* (Cnidaria, Scyphozoa) in the Ligurian Sea (NW Mediterranean Sea). J Plankton Res. 2012;34: 874-885.

149

150

151

Frolenko LN., 2006. Assesment of bottom biocenoses in the Sea of Azov. Collection of articles of AzNIIRKH. «The main problems of fishery and conservation of water bodies of Azov-Black Sea basin (20010-2012 rr.). Rostov-on-Don. 2006. pp. 77-88 (in Russian).

152

153

Fuentes V.L, Atienza D, Gili JM, Purcell JE., 2009. First records of *Mnemiopsis leidyi* A. Agassiz 1865 off the NW Mediterranean coast of Spain. Aquat Invasions. 2009;4: 671-674.

154

155

Fuentes V.L, Angel DL, Bayha KM, Atienza D, Edelist D, Bordehore C, et al., 2010. Blooms of the invasive ctenophore, Mnemiopsis leidyi, span the Mediterranean Sea in 2009. Hydrobiologia. 2010; 645: 23-37.

156

157

Galil BS., 2007. Seeing red: Alien species along the Mediterranean coast of Israel (2007). Aquat Invasions. 2007;2(4): 281-312.

158

159

Galil B, Gevili R., 2013. A moveable feast: *Beroe cucumis* sensu Mayer, 1912 (Ctenophora; Beroida; Beroidae) preying on *Mnemiopsis leidyi* A. Agassiz, 1865 (Ctenophora; Lobata; Bolinopsidae) off the Mediterranean coast of Israel. BioInvasions Rec. 2013;2(3): 191-194.

160

161

Galil BS, Kress N, Shiganova T., 2009. First record of *Mnemiopsis leidyi* A. Agassiz, 1865 (Ctenophora; Lobata; Mnemiidae) off the Mediterranean coast of Israel. Aquat Invasions. 2009; 4(2): 356-362.

162

163

Galil B, Gevili R, Shiganova T., 2011. Not far behind: First record of *Beroe ovata* Mayer, 1912 (Ctenophora: Beroida: Beroidae) off the Mediterranean coast of Israel. Aquat Invasions. 2011; 6 (Supplement 1): 89-S90. doi: 10.3391/ai.2011.6.S1.020

164
167

Galil B.S., Marchini A, Occhipinti-Ambrogi A., 2018. Mare Nostrum, Mare quod invaditur – the history of bioinvasions in the Mediterranean Sea. pp. 21-49. Queiroz A, Pooley S (Editors). Histories of Bioinvasions in the Mediterranean. Environmental History, vol 8. Springer. 2018. pp. 21-49.

168

169

170

Gaudy R, Vicas MD., 1985. Premiere signalisation en Mediterranee du copepode pelagique Acartia tonsa. CIESM Rapp. Comm. Int. Mer Medit. 1985;29: 227-229.

171

172

GESAMP (IMO/FAO/UNESCO-IOC/WMO/WHO/IAEA/UN/UNEP Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection), 1997. Opportunistic settlers and the problem of the ctenophore Mnemiopsis leidyi invasion in the Black Sea. Rep Stud GESAMP. 58: 84 pp.

173

174

175

176

Ghabooli S, Shiganova TA, Zhan A, Cristescu M, Eghtesadi-Araghi P, MacIsaac H., 2011. Multiple introductions and invasion pathways for the invasive ctenophore Mnemiopsis leidyi in Eurasia. Biological Invasions. 2011;13(3): 679-690. doi: 10.1007/s10530-010-9859-8

177

178

179

Ghabooli S, Shiganova TA, Briski E, Piraino S, Fuentes V, Thibault-Botha D, et al., 2013. Invasion pathway of the ctenophore *Mnemiopsis leidyi* in the Mediterranean Sea. PLoS One. 2013;8: e81067

180

181

Giani M, Djakovac T, Degobbis D, Cozzi S, Solidoro C, Fonda Umani S., 2012. Recent changes in the marine ecosystems of the northern Adriatic Sea. Estuar Coast Shelf Sci. 2012; 115: 1-13.

182

183

Gomoiu MT, Skolska M., 1996. Changements recents dans la biodiversite de la Mer Noire dus aux immigrants. GEO-ECO-MARINA, RCGGM.v.1. Danube delta-Black Sea system under global changes impact. Bucuresti. Constanta. 1996;1: 49-65.

184

185

186

Greve, W. (1975) Ctenophora. Fiches d'Identification du Zooplancton 146. Conseil International pour l'Exploration de la Mer, 6 pp.

187

188

Gubanova A.A. 2000. Occurrence of Acartia tonsa Dana in the Black Sea. Was it introduced from the Mediterranean? Mediterranean Marine sciences. V.1/1:105-110.

189

190

Gülşahin N., 2013. Abundance, Distribution and Biomass of Syphozoa (Cnidaria) and Ctenophora Species in the Neritic Area of Muğla. Ph.D Thesis. Muğla Sıtkı Koçman University, Faculty of Fisheries. 2013.

191

192

193

Gülşahin N, Tarkan AN., 2014. Seasonal distribution of Scyphozoa (Cnidaria) and Ctenophora species in Gökova Bay, Mugla, Turkey. Rapp. Comm. int. Mer Médit. 2013;40: 538.

194

195

Hansson HG, 2006. Ctenophores of the Baltic and adjacent Seas – the invader Mnemiopsis is here! Aquat Invasions. 2006;1: 295-298.

