# Diversity and spatial variability of shallow benthic macrofaunal assemblages in a high-Arctic fjord (Young Sound, North-East Greenland)

Guillaume Bridier, Frédéric Olivier, Lucas Pinsivy, Jérôme Jourde, Laurent

Chauvaud, Mikael Sejr, Thomas Burel, Michel Le Duff, Jacques Grall

► To cite this version:

Guillaume Bridier, Frédéric Olivier, Lucas Pinsivy, Jérôme Jourde, Laurent Chauvaud, et al. Diversity and spatial variability of shallow benthic macrofaunal assemblages in a high-Arctic fjord (Young Sound, North-East Greenland). Polar Biology, 2024, 10.1007/s00300-024-03235-y. http://hal-04533690

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1 TITLE: Diversity and spatial variability of shallow benthic macrofaunal assemblages in
2 a high-Arctic fjord (Young Sound, North-East Greenland)

3
4 Guillaume Bridier¹,², Frédéric Olivier³, Lucas Pinsivy¹, Jérôme Jourde⁴, Laurent
5 Chauvaud¹, Mikael K. Sejr⁵, Thomas Burel¹, Michel Le Duff⁶, Jacques Grall¹,⁶

6
7 Research article submitted to *Polar Biology*.

8
9
10 ¹Laboratoire des Sciences de l'Environnement Marin (LEMAR) UMR 6539
11 UBO/CNRS/IRD/Ifremer, rue Dumont D'Urville, 29280 Plouzané, France
12 ²Present Address: Institut des Sciences de la mer de Rimouski, Université du Québec à
13 Rimouski, 310 allée des Ursulines, QC G5L 2Z9 Rimouski, Canada

14 ³Biologie des Organismes et Ecosystèmes Aquatiques (BOREA) UMR 7208
15 MNHN/SU/UA/CNRS/IRD, 61 Rue Buffon CP53, 75005 Paris, France

16 ⁴OBIONE (Observatoire de la Biodiversité Faune Flore des Pertuis Charentais) UMR 7266
17 LIENS CNRS/Université de La Rochelle, 2 rue Olympe de Gouges, 17000 La Rochelle,
18 France

19 ⁵Department of EcoScience & Arctic Research Centre, Aarhus University, C.F. Møller Alle 3,
20 bld. 1131, 8000 Aarhus, Denmark

21 ⁶Observatoire Marin, UMS 3113, Institut Universitaire Européen de la Mer, rue Dumont
22 D'Urville, 29280 Plouzané, France

23
24
25 Corresponding author: Guillaume Bridier (guillaume.bridier@live.ie)

26
27

**Abstract**

Although knowledge of Arctic benthic biodiversity has increased considerably in recent decades, some regions, such as Northeast Greenland, remain poorly studied. The aim of this study was to complement a previous macrofaunal inventory carried out in Young Sound, a High-Arctic fjord in this region (74°N). We sampled shallow benthic assemblages along a small inner/outer fjord gradient, including one station previously prospected two decades ago and three new stations. This sampling strategy revealed highly diversified benthic assemblages (166 species identified on a total sampling area of 1.32 m²), which considerably increases the number of species recorded for the fjord (i.e. 225 species vs 100 previously recorded). The outermost station was dominated in abundance by various assemblages of bivalves, while the middle stations showed greater species evenness, including numerous species of polychaetes, bivalves and crustaceans. The innermost station was dominated by ostracods, gammarid amphipods and tube-dwelling polychaetes. Overall, benthic assemblages varied little between the four stations and the transect as a whole exhibited characteristics typical of outer fjord habitats, reflecting the rather moderate impact of meltwater inputs in this part of the fjord. Finally, trophic plasticity and omnivory were observed in most of the recorded macrobenthic species, highlighting the adaptability of these species to low trophic availability in the ecosystem. Future biodiversity studies will need to explore the innermost and deepest areas to provide a more comprehensive inventory and understanding of the influence of environmental conditions on the structure and functioning of Young Sound benthic habitats.

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**Key words**

Benthic ecosystems • Macrofauna • Community structure • Spatial variability • Meltwater inputs • Arctic fjord
## 50 Introduction

To date, Arctic benthic biodiversity remains poorly studied although species colonizing the seafloor represent around 90 % of the total estimated species richness of Arctic invertebrates (Sirenko 2001; Gradinger et al. 2010). While Arctic benthic ecosystems have long been considered as areas of low species diversity (e.g. Knox and Lowry 1977), there is increasing evidence that this assumption has likely been biased by the scarcity of surveys conducted at high latitudes (Piepenburg 2005; Piepenburg et al. 2011). Recent inventories estimate the diversity of Arctic benthic species to be over 4600 species, a much higher number than previously estimated, while several thousand species are likely to remain to be discovered (Bluhm et al. 2011; Josefson et al. 2013). Although considerable progress has been made in Arctic biodiversity in recent decades, some geographic areas remain understudied such as East Greenland (Piepenburg et al. 2011).

Under climate change, Arctic benthic ecosystems are expected to undergo major modifications driven by changes in sea ice cover, salinity and temperature, acidification, or sedimentation (AMAP 2017). It is very likely that these changes will impact benthic biodiversity, especially in coastal areas, which are expected to be the most exposed to future environmental changes (Węsławski et al. 2011). The expansion of boreal species into high latitudes is also expected to affect benthic biodiversity by bringing new species into Arctic areas (Węsławski et al. 2011; Kotwicki et al. 2021; Cottier-Cook et al. 2023), with likely consequences for species interactions and ecosystem functioning. Indeed, the recent expansion of several engineer species with boreal affinities into the Arctic (e.g. mussel species from the *Mytilus* spp. complex or the kelp *Laminaria hyperborea*) has had implications for the structure of shallow benthic ecosystems by increasing habitat heterogeneity and complexity, facilitating the arrival of species new to these ecosystems (Berge et al. 2005; Krause-Jensen and Duarte 2014; Mathiesen et al. 2017; Filbee-Dexter et al. 2019; Kotwicki et al. 2021). Many questions remain unresolved regarding how endemic benthic species will cope with new abiotic conditions (increases in temperature or sedimentation, decreases in seawater salinity) and associated changes on biotic interactions (e.g. the arrival of new predators or competitors, Renaud et al. 2015). Assessing the vulnerability of Arctic benthic communities experiencing such environmental and ecological changes thus remains challenging and highlights the strong need for initial references states in benthic biodiversity in all Arctic ecoregions.
In this context, any increase in knowledge of the benthic biodiversity of poorly characterized Arctic ecoregions is crucial, especially in shallow coastal ecosystems. For example, the only studies conducted on the North-Eastern coasts of Greenland have focused on epifauna and/or megafauna shelf communities (e.g. Piepenburg and Schmid 1996; Brandt and Schnack 1999; Starmans et al. 1999; Fredriksen et al. 2020). To our knowledge, for such real *Terra Incognita* of Arctic ecoregions (Piepenburg et al. 2011), only Sejr et al. (2000) provided quantitative datasets on shallow macrozoobenthos assemblages in a high-Arctic fjord (Young Sound, NE Greenland). Few studies have also investigated trophic linkages in macrobenthic ecosystems from the Northeast Water Polynya providing only limited details on their biodiversity (Hobson et al. 1995; Ambrose and Renaud 1997; Piepenburg et al. 1997). Finally, although many older studies from the mid-20th century have been conducted on the shallow habitats (e.g. Ockelmann 1958), they have mostly focused on the occurrence of individual taxa than providing insights into the structure and diversity of macrobenthic communities.