196

197

Haraldsson M, Jaspers C, Tiselius P, Aksnes DL, Andersen T, Titelman J., 2013. Environmental constraints of the invasive Mnemiopsis leidyi in Scandinavian waters. Limnol Oceanogr. 2013; 58: 37-48.

198

199

Harbison GR, Madin LP, Swanberg NR., 1978. On the natural history and distribution of oceanic ctenophores. Deep Sea Res. 1978;25 : 233-256.

200

201

Harding, LW, Degobbis D, Precali R., 1999. Production and Fate of Phytoplankton: Annual Cycles and Interannual Variability. Malone TS, Malej A, Harding LW, Smodlaka N, Turner RE (Editors) Ecosystems at the Land-Sea Margin: Drainage Basin to Coastal Sea. Coastal and Estuarine Studies. 1999;55: 131-172.

202

203

204

205

Herut B, Shefer E, Gordon N, Galil B, Tibor G, Tom M, et al., 2011. Environmental quality of Israel's Mediterranean coastal waters in 2010, IOLR. Report H68/2015. 2011.

206

207

Hosia A, Titelman J, Lars Johan Hansson LJ, Haraldsson M., 2011. Interactions between native and alien ctenophores: *Beroe gracilis* and *Mnemiopsis leidyi* in Gullmarsfjorden. MEPS. 2011;422: 129-138.

208

209

Hosia A, Falkenhaug T., 2013. Invasive ctenophore *Mnemiopsis leidyi* in Norvey. Fourth International Jellyfish Bloom Symposium. 5-7 June, 2013. Hiroshima, Japan.

210

211

Huwer B, Paulsen MR, Riisgard HU, Haslob H., 2008. Abundance, horizontal and vertical distribution of the invasive ctenophore *Mnemiopsis leidyi* in the central Baltic Sea, November 2007. Aquat. Invasions. 2008;3: 113-124.

212

213

214

Isinibilir M., 2011. Distribution of Gelatinous Zooplankton in the Southern Marmara Sea during 2006-2007. Turan C, and Özturk B (Editors). First National Workshop on Jellyfish and Other Gelatinous Species in Turkish Marine Waters. Published by Turkish Marine Research Foundation, Istanbul, TURKEY, 2011. Publication number: 35, pp. 34-42.

215

216

217

218

Isinibilir M, Tarkan AN., 2001. Abundance and distribution of Mnemiopsis leidyi in the northern Marmara Sea. Rapports de la Commission internationale pour la Mer Méditerranée. 36. CIESM, Monte-Carlo. 2001. 276 pp.

219

220
221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

Isinibilir M, Tarkan AN, Kideys AE., 2004. Decreased levels of the invasive ctenophore Mnemiopsis in the Sea of Marmara in 2001. In Aquatic Invasions in the Black, Caspian and Mediterranean Seas, pp. 155-165. Ed. Dumont H, Shiganova TA, Niermann U (Editors). Kluwer Academic Publishers, Dordrecht, the Netherlands. 2004.

Isinibilir M., 2012. The seasonal occurrence and abundance of gelatinous macrozooplankton in Izmit Bay (the northeastern Marmara Sea). J Black Sea Mediterr Environ. 2012;18(2): 155-176.

Isinibilir M, Okyar M, Ustun F, Orun DA., 2015. Changes in abundance and community structure of zooplankton population during the 2008 mucilage event in the northeastern Marmara Sea. Turkish Journal of Zoology. 2015;39: 29-38.

Iudicone D, Nardelli B, Santoleri R, Marullo S., 2003. Distribution and mixing of intermediate water masses of the Channel of Sicily (Mediterranean Sea). J Geophys Res. 2003;108 (C9): 8105.

Ivanov VP, Kamakin AM, Ushivtsev VB, Shiganova TA, Zhukova OP, Aladin N, Wilson SI, Harbison GR and Dumont HJ (2000). Invasion of the Caspian Sea by the comb jellyfish *Mnemiopsis leidyi* (Ctenophora). Biological Invasions. 2000;2: 255-258.

Janas U, Zgrundo A., 2007. First record of Mnemiopsis leidyi A. Agassiz, 1865 in the Gulf of Gdañsk (southern Baltic Sea). Aquat Invasions. 2007;2: 450-454.

Jaspers C, Møller LF, Kiørboe T., 2011. Salinity gradient of the Baltic Sea limits the reproduction and population expansion of the newly invaded comb jelly *Mnemiopsis leidyi*. PLoS One. 2011;6: e24065-e24065.

Jaspers C, Haraldsson M, Bolte S, Reusch TBH, Thygesen UH, Kiørboe T., 2012. Ctenophore population recruits entirely through larval reproduction in the central Baltic Sea. Biol Lett. 2012; 8: 809-12.

Jaspers C, Haraldsson M, Lombard F, Bolte S, Kiørboe T., 2013. Seasonal dynamics of early life stages of invasive and native ctenophores give clues to invasion and bloom potential in the Baltic Sea. J Plankton Res. 2013; 35: 582-594.

Jaspers C, Møller LF, Kiørboe T., 2015. Reproduction rate under variable food conditions and starvations in Mnemiopsis leidyi: significance for the success of a ctenophore. J Plankton Res. 2015;37: 1011-1018.

Jaspers C, Huwer B, Antajan E, Hosia A, Hinrichsen HH, Biastoch A, et al., 2018. Ocean current connectivity propelling the secondary spread of a marine invasive comb jelly across western Eurasia. Glob Ecol Biogeogr. 2018;1-14. doi: 10.1111/geb.12742

Javidpour J, Sommer U, Shiganova TA., 2006. First record of Mnemiopsis leidyi in the Baltic Sea. Aquat Invasions. 2006;1: 299-302.

Javidpour J, Molinero JC, Lehmann A, Hansen T, Sommer U., 2009a. Annual assessment of the predation of *Mnemiopsis leidyi* in a new invaded environment, the Kiel Fjord (Western Baltic Sea): a matter of concern? J Plankton Res. 2009;31(7): 729-738.

Javidpour J, Molinero JC, Peschutter J, Sommer U., 2009b. Seasonal changes and population dynamics of the ctenophore *Mnemiopsis leidyi* after its first year of invasion in the Kiel Fjord, Western Baltic Sea. Biol Invasions 2009;11: 873-882.

Johansson M. L., Shiganova T. A., Ringvold H., Stupnikova A. N., Heath D. D., and MacIsaac H. J. 2018. Molecular Insights Into the Ctenophore Genus *Beroe* in Europe: New Species, Spreading Invaders. Journal of Heredity, 520-529 doi:10.1093/jhered/esy026

Kamakin AM, Chigenkova OA, Zaitsev VF., 2010. Comprehensive research of *Mnemiopsis leidyi* population in the Caspian Sea in 2009. Biodiversity of the Caspian Sea and its Coastal Ecosystems. 2010;4: 50-59.

Kamburska L, Schrimpf W, Djavidnia S, Shiganova T, Stefanova K., 2006. Special focus on the ctenophore *Mnemiopsis leidyi* Agassiz, 1865 in the Black Sea. Addressing the ecological issue of the invasive species. European commission. Joint Research Center. Scientific and Technical Research series. 2006. 59 pp.

Kasymov AG., 1987. Biota of the Caspian Sea. Baku: ELM. 1987. 156 pp. (in Russian).

Khlebovich VV., 1974. Critical salinity of biological processes. Leningrad. Nauka. 1974. 235 pp.

Kideys AE, Niermann U., 1994. Occurrence of Mnemiopsis along the Turkish coast. ICES J Mar Sci. 1994;51: 423-427.

Kopelevich OV, Sheberstov SV, Sahling IV, Vazyulya SV, Burenkov VI. Atlas of bio-optical characteristics from satellite ocean color data of 1998-2012. 2014. CD-ROM.
275

276

277

278

279

280

281

282

283

284

285

286

287

288

289

290

291

292

293

294

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

324

325

326

Kosarev AN., 2006. Physico-Geographical Conditions of the Caspian Sea. The Caspian Sea Environment.

Kostianoy A, Kosarev A (Editors). Berlin/Heidelberg: Hdb Env. Chem. Part P. Springer-Verlag.

2006. pp. 5-32.

Kremer P., 1994. Patterns of abundance for Mnemiopsis in U.S. coastal waters: a comparative overview.

ICES J Mar Sci. 1994;51: 347-354.

Kube S, Postel L, Honnef C, Augustin CB., 2007. *Mnemiopsis leidyi* in the Baltic Sea-distribution and overwintering between autumn 2006 and spring 2007. Aquat Invasions. 2007;2: 137-145.

Lehmann A, Javidpour J (2010) Potential pathways of invasion and dispersal of Mnemiopsis leidyi A.

Agassiz 1865 in the Baltic Sea. Hydrobiologia 649(1):107-114. doi:10.1007/s/10750-010-0233-8

Lehtiniemi M, Lehmann A, Javidpour J, Myrberg K., 2011. Spreading and physico-biological reproduction limitations of the invasive American comb jelly *Mnemiopsis leidyi* in the Baltic Sea. Biol Invasions.

2011. doi: 10.1007/s10530-011-0066-z.

Lepparanta M, Myrberg K., 2009. Physical oceanography of the Baltic Sea. Springer, Berlin. 2009.

Lilley MKS, Thibault-Botha D, Lombard F., 2014. Respiration demands increase significantly with both temperature and mass in the invasive ctenophore *Mnemiopsis leidyi*. J Plankton Res. 2014;36: 831-837. doi: 10.1093/plankt/fbu008

Lonsdale, D. J., 1981. Regulatory role of physical factors and predation for two Chesapeake Bay copepod species. Marine Ecology Progress Series 5: 341-351

Macali A, Tiralongo F., 2018. On the occurrence of the sea walnut, *Mnemiopsis leidyi* Agassiz, 1865, in the

Fiora river (Italy). New Mediterranean Biodiversity Records (July 2018). Mediterr Mar Sci. 2018;19(2): 9.

doi: 10.12681/mms.18099

Malej A, Mozetič P, Malačič V, Terzić S, Ahel M., 1995. Phytoplankton responses to freshwater inputs in a small semi-enclosed gulf (Gulf of Trieste, Adriatic Sea). Mar Ecol Prog Ser. 1995;120: 111-121.

Malej A, Tirelli V, Lučić D, Paliaga P, Vodopivec M, Goruppi A, Shiganova TA., 2017. *Mnemiopsis leidyi* in the northern Adriatic: here to stay? J Sea Res. 2017;124: 10-16. doi: 10.1016/j.seares.2017.04.010

Marambio M, Franco I, Purcell JE, Canepa A, Guerrero E, Fuentes V., 2013. Aggregations of the invasive ctenophore *Mnemiopsis leidyi* in a hypersaline environment, the Mar Menor lagoon (NW Mediterranean). Aquat Invasions. 2013;8(2): 243-248.