The aim of the present study is to complement the inventory of benthic macrofaunal species carried out by Sejr et al. (2000) in Northeast Greenland (Young Sound, 74°N) with additional sampling sites. While Sejr et al. (2000) examined the macrobenthic communities in vertical zonation (from 20 to 85 m), this study prospects shallow benthic macrofaunal assemblages (≈ 20 m) distributed along a small inner/outer gradient located in the most marine part of the fjord. We resampled the shallowest Daneborg station from Sejr et al. (2000) and investigated three new stations, one towards the outer fjord (Kap Breusing) and two towards the inner fjord (Basalt Island, Pass Hytten). The description of the assemblages, coupled with those of Sejr et al. (2000), aims to provide a baseline for future studies investigating the temporal variability of Arctic shallow coastal soft-bottom communities and their response to ongoing climate change.

## 104 Materials and Methods

### 105 Study sites

Young Sound is a high Arctic fjord located in North-East Greenland (Fig. 1) of about 90 km long and 2-7 km wide (Rysgaard et al. 2003). A sill is located at its outer section (≈ 45 m depth, see Fig. 1) limiting seawater exchanges between the inner parts of the fjord and the shelf (Bendtsen et al. 2007) where average and maximum depths reach 100 and 360 m, respectively (Rysgaard et al. 2003). This fjord is characterized by extreme seasonal variations, thick sea ice (> 150 cm) and snow cover (20 – 100 cm) covering the fjord for 9 to 10 months per year (Glud
et al. 2007) and strongly limiting the annual primary production, estimated to be about 10 g C m⁻² yr⁻¹ (Rysgaard et al. 1999). During the summer, glacier and snow melt generate strong river flows ranging annually from 0.9 to 1.4 km³ (Bendtsen et al. 2014). Such freshwater inputs induce strong spatial salinity and temperature gradients in summer surface waters, with temperature decreasing from 9 to 2°C and salinity increasing from 8 to 30, from the inner to the outer part of the fjord, respectively (Bendtsen et al. 2007). In contrast, deeper waters (> 20 m) generally remain stable throughout the year (i.e. > 2° C) along the entire fjord length (Holding et al. 2019). Vertical variations in salinity induce a strong permanent haline stratification at 5 to 10 m depth, which limits pelagic primary production by reducing nutrient exchange between surface and subsurface waters (Holding et al. 2019; Sejr et al. 2022). On a decadal scale, the sea ice conditions in the fjord have changed with a gradual increase in the duration of the ice-free season from about 80 days per year (1950-2000) to more than 90 days per year but combined with a significant increase in the year-to-year variability since 2000. At the same time, freshwater runoff (mostly glacial meltwater) is estimated to have increased 6-7 fold since the 1960s (Sejr et al. 2022). Annual monitoring of main Young Sound environmental parameters (physico-chemical, pelagic productivity and community structure) has been made for three decades by the Greenland Ecosystem Monitoring – Marine Basis program, making Young Sound ideal for studying the effects and feedback of climate change in the high Arctic. However, the macrozoobenthic benthic communities are not part of the monitoring program since the study by Sejr et al. (2000), highlighting the crucial need to reacquire biodiversity data.

## Sampling and laboratory analyses

Sampling was conducted in August 2016 at four stations distributed along an inner/outer marine fjord gradient: Pass Hytten, Basalt Island, Daneborg and Kap Breusing (Fig. 1, Table 1). Macrofauna samples were collected by scuba divers for each replicate using a modified Hiscock and Hoare suction dredge (Eleftheriou and McIntyre 2005), fitted with a suction pipe directly connected to a nylon mesh sample bag (square mesh = 1 mm). Each replicate was collected over an area of 0.09 m² (except for one replicate at Kap Breusing, which was collected over 0.0625 m²) and then fixed directly in 10% buffered formalin. Sediment samples were also collected at both Pass Hytten and Kap Breusing using small sediment cores for grain size analysis. Due to logistical problems, we were unable to collect sediment samples at either Daneborg or Basalt Island. Once in the laboratory, the animals were sorted, transferred to 70% ethanol and then identified to the lowest taxonomic level. Sediment samples were analyzed by the private company “Eurofins – Analyses pour l’environnement” (Saverne, France) using laser
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methods: samples were sieved through a 2 mm square mesh and then analyzed using a Malvern
Mastersizer 2000 laser particle size analyzer to provide different size fractions ranging from 2
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Statistical analyses

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Spatial differences in benthic assemblage structure were visualized using Principal Component
Analysis (PCA) performed on Hellinger-transformed fauna abundances. This transformation
was selected to reduce the weight of rare species in the analysis (Legendre and Gallagher 2001).
The first twenty species explaining the most spatial variation in the ordination (i.e. accounting
for more than 60% of SIMPER dissimilarities) were plotted in a second graph to visualize which
species contributed to the benthic structure of each station. Spatial differences in community
structure were tested using one-way permutational multivariate analysis of variance
(PERMANOVA) performed on Bray-Curtis transformed fauna abundances. Homoscedasticity
was checked using a permutational analysis of multivariate dispersions (PERMDISP) test to
ensure that data dispersion did not influence the PERMANOVA result (Anderson et al. 2008;
Anderson and Walsh 2013). Species rarefaction curves were calculated for each replicate to
compare trends in species richness between stations. Species richness was compared among
replicates based on rarefaction curves by standardizing all data to the same abundance
 corresponsponding to the number of individuals in the replicate with the lowest abundance) to
remove any abundance bias on taxa richness (Gotelli and Colwell 2001). An additional
rarefaction curve was plotted to estimate the specific richness for the entire Young Sound
system and Hulbert's diversity index was calculated to estimate the expected number of species
within a random sample of 35 individuals (based on the lowest number of individuals observed
in a replicate). Jacknife1 Chao2 estimates were calculated and plotted as accumulation curves
to estimate the total species richness in case species rarefaction curves did not reach their
asymptotes (Colwell et al. 2004; Chao and Chiu 2016). Finally, we calculated the Pielou's
evenness index to take into account the diversity observed at each station along with the
associated species richness using the "vegan" R package (Oksanen et al. 2019). All other
diversity indices were calculated using EstimateS v9.1 software.

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173 **Results**

174 **Structure of benthic community**

175 Significant differences in benthic community structure were observed between sampling
176 stations (degrees of freedom for treatment and error [df] = 3 and 11, pseudo-F = 8.2529, p-perm
177 = 0.001). Pairwise analyses revealed that such differences were observed between all stations
178 (the smallest significant difference was observed between Basalt Island and Kap Breusing, df
179 = 1 and 4, pseudo-F = 7.4856, p-perm = 0.049). PCA analysis showed that more than half of
180 the spatial variability was explained by the first three principal components (PC1, PC2 and PC3
181 explained 24.36, 17.92 and 17.27 % of the variance, respectively). Low dispersion was
182 observed among the replicates of each station (Fig. 2a, c). Significant differences in Pielou's
183 evenness index were observed between stations (df = 3 and 14, pseudo-F = 36.4600, p-perm =
184 0.001). These differences were observed between all stations by pairwise PERMANOVA
185 analyses (the smallest significant difference was observed between Daneborg and Kap
186 Breusing, df = 1 and 4, pseudo-F = 16.2496, p-perm == 0.048), except between Pass Hytten
187 and Kap Breusing (df = 1 and 4, pseudo-F = 0.0386, p-perm = 1).

188 Benthic assemblages at Pass Hytten were strongly dominated by crustaceans (relative
189 abundance = 52.9 - 78.0%, Fig. 3a, b), mainly due to high densities of ostracods and the
190 amphipod *Metopa glacialis* (Fig. 2b). The community structure at Daneborg and Basalt Island
191 was more evenly balanced between taxa (Fig. 3a, b), although polychaetes were the most
192 dominant group (relative abundance = 32.6 - 58.3% at Daneborg and 44.9 - 55.9% at Basalt
193 Island). *Euchone analis*, *E. incolor* and *Laphania boecki* were the most abundant polychaete
194 species at Daneborg, while *Abyssoninoe* sp., *Laphania boecki* and *Nereimyra aphroditoides*
195 dominated the polychaete assemblage at Basalt Island (Fig. 2b, d). Finally, bivalves were the
196 dominant taxonomic group at Kap Breusing (relative abundance = 67.5 - 68.5%, Fig. 3a, b),
197 largely represented by high densities of the filter-feeding bivalves *Hiatella arctica* and
198 *Musculus discors* (> 50%, Fig. 2b, d).

199 Total abundance showed large variation among stations and replicates (Fig. 3b). The highest
200 abundances were observed in the second replicate from Kap Breusing (reaching 6044 ind. m⁻²,
201 Fig. 2b). In contrast, the first replicate from Kap Breusing showed a much lower total abundance
202 (1824 ind. m⁻²), which was in the same order of magnitude as the abundances observed at
203 Daneborg (from 933 to 1733 ind. m⁻²) and Pass Hytten (from 1467 to 2667 ind. m⁻², Fig. 2b).
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Finally, the lowest total abundances were observed at Basalt Island (from 389 to 1611 ind. m⁻², Fig. 2b).

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## Abiotic and biotic description of benthic habitats

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### Pass Hytten

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The sediment texture is dominated by fine silt particles (55% of the total size fraction for particles < 63 µm) mixed with fine sands (25%) and gravels (20%, Fig. 1 in Online Resource 1). Significant bioturbation activity probably occurs due to high abundances of epifauna (e.g. *Ophiocten sericeum*, Fig. 4a, Table 2) and burrowing shrimps (e.g. *Sclerocrangon boreas*, L. Chauvaud pers. obs.). The associated macrozoobenthic assemblage shows a low species evenness with ten taxa representing 83.5% of the total abundance (Table 2), including crustaceans such as ostracods, the amphipod *Metopa glacialis* and the cumacean *Diastylis scorpioides* (59% of the total abundance). The strictly benthic species (epifauna and endofauna) were dominated by both tube-dwelling (*Euchone incolor* [see high abundances in Fig. 3a], *Lyssipe labiata*, *Maldane sarsi* and *Owenia borealis*) and errant polychaetes (*Abyssoninoe* sp. and *Leitoscoloplos mammosus*). Bivalves *Astarte moerchi*, *Hiatella arctica*, *Mya truncata* and *Musculus discors* also occur but in much lower proportions (< 15% of the total abundance).

### Basalt Island

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Here, the sediment is a mixture of stone, sand and small gravel (2-5 mm) associated with detrital organic matter (mainly macroalgae and shell debris) accumulated on the seafloor (Fig. 4b). However, we were unable to sample the sediment at this station due to the dominance of stones. The steep slope of the seafloor (slope gradient ≈ 80 – 100 %, see Fig. 4b) probably makes the bottom unstable due to the downward export of mineral material towards the deep fjord basins. The species assemblage at Basalt Island shows greater species evenness than Pass Hytten and Kap Breusing, with the ten most dominant species accounting for only 51.3% of total abundance (Table 2). Polychaetes dominate the species assemblage with *Abyssoninoe* sp., *Clymenura* sp., *Laphania boecki*, *Nereimyra aphroditoides* and *Pholoe* sp. representing 26.4% of the total abundance. Several bivalves such as *A. moerchi*, *H. arctica* or *M. truncata* were also found at the site but in low abundances, as well as the brittle star *Ophiocten sericeum* (Table 2, Table S1 in Online Resource 1). Among crustaceans, ostracods show a high abundance (5.9%, Table 2).

### Daneborg

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Based on underwater pictures and previous data on particle size distribution (Sejr et al. 2000), the seabed was characterized by a mixture of fine and very fine sand (particles [63 - 125 µm] =
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24.6 % and particles > 125 µm = 44.2 %). The species evenness of the species assemblage was close to that observed at Basalt Island (Table 2). Daneborg is mainly dominated by two taxa, bivalves and in particular the species *Astarte moerchi* (18.6 %) and crustaceans (ostracods and *D. scorpioides* representing 11.8 % and 3.1 % of the total abundance, respectively). Polychaetes complete the assemblage, including *Euchone incolor*, *Laphania boecki*, *Euchone analis*, *Chone* sp. and *Clymenura* sp., which all account for 23.6% of the total abundance.

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Kap Breusing

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The grain size distribution of Kap Breusing was variable between replicates, but overall it was a poorly sorted sandy sediment (the 63-2000 µm grain size range varied from 53 to 80 %, Fig. S1 in Online Resource 1). Heterogeneous medium/coarse sand (38 to 55 % of the particles between 250 and 2000 µm) was found in two of the three replicates, the other was largely composed of fine sand (61 % of particles between 63 and 250 µm).