Mianzan H., 1986. Beroe ovata en aguas de la bahía Blanca, Argentina (Ctenophora). Spheniscus. 1986, 2: 29-32.

Mianzan H. Ctenophora., 1999. In Boltovskoy D (Editor), South Atlantic Zooplankton. Backhuys Publishers, Leiden. 1999. pp. 561-573.

Mianzan H.W. et Sabatini M.L., 1985. Estudio preliminar sobre distribucíon y abendancia de Mnemiopsis mccradyi en el estuario de Bahna Blanca, Argentina (Ctenophora). Spheniscus. 1985, Nº 1. - P. 53-58.

Mianzan, H. W., N. Mari, B. Prenski & F. Sanchez, 1996. Fish predation on neritic ctenophores from the Argentine continental shelf: A neglected food resource? Fisheries Research 27: 69-79.

Mianzan, H.W., P. Martos, J. H. Costello & R. Guerro, 2010. Avoidance of hydrodynamically mixed environments by *Mnemiopsis leidyi* (Ctenophora: Lobata) in open-sea populations from Patagonia, Argentina. Hydrobiologia 645: 113-124.

Mirsoyan ZA, Volovik SP, Kornienko GG, Dudkin SI, Logichevskaya TV., 2000. Biology of the ctenophore *Mnemiopsis leidyi* in the Sea of Azov. In: ctenophore Mnemiopsis leidyi (A. Agassiz) in the Sea of Azov and the Black Sea: Biology and impact. Volovik SP (Editor). Rostov-on-Don. AzNIIRKH. 2000. pp. 101-144.

Mirsoyan ZA, Martynuk ML, Vayzun EV., 2006. Current pattern of ctenophores *Beroe ovata* and *Mnemiopsis leidyi* development in the Sea of Azov. Collection of articles of AzNIIRKH. «The main problems of fishery and conservation of water bodies of Azov-Black Sea basin (2004-2005). Rostov-on-Don. 2006. pp. 136-148 (in Russian).

Mordukhai-Boltovskoi FD., 1960. Caspian fauna in the Azov-Black Sea basin M. L. AN USSR. 1960. 288 pp.

Mutlu E., 1999. Distribution and abundance of ctenophores and their zooplankton food in the Black Sea. II. *Mnemiopsis leidyi*. Marine Biology. 1999;135(4): 603-614.
327

328

329

Mozetič P, France J, Kogovšek T, Talaber I, Malej A., 2012. Plankton trends and community changes in a coastal sea (northern Adriatic): Bottom-up vs. top-down control in relation to environmental drivers. Estuar Coast Shelf Sci. 2012;115: 138-148.

330

331

332

333

Nadolinsky VP, 2006. Assessment of ichthyoplankton of the Sea of Azov and the northeastern Black Sea and determined its factors at present time. Collection of articles of AzNIIRKH. «The main problems of fishery and conservation of water bodies of Azov-Black Sea basin (2010-2012 гг.). Rostov-on-Don. 2006. pp. 128-136 (in Russian).

334

335

336

Oguz T, Salihoglu B, Fach B., 2008. A coupled plankton-anchovy population dynamics model assessing nonlinear controls of anchovy and gelatinous biomass in the Black Sea. Mar Ecol Prog Ser. 2008;369: 229-256. doi: 10.3354/meps07540

337

338

Olenin S, Ojaveer H, Minchin D, Boelens R., 2016. Assessing exemptions under the ballast water management convention: preclude the Trojan horse. Mar Pollut Bull. 2016;103: 84-92.

339

340

341

Oliveira O.M.P., 2007. The presence of the ctenophore *Mnemiopsis leidyi* in the Oslofjorden and considerations on the initial invasion pathways to the North and Baltic Seas. Aquat Invasions. 2007; 2: 185-189.

342

343

344

Oliveira O.M.P., Miranda T. P., Araujo E. M., Ayón P., Cedeño-Posso C. M.; Cepeda-Mercado A. et al. Monograph Census of Cnidaria (Medusozoa) and Ctenophora from South American marine waters 2016. 4194 (1): 001-256

345

346

Olson, M. M., 1987. Zooplankton. In Heck, K. L., Jr. (ed.), Ecological Studies in the Middle Reach of Chesapeake Bay. Springer-Verlag, New York: 38-81

347

348

Paavola M, Olenin S, Leppakoski E., 2005. Are invasive species most successful in habitats of low native species richness across European brackish water seas? Estuar Coast Shelf Sci. 2005;64: 738-750.

349

350

351

352

Pagès F., 2001. Past and present anthropogenic factors promoting the invasion, colonization and dominance by jellyfish of a Spanish coastal lagoon. Briand F (Editor). 2001 CIESM Gelatinous zooplankton outbreaks: theory and practice. Naples, Italy, August 29 – September 1, 2001. CIESM Workshop Series 14, pp. 69-71.

353

354

355

Pasternak AF., 1983. Sesonal dynamic abundance and biomass of zooplankton in the coastal waters of the north Caucases. Sesonal changes of the Black Sea plankton. Sorokin YI, Vedernikov VI (Editors). Nauka, 1983. pp. 139-177 (in Russian).

356

357

Pereladov MV., 1988. Some observations for biota of Sudak Bay of the Black Sea. III All-Russian conference of marine biology. Naukova Dumka, Kiev. 1988. pp. 237-238 (in Russian).