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The species assemblage here was associated with a rock wall close to the location where the sediment samples were collected and included Sertulariidae hydrozoans and *Musculus discors* bivalves (L. Chauvaud, pers. obs., see background of Fig. 4d). Both species form a complex three-dimensional structure hosting a highly diversified assemblage including the gastropod *Alvania scrobiculata* and the bivalves *A. moerchi*, *H. arctica*, *M. discors* and *M. truncata*, representing more than 68% of the total abundance (Table 2). Four vagile polychaete species were also found as *Harmothoe* sp., *Nereimyra aphroditoides*, *Nereis zonata* and *Syllis* sp. (11.3 % of total abundance) and the sedentary terebellid *Polycirrus medusa* (2.8 %; Table 2).

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## Biodiversity estimates of benthic habitats

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Based on a total area of 1.32 m² sampled by 15 suction dredge replicates, we collected a total of 2322 individuals belonging to 166 species (Table S1 in Online Resource 1). The polychaete phylum was by far the most diverse (67 species), followed by mollusks (33 species) and crustaceans (31 species). Echinoderms, nemerteans, sipunculans, pycnogonids, tunicates, nematodes, brachiopods and platyhelminths were also found but always displayed with much lower species richness. Macroalgae randomly collected in our samples were also identified, and the species list is included in the supplementary material as complementary observations (Table S2 in Online Resource 1).

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Species accumulation curves did not reach their asymptotes for all stations (Fig 5). The initial slope of the species accumulation curves was highly variable between stations, but more consistent between intra-site replicates. Based on the lowest number of individuals (i.e. 35 in the 5th Basalt Island replicate), Hulbert's expected species richness within a random sample of

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35 individuals (ES35) displayed the lowest levels in Pass Hytten and Kap Breusing (i.e. range ES35 = 9 – 13 and 12 – 13 for Pass Hytten and Kap Breusing, respectively). Expected species richness showed intermediate values in Daneborg (range ES35 = 15 – 21) and the highest levels in Basalt Island (range ES35 = 19 – 22). Based on the total number of species per replicate (Stot), species richness was also lower at Pass Hytten (range Stot = 17 – 31) than at Basalt Island (range Stot = 19 – 43) and Daneborg (range Stot = 32 – 47), while Kap Breusing had the highest intra-station variability (range Stot = 27 – 59). A rarefaction curve based on the total set of fauna samples (i.e. all replicates from the four sampled stations combined) also does not reach an asymptote either, despite the much higher number of individuals (i.e. > 2000).

The rarefaction curves of Chao2 and Jackknife1 estimates slightly differ from the species accumulation curves (Fig. 6a, b). Based on the lowest number of replicates (i.e. 2 sampled stations at Kap Breusing), biodiversity estimates were lowest at Pass Hytten (Chao2 = 48, Jackknife1 = 51), intermediate at Basalt Island (Chao2 = 62, Jackknife1 = 64) and Daneborg (Chao2 = 77, Jackknife1 = 78), and highest at Kap Breusing (Chao2 = 95, Jackknife1 = 91). Based on the entire dataset, Chao2 and Jackknife1 estimates predicted a total species richness of 204 and 221 species, respectively.

## Discussion

### Benthic species richness of the study area: historical and recent data comparison

The present study complements the previous work of Sejr et al. (2000) conducted twenty years ago in Young Sound, which described gradual, spatially limited changes in species assemblages along a depth gradient (from 20 to 85 m) in the vicinity of Daneborg station (Fig. 1). Our study conducted along a small inner/outer fjord gradient in the most marine part of Young Sound shows little spatial variation in shallow (above 20 m depth) benthic community structure. This pattern suggests that our four sampling stations cover a relatively continuous and uniform habitat. The sampled habitat is mostly dominated by large tubicolous polychaetes (e.g. Maldanidae, *Euchone*) and some specific motile polychaetes (*Leitoscoloplos*, *Lumbreneris*), and has a high abundance of suspension-feeding bivalves (e.g. *Astarte*, *Bathyarca*, *Hiatella*). Turbidity and meltwater inputs are generally factors that control community structure in Arctic fjords, decreasing the presence of filter feeders towards the inner areas of fjords exposed to glacial melt (Włodarska-Kowalczuk and Pearson 2004; Sejr et al. 2010; Włodarska-Kowalczuk et al. 2012; Udalov et al. 2021). However, we doubt that turbidity and meltwater inputs account for the spatial variations observed between our four stations, as weak environmental forcing is observed along the small inner/outer fjord gradient studied in our survey. In fact, although
turbidity reaches more than 50 NTU in the innermost parts of Young Sound, it only varies from 302 2-3 to less than 1 NTU between Pass Hytten and Kap Breusing (Meire et al. 2017). It is therefore 303 more likely that the observed spatial variability in community structure reflects small-scale 304 habitat variation (bottom varying abundance in bare rock, fine sand, mixed sand and gravel or 305 mud) rather than large-scale environmental variation (i.e. differences in exposure to meltwater 306 inputs). 307

The present study provides a complementary census of 166 benthic species, including 308 numerically dominant polychaetes (67 species), crustaceans (46 species) and mollusks (33 309 species). It complements the previous work by Sejr et al. (2000) which listed a total of 100 310 species despite a higher sampling effort (total sampled surface = 2.24 m² vs 1.3225 m² here). 311 With only 41 species in common between both studies, the total number of benthic invertebrate 312 species recorded from the Young Sound now reaches a total of 225. The relatively low number 313 of taxa shared between the two inventories mainly reflects the different sampling strategies as 314 Sejr et al. (2000) targeted species assemblages from increasing depths while our sampling 315 focused on a limited spatial fjord gradient that covers contrasting shallow habitats (i.e. silt, 316 sand/gravel, rocky wall) and their associated species assemblages. 317

It should also be noted that identification bias cannot be excluded as a single species may be 318 recorded under two different names over time, as different identification experts were involved 319 and taxonomical descriptions have been produced since 2000. As an example, *Scoloplos* 320 *armiger* (only in Sejr et al. 2000) and *Leitoscolopos mammosus* (only here) have been reported 321 to taxonomic confusion (Mackie 1987; Renaud et al. 2007). Further census efforts will include 322 harmonization of the species list with the involvement of benthic taxonomy experts. It could be 323 assumed that the relatively low number of species common to this inventory and the study by 324 Sejr et al. (2000) is due to long-term variability in benthic community structure. However, this 325 seems unlikely as previous studies conducted in Arctic silled-fjord show a high stability of 326 benthic community structure over several decades (Renaud et al. 2007), in contrast to open 327 fjords (Beuchel et al. 2006; Kortsch et al. 2012). 328

As indicated by the slopes of the species accumulation curves, the inventory of benthic 329 biodiversity in this fjord is far from being complete, with many rare species likely yet to be 330 recorded at all study sites. The expected number of species per 35 individuals (ES35) varies 331 between 9 and 22 species, underlining the high biodiversity but also the heterogeneity across 332 stations and replicates. Based on biodiversity estimates, total species richness of the outer fjord 333
334 shallow sites should reach around 204-221 species, much higher than previous estimates based
335 on Sejr et al. (2000) and this should be much higher as only a very limited part of the shallow
336 Young Sound has been visited and a wide variety of habitats remains unexplored. Inventory
337 studies on shallow and deep areas of both outer and inner fjord usually find much higher species
338 diversity than in the present work. For example, Kędra et al. (2010) recorded more than 300
339 taxa after extensive multi-year sampling of all soft-bottom habitats in Hornsund (SW Svalbard,
340 from 30 m to 250 m), and Voronkov et al. (2013) found 403 benthic taxa in shallow hard-bottom
341 communities from Kongsfjorden (NW Svalbard). We thus think that the actual benthic species
342 inventory of the Young Sound is far from complete, as it is limited to the only most marine
343 section.

344 Ecological characteristics and insights about the functioning of the benthic fauna

345 *Ecological characteristics of benthic assemblages*

346 The current inventory identifies four major benthic assemblages, all belonging to the Young
347 Sound outer fjord benthic community: 1) the rocky outer fjord assemblage (Kap Breusing), 2)
348 the sandy outer fjord assemblage (Daneborg), 3) the sand-gravelly outer fjord assemblage
349 (Basalt Island) and 4) the silty outer fjord assemblage (Pass Hytten).

350 The macrobenthic assemblage collected at Kap Breusing was composed of a unique and poorly
351 described species assemblage dominated by two engineer species, the bivalve *Musculus discors*
352 and the sertulariid colonial hydroids. Several studies have highlighted the ability of some
353 bivalve species to secrete byssus threads to construct nests that host a high diversity of other
354 benthic invertebrate species (e.g. *Arcuatula senhousia*, *Limaria hians*; Morton 1974; Hall-
355 Spencer and Moore 2000). Byssus threads produced by these species transform the physical
356 habitat into a complex three-dimensional structure that is then colonized by hydroids (Merrill
357 and Turner 1963). To our knowledge, only one study has reported this ability for *M. discors*
358 (Merrill and Turner 1963). The high biodiversity observed at Kap Breusing (where the highest
359 number of species was observed within a single replicate) reflects the structuring effect of the
360 *M. discors* / Sertulariidae assemblage on the community structure. The high abundance and
361 diversity of motile polychaetes in this assemblage, especially for Nereididae, Polynoidae or
362 Syllidae, is similar to assemblages observed in complex three-dimensional habitats such as
363 maerl beds, kelp forests or artificial structures (Grall et al. 2006; Yakovis et al. 2007; Pabis and
364 Sicinski 2010). The *M. discors* / Sertulariidae assemblage was also dominated by large
365 suspension-feeding bivalves (*Hiatella arctica*, *Musculus discors* and *Mya truncata*), which is
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more in line with common species assemblages observed on seafloors protected from sediment
disturbance caused either by freshwater inputs or by burrowing species (Włodarska-Kowalczuk
2007).

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The outer fjord sandy assemblage of Daneborg was dominated by the bivalve *Astarte moerchi*, ostracods and polychaetes of the genus *Euchone*. The dominance of *A. moerchi* among the bivalves collected at Daneborg is similar to that observed by Sejr et al. (2000) at the same station but community structure differs with our data: several abundant polychaete species found in 2016 (e.g. *Clymenura* sp., *Euchone* spp., *Laphania boecki*) were not observed by Sejr et al. (2000) while other species abundant in 1995 (e.g. *Dipolydora quadrilobate* and *Lumbriclymene minor*) were not collected in 2016. Such long-term differences could be explained either by long-term changes in the benthic assemblages but also to our weak sampling effort that is submitted to small scale habitat heterogeneity.

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The Basalt Island sand-gravel outer fjord assemblage is dominated by an association of motile polychaetes (*Abyssoninoe* sp., *Clymenura* sp., *L. boecki*, *Nereimyra aphroditoides*, *Pholoe* sp.), ostracods and the bivalve *A. moerchi*. Although the associated community structure differs with that of Daneborg, both display several common dominant species (e.g. *A. morchi*, *Clymenura* sp., *L. boecki*) indicating common ecological characteristics potentially related to their vicinity in the fjord and similar environmental constraints.

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Finally, the silty outer fjord assemblage collected at Pass Hytten is dominated by ostracods, the *Metopa glacialis* amphipod as well as tube-dwelling polychaete species (e.g. *Maldane sarsi*, *Owenia borealis*, *Euchone* sp.) and crustaceans. Surprisingly, several species described in the literature as typical of either outer or inner fjord assemblages are found in association in Pass Hytten. For instance, the sub-surface deposit feeder *M. sarsi* is the most dominant polychaete although it is reported to be typical of outer fjord assemblages (Gulliksen et al. 1985; Renaud et al. 2007; Kędra et al. 2013), whereas it is absent from inner fjord areas (Włodarska-Kowalczuk et al. 2012). Surface deposit-feeding thyasirids and nuculanids are also present, albeit in moderate abundance, at Pass Hytten, although they are generally representative of benthic assemblages from inner fjord areas (Włodarska-Kowalczuk and Pearson 2004). The presence of *Euchone* sp. or *Leitoscoloplos mammosus* polychaetes in Pass Hytten is also consistent with previous observations made in shallow and deep areas exposed to high sedimentation rates (Sejr et al. 2010; Kędra et al. 2013; McGovern et al. 2020). Therefore, the coexistence of several species typical of both outer and middle/inner fjord assemblages at Pass Hytten is also supported by the data.

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Hytten suggests that although this site is more similar to outer fjord habitats, the presence of a handful of species adapted to high sediment loads would indicate that this station is approaching the transition zone between the outer and inner parts of the fjord. This could be explained by the more interior location of Pass Hytten compared to the other three stations sampled, as well as its location closer to the Zackenberg River delta. We hypothesize that future sampling, either in the innermost part of the fjord or closer to the Zackenberg delta, will identify new species assemblages typical of benthic habitats from areas exposed to glacial and freshwater inputs.