358

359

360

Pérez-Ruzafa A, Quispe-Becerra JI, García-Charton JA, Marcos C., 2004. Composition, structure and distribution of the ichthyoplankton in a Mediterranean coastal lagoon. J Fish Biol. 2004;64: 202-218. http://dx.doi.org/10.1111/j.1095-8649.2004.00301.x

361

362

Purcell JE, Shiganova TA, Decker MB, Houde ED., 2001. The ctenophore *Mnemiopsis* in native and exotic habitats: U.S. estuaries versus the Black Sea basin. Hydrobiologia. 2001;451: 145-176.

363

364

365

Qiu ZF, Doglioli AM, Hu ZY, Marsaleix P, Carlotti F., 2010. The influence of hydrodynamic processes on zooplankton transport and distributions in the North Western Mediterranean: Estimates from a Lagrangian model. Ecol Modell. 2010;221: 2816-2827.

366

367

368

Reaugh ML, Roman MR, Stoecker DK., 2007. Changes in plankton community structure and function in response to variable freshwater flow in two tributaries of the Chesapeake Bay. Estuaries Coast. 2007;30(3): 403-417.

369

370

371

Reeve MR, Syms MA, Kremer P., 1989. Growth dynamics of a ctenophore (*Mnemiopsis*) in relation to variable food supply. I. Carbon biomass, feeding, egg production, growth and assimilation efficiency. J Plankton Res. 1989;11(3): 535-552.

372

373

374

Reusch T, Bolte S, Sparwell M, Moss A, Javidpour J., 2010. Microsatellites reveal origin and genetic diversity of Eurasian invasions by one of the world's most notorious marine invader, *Mnemiopsis leidyi* (Ctenophora). Mol Ecol. 2010;19: 2690-2699.

375

376

Riisgård HU., 2017. Invasion of Danish and Adjacent Waters by the Comb Jelly *Mnemiopsis leidyi* - 10 Years After. Open J Mar Sci. 2017;7: 458-471.

377

378

Riisgård HU, Goldstein J., 2014. Jellyfish and Ctenophores in Limfjorden (Denmark)—Mini-Review, with Recent New Observations. J Mar Sci Eng. 2014;2(4): 593-615.
379

380

381

382

383

384

385

386

387

388

389

390

391

392

393

394

395

396

397

398

399

400

401

402

403

404

405

406

407

408

409

410

411

412

413

414

415

416

417

418

419

420

421

422

423

424

425

426

427

428

429

430

431

432

Riisgård HU, Barth-Jensen C, Madsen CV., 2010. High Abundance of the Jellyfish *Aurelia aurita* Excludes the Invasive Ctenophore *Mnemiopsis leidyi* to Establish in a Shallow Cove (Kertinge Nor, Denmark). Aquat Invasions. 2010;5: 347-356. https://doi.org/10.3391/ai.2010.5.4.03

Ringvold H, Shiganova TA, Knott KE, Galil BS., 2015. First record of *Beroe gracilis* Künne, 1939 (Ctenophora; Beroida; Beroidae) from Norway, in a *Mnemiopsis leidyi* A. Agassiz, 1865 bloom. Mar Biodivers Rec. 2015;8: 1-5. doi: 10.1017/S1755267215000366

Roohi A, Kideys A, Sajjadi A, Hashemian A, Pourgholam R, Fazli H, et al., 2010. Changes in biodiversity of phytoplankton, zooplankton, fishes and macrobenthos in the Southern Caspian Sea after the invasion of ctenophore Mnemiopsis leidyi. Biol Invasions. 2010;2: 2343-2361. doi: 10.1007/s10530-009-9648-4.

Rogov S.F., Lutz G.I., Volovik S.P. 2000. Biology and adaptation Anchovy and KIIka after invasion ctenophore M.leidyi. Ctenophore Mnemiopsis leidyi in the Sea of Azov and the Black Sea Ed.Volovik S.P. Rostov -on-Don. AzNIIRKH: 234-294.

Salat J, Garcia MA, Cruzado A, Palanques A, Arín L, Gomis D, et al., 2002. Seasonal changes of water mass structure and shelf slope exchanges at the Ebro shelf (NW Mediterranean). Cont Shelf Res. 2002; 22: 327-346. doi:10.1016/S0278-4343(01)00031-0

Schaber M, Haslob H, Huwer B, Harjes A, Hinrichsen H, Koster FW, et al., 2011. The invasive ctenophore *Mnemiopsis leidyi* in the central Baltic Sea: seasonal phenology and hydrographic influence on spatio-temporal distribution patterns. J Plankton Res. 2011; 33 (7): 1053-1065.

Seebens H, Briski E., Ghabooli S, Shiganova T., MacIsaac H. J. and Blasius B. 2019. Non-native species spread in a complex network: the interaction of global transport and local population dynamics determines invasion success. Proc. R. Soc. 286: 20190036. http://dx.doi.org/10.1098/rspb.2019.0036

Shiganova TA., 1993. Ctenophore *Mnemiopsis leidyi* and ichthyoplankton in the Sea of Marmara in October of 1992. Oceanology. 1993;33: 900-903.

Shiganova TA., 1997. *Mnemiopsis leidyi* abundance in the Black Sea and its impact on the pelagic community. In: Sensivity to Change: Black Sea, Baltic Sea and North Sea. Ozsoy E, A. Mikaelyan A (Editors). Kluwer Ac. Pub.NATO ASI Series.1997. pp. 117-131.

Shiganova TA., 1998. Invasions of the Black Sea by the ctenophore *Mnemiopsis leidyi* and recent changes in pelagic community structure. Fish Oceanogr.1998;7: 305-310.

Shiganova TA., 2009. Non-native species in the Seas of Eurasia. D.Sci. Thesis. A. N. Severtsov Institute of Ecology and Evolution. 2009. 643 pp. Available from: http://www.sevin.ru/dissertations/gidrobiol/49.pdf

Shiganova T., 2010. Biotic Homogenization of Inland Seas of the Ponto-Caspian. Annu Rev Ecol Evol Syst. 2010;41: 103-126.

Shiganova TA., 2011. Review of the status of invasive species with special focus on the most invasive species *Mnemiopsis leidyi* (A.Agassiz, 1865) and their effect on the Caspian ecosystem. CASPECO.123 pp.

Shiganova TA, Bulgakova YV., 2000. Effect of gelatinous plankton on the Black and Azov Sea fish and their fish resources. ICES J Mar Sci. 2000;57: 641-648.

Shiganova TA, Malej A., 2009. Native and non-native ctenophores in the Gulf of Trieste, northern Adriatic Sea. J Plankton Res. 2009;31(1): 62-72.

Shiganova TA, Bulgakova YV, Volovik SP, Mirzoyan ZA, Dudkin SI., 2001a. A new invader, *Beroe ovata* Mayer 1912 and its effect on the ecosystems of the Black and Azov Seas. Hydrobiologia. Purcel JE, W. M. Graham WM, H.J. Dumont HJ (Editors). Kluwer Ac. Pub. 2001;451. pp. 87-197.

Shiganova TA, Mirzoyan ZA, Studenikina EA, Volovik SP, Siokou-Frangou I, Zervoudaki S, et al., 2001b. Population development of the invader ctenophore *Mnemiopsis leidyi* in the Black Sea and other seas of the Mediterranean basin. Mar Biol. 2001. pp. 431-445.

Shiganova TA, Sapognikov VV, Musaeva EI, Domanov MM, Bulgakova YV, et al., 2003. Factors that determine pattern of distribution and abundance *Mnemiopsis leidyi* and its effect on ecosystem in the Northern Caspian. Oceanology. 2003;43(5): 716-733.

Shiganova TA, Dumont HJ, Mikaelyan A, Glazov DM, Bulgakova YV, Musaeva EI, et al., 2004a. Interaction between the invading ctenophores *Mnemiopsis leidyi* A. Agassiz and *Beroe ovata* Mayer 1912, and their Influence on the pelagic ecosystem of the northeastern Black Sea. Dumont H,
Shiganova TA, Niermann U (Editors). The Ctenophore *Mnemiopsis leidyi* in the Black, Caspian and Mediterranean Seas and Other Aquatic Invasions. NATO Science Series: IV. Earth and Environmental Sciences. Vol. 35. Kluwer Academic Publishers, Dordrecht. 2004:35. pp. 33-70.

Shiganova TA, Dumont HJ, Sokolsky AF, Kamakin AM, Tinenkova D, Kurasheva EK., 2004b. Population dynamics of *Mnemiopsis leidyi* in the Caspian Sea, and effects on the Caspian ecosystem. Dumont H, Shiganova TA, Niermann U (Editors). The Ctenophore *Mnemiopsis leidyi* in the Black, Caspian and Mediterranean Seas and other aquatic invasions. NATO ASI Series: 2. Environment. Kluwer Acad. Pub. 2004. pp. 71-111.

Shiganova T, Christou ED, Bulgakova JV, Siokou-Frangou I, Zervoudaki S, Siapatis A., 2004c. Study on the distribution and biology of the invader *M. leidyi* in the northern Aegean Sea, comparison with indigenous species *Bolinopsis vitrea*. Dumont H, Shiganova TA, Niermann U (Editors). The Ctenophore *Mnemiopsis leidyi* in the Black, Caspian and Mediterranean Seas and other aquatic invasions. NATO ASI Series: 2. Environment. Kluwer Acad. Pub. 2004. pp. 113-135.

Shiganova TA, Christou ED, Siokou-Frangou I., 2007. First finding of alien species *Beroe ovata* Mayer 1912 in the Aegean Sea. Mediterr Mar Sci 2007;8(1): 5-14.

Shiganova TA, Legendre L, Kazmin AS, Nival P., 2014a. Interactions between invasive ctenophores in the Black Sea: assessment of control mechanisms based on long-term observations. Mar Ecol Prog Ser. 2014;507: 111-123

Shiganova TA, Riisgård HU, Ghabooli S, Tendal OS., 2014b. First report on *Beroe ovata* in an unusual mixture of ctenophores in the Great Belt (Denmark). Aquat Invasions. 2014;9(1): 111-116.

Shiganova TA, Alekseenko E, Moskalenko L, Nival P., 2018. Modelling assessment of interactions in the Black Sea of the invasive ctenophores *Mnemiopsis leidyi* and *Beroe ovata*. Ecol Modell. 2018;376: 1-14. doi.org/10.1016/j.ecolmodel.2018.02.008

Shiganova T.A., Alekseenko E., Kazmin A.S., 2019. Predicting range expansion of invasive ctenophore *Mnemiopsis leidyi* A. agassiz 1865 under current environmental conditions and future climate change scenarios. Estuarine, Coastal and Shelf Science. 2019. https://doi.org/10.1016/j.ecss.2019.106347

Siapatis A, Giannoulaki M, Valavanis VD, Machias A, Somarakis S., 2010. Spatial distribution of ctenophore *Mnemiopsis leidyi* in Aegean Sea. Rapp Comm Int Mer Medit. 2010;39: 665.