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*New insights about the functioning of the shallow benthic outer fjord community*

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The new data from our study provide a better understanding of the importance of trophic adaptations for benthic community functioning in outer fjord habitats. A complete analysis of the trophic structure of benthic assemblages has already been conducted at Pass Hytten and Kap Breusing by Bridier et al. (2021). It appears that several dominant species in our study are known to have high trophic plasticity (i.e. feeding on several carbon sources, De Cesare et al. 2017; Bridier et al. 2021). The bivalves *Astarte moerchi*, *Astarte elliptica*, *Hiatella arctica*, and *Musculus discors* in Young Sound appear to feed on a range of carbon sources such as phytoplankton, benthic organic matter (i.e. macroalgae and/or microphytobenthos) or sedimentary organic matter (detritus, Bridier et al. 2021). For some species (e.g. the astartidae *A. moerchi* and *A. elliptica*), the proportion of alternative organic matter resources can even reach almost 50% of their diet (Bridier et al. 2021). In addition, other species abundant in Young Sound are known to be omnivores (i.e. feeding on several trophic levels, McMeans et al. 2015; Bridier et al. 2021). This is particularly true for the brittle star *Ophiocten sericeum*, the amphipod *Metopa glacialis* and the polychaete *Nereis zonata*, which were observed in high abundance at all stations. Although the brittle star *O. sericeum* is generally considered a surface feeder, it falls between the primary and the secondary consumer levels in Young Sound (Bridier et al. 2021). Conversely, the polychaete *N. zonata* and the amphipod *M. glacialis* exhibit trophic levels below those of the strict predators with which they are generally associated (Bridier et al. 2021). These variations in trophic position show that these species are capable of feeding at multiple trophic levels, feeding on sources of primary organic matter when these are available in the ecosystem, or feeding at higher trophic levels when the availability of primary production is low (McMeans et al. 2015; Bridier et al. 2021). All these trophic adaptations likely reflect the low pelagic productivity of Young Sound, which ranks among the least productive coastal ecosystems in the world, with pelagic primary production estimated at 10 g C m⁻² yr⁻¹ (Rysgaard et al. 1999; Cloern et al. 2014). Trophic plasticity might therefore allow species to adapt to this
low pelagic primary production by optimizing carbon flows through food webs through the exploitation of all carbon sources available in the ecosystem (e.g. microphytobenthos, macroalgae, detritus, Mincks et al. 2008; Renaud et al. 2015). Omnivory may also help benthic species to adapt to low pelagic primary production by reusing carbon that has already passed through the food web a second time, thus participating in the recycling of carbon circulating in the community.

The present study complements previous work by Bridier et al. (2021) on the functioning of benthic communities in the shallow habitats of Young Sound. Although Bridier et al. (2021) highlighted the existence of trophic adaptations for several benthic species in Young Sound, the paucity of information on benthic community structure prevents drawing conclusions on the functioning of benthic communities in outer fjord habitats. The new data presented here show that the observations on community trophic adaptations involve species that are numerically dominant in the inventoried benthic habitats (i.e. the rocky, sandy and silty outer fjord assemblages). For example, the species *H. arctica*, *M. discors* (characterized by high trophic plasticity) and *N. zonata* (characterized by high levels of omnivory) alone account for 66.5% of the total abundance at Kap Breusing. It could be argued that biomass data would have been more appropriate than abundance data to discuss the role of these latter species in community carbon fluxes. However, considering that all species mentioned as omnivorous or trophically plastic are larger than the rest of the species identified in this study, the biomass dominance of these individuals is likely greater than their numerical dominance, suggesting then an even greater role for community carbon fluxes. Trophic adaptations thus play a predominant role in the functioning of the outer fjord benthic communities, which feed only partially on fresh organic matter from pelagic primary production. These results also highlight the crucial role of benthic primary producers in the functioning of shallow Arctic coastal ecosystems, whose importance is often underestimated, although they represent a significant carbon source (Attard et al. 2016; Gaillard et al. 2017; Ørberg et al. 2022). With climate change, increased meltwater inputs will have multiple consequences for Young Sound's pelagic environments, including impacts on pelagic primary production, organic matter quality and organic matter transfers to zooplankton (Meire et al. 2017; Middelbo et al. 2018; Bridier et al. 2019). The existence of trophic adaptations in several species that dominate the benthic communities of the outer fjord (and therefore potentially represent major carbon transfer pathways) could thus be a crucial advantage for their resilience in the face of upcoming environmental changes. In the future, it would be important to investigate the community and
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trophic structures of the inner fjord to observe how the dominance of these trophic adaptations evolves in habitats exposed to stronger meltwater inputs and higher trophic constraints. In addition, it would also be interesting to describe the structure of benthic communities and food webs in the deeper basins of the fjord (up to 350 m), which do not benefit from local benthic primary production.

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## Conclusion and further directions of research

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The species list obtained in this study is a substantial addition to the inventory carried out two decades ago, adding 66 new species to the 100 already listed by Sejr et al. (2000). The sampling of three new stations (Pass Hytten, Basalt Island, Kap Breusing) in addition to the station previously described by Sejr et al. (2000) (i.e. Daneborg) also provides new insights into the spatial variability of benthic communities in this fjord. Although the community structure differs significantly between the four stations, these differences remain small overall, suggesting that these stations all belong to the same habitat type. Comparison of the community structure with that of the literature suggests that the four stations are characteristic of outer fjord assemblages.

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Young Sound is a unique location in the Arctic where annual monitoring has been conducted for over 20 years by the Greenland Ecosystem Monitoring - MarineBasis Program. This fjord is therefore an ideal candidate for future biodiversity inventories in northeast Greenland which is one of the Arctic regions with the least studied benthic communities (Piepenburg et al. 2011). Additional sampling will undoubtedly be needed to improve our knowledge of the structure, dynamics and functioning of the Young Sound benthic habitats and associated biodiversity. This sampling should be prioritized in the deeper silty basins (up to 350 m), but also in the inner (i.e. Tyrolerfjord) and intermediate sections of the fjord, which are more exposed to strong freshwater inputs, turbidity and sedimentation. On the opposite, the fjord mouth should also be explored to sample various habitats made up of coarse sands, gravels or potentially biogenic habitats. According to the literature, the innermost parts of the fjord should be dominated by opportunistic species (e.g. the cirratulid polychaete *Chaetozone* spp.) and mollusks feeding on surface deposits such as small thyasirid and nuculanid bivalves (e.g. Włodarska-Kowalczuk and Pearson 2004; Sejr et al. 2010; Włodarska-Kowalczuk et al. 2012), which seem to be underrepresented in the samples analyzed in this study. Finally, the more oceanic part of the fjord should contain a wide variety of benthic habitats characterized by a high and original
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biodiversity, including biogenic habitats (e.g. maerl/rhodolith or horse mussel beds could be
typical in such an environment).

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These data will be crucial for future predictions on the evolution of benthic communities in
response to future global changes, and in particular increased freshwater inputs to coastal areas
in response to the accelerated melting of the Greenland Ice Sheet (Mouginot et al. 2019; Höning
et al. 2023). Although the structure of benthic communities from sill fjords is generally
considered to be stable on multi-decadal scales (Renaud et al. 2007), the long-term dynamics
of benthic communities in Artic fjords are still poorly understood. To date, few long-term
monitoring studies have been carried out in the Arctic, and to our knowledge none in East
Greenland. It would therefore be important to carry out such monitoring to ensure community
stability over longer time scales, especially when warmer water masses of Atlantic origin are
increasing along the Northeast Greenland Shelf (Gjelstrup et al. 2022) and could drive an
expansion of boreal species into the region. Complementary sampling methods, including
scientific SCUBA diving, have been used in other Arctic regions (e.g., Svalbard) to study
shallow benthic communities (i.e., < 30 m, e.g., Jørgensen and Gulliksen 2001). For example,
image analysis based on photographs taken by SCUBA divers has been used to study small-
scale spatial variability in benthic communities (Jørgensen and Gulliksen 2001) or long-term
successional dynamics following episodes of disturbance or climate change (Beuchel et al.
2006; Beuchel and Gulliksen 2008; Al-Habahbeh et al. 2020). Applying these methods to future
studies in Young Sound could be an interesting way to obtain complementary data on benthic
communities and would also allow comparative studies with Svalbard fjords, which have been
studied for several decades.

517
518 Author contributions

519 FO, LC, MKS conducted the field sampling campaign. GB, LP, JJ, TB, MLD and JG conducted
520 species identifications. GB carried out the statistical analyses, interpreted the results and wrote
521 the original draft of the manuscript. FO, LP, JJ, LC, MKS, TB, MLD, and JG helped to interpret
522 the results and write the manuscript. FO, LC, MKS, and JG obtained the necessary funding for
523 the study. FO, LC, and JG developed the sampling design. All authors read and approved the
524 manuscript.

525 Acknowledgements

526 We are grateful to Erwan Amice for his valuable help on the field and for sharing his photos
527 for Fig. 4. We are grateful to Egon Randa Frandsen, Mie Sichlau Winding and Carl Isaksen for
528 their contribution in the field, collecting samples for sediment analyses. A big thank to Gabin
529 Droual, Vincent Le Garrec, Carolin Uhlir, Anne-Helene Tandberg and Natalia Shunatova for
530 their help on species identification. Friendly thanks to Adeline Tauran for calculation of Chao2
531 and Jackknife1 estimates. This work was conducted as a part of the PhD of Guillaume Bridier
532 co-founded by the Université de Bretagne Occidentale/LIA BeBEST and the “Allocation de
533 Recherche Doctorale” of the Brittany Regional Council. The authors are grateful to Christine
534 Michel and Paul Renaud as well as the two anonymous reviewers and the editor Dr. Alexey
535 Sukhotin for their comments which improved this manuscript.

536 Statements and Declarations

537 **Competing Interests:** The authors declare that they have no known competing financial
538 interests or personal relationships that could have appeared to influence the work reported in
539 this paper.

540 **Data availability:** All data supporting the results and analyses in this article are available in
541 the tables included in Online Resource 1.

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784
<figure><img src="image_2.png" /></figure>
<figure><img src="image_3.png" /></figure>

791

792 **Figure 2** Principal component analyses based on Hellinger-transformed fauna abundances.
793 Upper plots (a, b) show the first two principal components while lower plots show the first and
794 third principal components. Left plots (a, c) represent the position of each replicate while right
795 plots (b, d) represent the position of the first twenty species that explain at least 60 % of the
796 spatial variation

797
<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /><figcaption>799
800 **Figure 3** Relative abundance (%, a) and total abundance (ind. m⁻², b) of major taxonomic groups
801 from Pass Hytten (from PH 1 to PH 3), Basalt Island (from BI 1 to BI 5), Daneborg (from DA
802 1 to DA 2) and Kap Breusing (KB 1 & KB 2) stations</figcaption></figure>
<figure><img src="image_6.png" /></figure>

805

806 **Figure 4** Submarine landscapes of Pass Hytten (a, depth = 18 m), Basalt Island (b, depth = 21.5 m), Daneborg (c, depth = 20 m) and Kap Breusing stations (d, depth = 20 m). Photo credits:

807

808 Erwan Amice

809
<figure><img src="image_7.png" /></figure>

811

812 **Figure 5** Accumulation curves for each replicate from Pass Hytten, Basalt Island, Daneborg
813 and Kap Breusing stations and the entire Young Sound site (combining 15 replicates). The
814 vertical line represents the number of individuals selected for comparisons between replicates
815 (35 individuals)

816
<figure><img src="image_8.png" /></figure>

818

819 **Figure 6** Chao2 (a) and Jackknife1 (b) accumulation curves calculated for Pass Hytten, Basalt Island, Daneborg, Kap Breusing and the four stations combined.
820

821
822 Tables

823 **Table 1** Geographic coordinates, depth, total area sampled, and material collected (with number
824 of replicates in brackets) for each station

<table><thead><tr><th>Station</th><th>Latitude</th><th>Longitude</th><th>Depth (m)</th><th>Total sampled area (m²)</th><th>Collected material</th></tr></thead><tbody><tr><td>Pass Hytten</td><td>N 74.41'</td><td>W 20.33'</td><td>18.0</td><td>0.2700</td><td>Macrofauna (n = 3) and sediment (n = 1)</td></tr><tr><td>Basalt Island</td><td>N 74.33'</td><td>W 20.36'</td><td>21.5</td><td>0.4500</td><td>Macrofauna (n = 5)</td></tr><tr><td>Daneborg</td><td>N 74.31'</td><td>W 20.24'</td><td>20.0</td><td>0.4500</td><td>Macrofauna (n = 5)</td></tr><tr><td>Kap Breusing</td><td>N 74.21'</td><td>W 20.11'</td><td>20.0</td><td>0.1525</td><td>Macrofauna (n = 2) and sediment (n = 3)</td></tr></tbody></table>