Siokou-Frangou I, Shiganova T, Christou E, Gubanova A, Kamburska L, Konsulov A, et al., 2004. Mesoplankton communities in the Aegean and the Black Seas: a comparative study. Mar Biol. 2004;144: 1111-1128.

Siokou-Frangou I, Christaki U, Mazzocchi MG, Montresor M, Ribera d'Alcal'a M, Vaqu'e D, et al., 2010. Plankton in the open Mediterranean Sea: a review. Biogeosciences. 2010;7(5): 1543-1586. doi:10.5194/bg-7-1543-2010

Sorarrain, D., 1998. Cambios estacionales en la biomasa de organismos gelatinosos en relación con otros zoopláncteres en la bahía Samborombo'n. MSc Thesis, Facultad de Ciencias Exactas y Naturales, Departamento de Ciencias Marinas, Universidad Nacional de Mar del Plata, Argentina, Mar del Plata: 35 pp.

Studenikina EI, Volovik SP, Miryozan IA, Luts GI., 1991. The ctenophore *Mnemiopsis leidyi* in the Sea of Azov. Oceanology. 1991;3: 722-725.

Tarkan AN, Isinibilir M, Ogdul RG., 2000. Mesozooplankton composition Sea of northern Marmara. Oztürk B, Kadioglu M, Oztürk H (Editors). Symposium on The Marmara Sea 2000 TUDAV. Istanbul. 2000. pp. 493-499. (in Turkish).

Tendal OS, Jensen KR, Riisgård HU., 2007. Invasive ctenophore *Mnemiopsis leidyi* widely distributed in Danish waters. Aquat Invasions. 2007;2: 272-277.

Tilves U, Purcell JE, Marambio M, Canepa A, Olariaga A, Fuentes V., 2013. Predation by the scyphozoan *Pelagia noctiluca* on *Mnemiopsis leidyi* ctenophores in the NW Mediterranean Sea. J Plankton Res. 2013;35: 218-224.

Van Ginderdeuren K, Hostens K, Hoffman S, Vansteenbrugge L, Soenen K, De Blauwe H, et al., 2012. Distribution of the invasive ctenophore *Mnemiopsis leidyi* in the Belgian part of the North Sea. Aquat Invasions. 2012;7(2): 163-169.

Van Walraven L, Langenberg VT, Van der Veer HW., 2013. Seasonal occurrence of the invasive ctenophore *Mnemiopsis leidyi* in the western Dutch Wadden Sea. J Sea Res. 82: 86-92.
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Vandromme P, Stemmann L, Berline L, Gasparini S, Mousseau L, Prejger F, et al., 2011. Interannual fluctuations of zooplankton communities in the Bay of Villefranche-sur-mer from 1995 to 2005 (Northern Ligurian Sea, France) Biogeosciences. 2011;8: 3143-3158. doi: 10.5194/bg-8-3143-2011

Vansteenbrugge L, Ampe B, De Troch M, Vincx M, Hostens K., 2015. On the distribution and population dynamics of the ctenophore *Mnemiopsis leidyi* in the Belgian part of the North Sea and Westerschelde estuary. Mar Environ Res. 2015;110: 33-44. doi: http://dx.doi.org/10.1016/j.marenvres.2015.07.011.

Velasco J, Lloret J, Millan A, Marin A, Barahona J, Abellan P, Sanchez-Fernandez D (2006) Nutrient and particulate inputs into the Mar Menor Lagoon (SE Spain) from an intensive agricultural watershed Water, Air and Soil Pollution 176: 37-56, http://dx.doi.org/10.1007/s11270-006-2859-8

Vinogradov ME, Shushkina EA, Musaeva IA, Sorokin PY., 1989. Ctenophore *Mnemiopsis leidyi* (A. Agassiz) (Ctenophora: Lobata) – new settlers in the Black Sea. Oceanology. 1989;29: 293-298.

Zaika VE., 2005. Where and how Black Sea population of the ctenophora *Mnemiopsis leidyi* is overwintering? Marine ecological J. 2005;4(1): 51-53.

Zaghloul W.S., Madkour F.F. and Mohammad S. H.Two first records of ctenophora (Pleurobrachia pileus and Mnemiopsis leidyi) from the Egyptian water of the Red Sea, Egypt.J. Oceanogrraphy and Marine Sciences. In press.
<table><thead><tr><th>AREA/MONTH</th><th>J</th><th>F</th><th>M</th><th>A</th><th>M</th><th>J</th><th>J</th><th>A</th><th>S</th><th>O</th><th>N</th><th>D</th><th>T°C</th><th>T°C,R</th><th>S</th><th>Z</th><th>References</th></tr></thead><tbody><tr><td>Black Sea (&lt;2006)</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>5-25</td><td>21-25</td><td>12-22</td><td>+</td><td>Shiganova et al., 2004</td></tr><tr><td>Black Sea (&gt;2006)</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>8-30</td><td>18-26</td><td>12-22</td><td>+</td><td>Shiganova et al., 2018</td></tr><tr><td>Sea of Azov</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>-0.8-30</td><td>18-26</td><td>6-14</td><td>+</td><td>Mirzoyan et al., 2006</td></tr><tr><td>Southern Caspian</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>10-30</td><td>10-30,5</td><td>12.6-13</td><td>+</td><td>Shiganova, 2011</td></tr><tr><td>Middle Caspian</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>5.8-26</td><td>18-26</td><td>12.1-12.6</td><td>+</td><td>Shiganova, 2011</td></tr><tr><td>Northern Caspian</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>3.8-28</td><td>23-27</td><td>6.1-10.0</td><td>+</td><td>Shiganova, 2011</td></tr><tr><td>Sea of Marmara</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>8-29</td><td>21-26</td><td>22-29</td><td>+</td><td>Isinibilir, 2012; Shiganova,1993</td></tr><tr><td>Northern Aegean</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>12-27</td><td>21-25</td><td>33-39</td><td>+</td><td>Siapatis, 2014</td></tr><tr><td>Southern Aegean</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>14.5-29</td><td>18-26.5</td><td>37.3-39.6</td><td>+</td><td>Gülşahin, 2013</td></tr><tr><td>Levantine Sea</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>17,5-31</td><td>19.5-23.5</td><td>39.3-40.0</td><td>ND</td><td>Galil pers.com.</td></tr><tr><td>Northern Adriatic</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>6-29</td><td>17-28</td><td>11-38</td><td></td><td>Malej et al., 2017</td></tr><tr><td>Legurian Sea</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1-27</td><td>17-21.9</td><td>37.9-38.2</td><td>+</td><td>Lilley, Lombard, Shiganova, unpublished</td></tr><tr><td>Catalan Coast</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>10-30</td><td>10-25</td><td>34-38</td><td>ND</td><td>Marambio pers.com.</td></tr><tr><td>Berre Lagoon</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>3,4-28.2</td><td>10-25.2</td><td>15.9-26.2</td><td>+</td><td>Delpy et al., 2016</td></tr><tr><td>Bages-Sigean</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>9,6-27,1</td><td>18-27</td><td>18.9-34.3</td><td>+</td><td>Delpy et al., 2016</td></tr><tr><td>Portugal coast</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>17.2-22.2</td><td>17.4-20</td><td>34.9-35.3</td><td>+</td><td>Crus et al, in press</td></tr><tr><td>Kiel Bight</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>3.5-22.2</td><td>13.1-22.2</td><td>14-20</td><td>+</td><td>Javidpour et al., 2009a</td></tr><tr><td>Danish Fjords</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>-0.5-24</td><td>12-24</td><td>19-34</td><td>+</td><td>Riisgård, et al., 2015-17</td></tr><tr><td>Central Baltic</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>2-20</td><td>8.4-10.7(>)</td><td>7.8±0.3</td><td>+</td><td>Jaspers et al. 2011,2013</td></tr><tr><td>Kattegat</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>0-21</td><td>11.±7-21</td><td>25±3</td><td>-</td><td>Jaspers et al. 2011;</td></tr></tbody></table>
<table><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>Haraldsson et al., 2013</td></tr><tr><td>Skagerrak</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>Haraldsson et al., 2013</td></tr><tr><td>Wadden Sea</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>Van Walraven et al., 2013</td></tr></table>

<figure><img src="image_19.png" /></figure>

<figure><img src="image_20.png" /></figure>

6-20

>9-20

25-29

-

1.7-22

18-21

34-35

ND

<figure><img src="image_21.png" /></figure>
<table><thead><tr><th>AREA/MONTH</th><th>J</th><th>F</th><th>M</th><th>A</th><th>M</th><th>J</th><th>J</th><th>A</th><th>S</th><th>O</th><th>N</th><th>D</th><th>T°C</th><th>T°C-R</th><th>S</th><th>Z</th><th>References</th></tr></thead><tbody><tr><td>Narragansett Bay, RI</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1-25</td><td>10-24</td><td>25-32</td><td>+</td><td>Costello et al., 2012</td></tr><tr><td>Mid Chesapeake Bay, MD</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>2-30</td><td>12-29</td><td>5-16</td><td>+</td><td>Lonsdale, 1981; Olson, 1987; Purcell et al., 1994</td></tr><tr><td>Biscayne Bay, FL</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>18-32</td><td>18-28</td><td>14-45</td><td>+</td><td>Baker, 1973</td></tr><tr><td>Nueces Estuary, TX</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>10-30</td><td>10-30</td><td>20-38</td><td>+</td><td>Buskey, 1993</td></tr><tr><td>Rio de la Plata estuary, ARG</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>7.5-25</td><td>10--25</td><td>9-24</td><td>+</td><td>Mianzan et al., 1996; Sorarrain, 1998</td></tr><tr><td>Blanca bay, ARG</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>5-24</td><td>10-24</td><td>24-38</td><td>+</td><td>Mianzan & Sabatini, 1985; Mianzan, 1986</td></tr><tr><td>Nord Patagonic Tidal front, ARG</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>10-16</td><td>10-16</td><td>33</td><td>+</td><td>Mianzan et al., 1996, 2010; Mianzan pers. obs</td></tr></tbody></table>
* Harmful invader *M. leidyi*'s expansions in the Eurasian Seas have been synthesized

* Ranges of sea surface temperature, salinity and chlorophyll values were assessed

* These ranges sufficient for *M. leidyi* occurrence and reproduction were used

* Two eco-types (Southern and Northern) in the recipient seas of Eurasia were revealed

* Thresholds in both eco-types depend on environmental parameters in native habitats

<figure><img src="image_22.png" /></figure>
<figure><img src="image_23.png" /></figure>