825
<table><caption>**Table 2** List of the ten most abundant taxa for each station, with their relative abundance (%), their cumulative relative abundance (% Cum.), their abundance (Abund., number of individuals per square meter [ind. m⁻²]) and the Pielou index (mean ± standard error of the mean) of the corresponding station (calculated at the scale of the whole community)</caption><thead><tr><th>Species</th><th>Phylum</th><th>Abund.</th><th>%</th><th>Cum. %</th></tr></thead><tbody><tr><td colspan="5" style="text-align: center; font-weight: bold;">Pass Hytten</td></tr><tr><td colspan="5" style="text-align: center;">[Pielou index = 0.622 ± 0.027]</td></tr><tr><td>Ostracoda Latreille, 1802</td><td>Arthropoda</td><td>996.3</td><td>47.2</td><td>47.2</td></tr><tr><td>Metopa glacialis (Krøyer, 1842)</td><td>Arthropoda</td><td>185.2</td><td>8.8</td><td>56.0</td></tr><tr><td>Maldane sarsi Malmgren, 1865</td><td>Polychaeta</td><td>166.7</td><td>7.9</td><td>63.9</td></tr><tr><td>Owenia borealis Koh, Bhaud & Jirkov, 2003</td><td>Polychaeta</td><td>114.8</td><td>5.4</td><td>69.3</td></tr><tr><td>Leitoscoloplos mammosus Mackie, 1987</td><td>Polychaeta</td><td>63.0</td><td>3.0</td><td>72.3</td></tr><tr><td>Diastylis scorpioides (Lepechin, 1780)</td><td>Arthropoda</td><td>63.0</td><td>3.0</td><td>75.3</td></tr><tr><td>Abyssoninoe sp. Orensanz, 1990</td><td>Polychaeta</td><td>48.1</td><td>2.3</td><td>77.5</td></tr><tr><td>Lysippe labiata Malmgren, 1866</td><td>Polychaeta</td><td>44.4</td><td>2.1</td><td>79.6</td></tr><tr><td>Euchone incolor Hartman, 1965</td><td>Polychaeta</td><td>40.7</td><td>1.9</td><td>81.6</td></tr><tr><td>Ophiocten sericeum (Forbes, 1852)</td><td>Polychaeta</td><td>37.0</td><td>1.8</td><td>83.3</td></tr><tr><td colspan="5" style="text-align: center; font-weight: bold;">Basalt Island</td></tr><tr><td colspan="5" style="text-align: center;">[Pielou index = 0.916 ± 0.004]</td></tr><tr><td>Laphania boecki Malmgren, 1866</td><td>Polychaeta</td><td>64.4</td><td>6.6</td><td>6.6</td></tr><tr><td>Ostracoda Latreille, 1802</td><td>Arthropoda</td><td>57.8</td><td>5.9</td><td>12.5</td></tr><tr><td>Abyssoninoe sp. Orensanz, 1990</td><td>Polychaeta</td><td>55.6</td><td>5.7</td><td>18.2</td></tr><tr><td>Nereimyra aphroditoides (O. Fabricius, 1780)</td><td>Polychaeta</td><td>55.6</td><td>5.7</td><td>23.9</td></tr><tr><td>Nematoda</td><td>Nematoda</td><td>55.6</td><td>5.7</td><td>29.6</td></tr><tr><td>Ophiocten sericeum (Forbes, 1852)</td><td>Echinodermata</td><td>51.1</td><td>5.2</td><td>34.9</td></tr><tr><td>Astarte moerchi Hopner Petersen, 2001</td><td>Mollusca</td><td>46.7</td><td>4.8</td><td>39.6</td></tr><tr><td>Clymenura sp. Verrill, 1900</td><td>Polychaeta</td><td>42.2</td><td>4.3</td><td>44.0</td></tr><tr><td>Harmothoe cf. imbricata (Linnaeus, 1767)</td><td>Polychaeta</td><td>42.2</td><td>4.3</td><td>48.3</td></tr><tr><td>Pholoe assimilis Örsted, 1845</td><td>Polychaeta</td><td>40.0</td><td>4.1</td><td>52.4</td></tr><tr><td colspan="5" style="text-align: center; font-weight: bold;">Daneborg</td></tr><tr><td colspan="5" style="text-align: center;">[Pielou index = 0.834 ± 0.022]</td></tr><tr><td>Astarte moerchi Hopner Petersen, 2001</td><td>Mollusca</td><td>271.1</td><td>18.6</td><td>18.6</td></tr><tr><td>Ostracoda Latreille, 1802</td><td>Arthropoda</td><td>171.1</td><td>11.8</td><td>30.4</td></tr><tr><td>Euchone incolor Hartman, 1965</td><td>Polychaeta</td><td>91.1</td><td>6.3</td><td>36.6</td></tr><tr><td>Laphania boecki Malmgren, 1866</td><td>Polychaeta</td><td>75.6</td><td>5.2</td><td>41.8</td></tr><tr><td>Euchone analis (Krøyer, 1856)</td><td>Polychaeta</td><td>62.2</td><td>4.3</td><td>46.1</td></tr><tr><td>Chone cf. paucibranchiata (Krøyer, 1856)</td><td>Polychaeta</td><td>57.8</td><td>4.0</td><td>50.1</td></tr><tr><td>Clymenura sp. Verrill, 1900</td><td>Polychaeta</td><td>57.8</td><td>4.0</td><td>54.0</td></tr><tr><td>Diastylis scorpioides (Lepechin, 1780)</td><td>Arthropoda</td><td>51.1</td><td>3.5</td><td>57.6</td></tr><tr><td>Chaetozone sp. 1 Malmgren, 1867</td><td>Polychaeta</td><td>31.1</td><td>2.1</td><td>59.7</td></tr><tr><td>Harmothoe cf. imbricata (Linnaeus, 1767)</td><td>Polychaeta</td><td>24.4</td><td>1.7</td><td>61.4</td></tr><tr><td colspan="5" style="text-align: center; font-weight: bold;">Kap Breusing</td></tr><tr><td colspan="5" style="text-align: center;">[Pielou index = 0.634 ± 0.062]</td></tr><tr><td>Musculus discors (Linnaeus, 1767)</td><td>Mollusca</td><td>1875.4</td><td>43.7</td><td>43.7</td></tr><tr><td>Hiatella arctica (Linnaeus, 1767)</td><td>Mollusca</td><td>800.0</td><td>18.7</td><td>62.4</td></tr><tr><td>Harmothoe cf. imbricata (Linnaeus, 1767)</td><td>Polychaeta</td><td>242.6</td><td>5.7</td><td>68.0</td></tr><tr><td>Nereis zonata Malmgren, 1867</td><td>Polychaeta</td><td>177.0</td><td>4.1</td><td>72.2</td></tr><tr><td>Polycirrus medusa Grube, 1850</td><td>Polychaeta</td><td>85.2</td><td>2.0</td><td>74.2</td></tr><tr><td>Alvania scrobiculata (Møller, 1842)</td><td>Mollusca</td><td>78.7</td><td>1.8</td><td>76.0</td></tr><tr><td>Mya truncata Linnaeus, 1758</td><td>Polychaeta</td><td>65.6</td><td>1.5</td><td>77.5</td></tr><tr><td>Polycirrus latidens Eliason, 1962</td><td>Polychaeta</td><td>52.5</td><td>1.2</td><td>78.7</td></tr><tr><td>Nereimyra aphroditoides (O. Fabricius, 1780)</td><td>Polychaeta</td><td>45.9</td><td>1.1</td><td>79.8</td></tr><tr><td>Apherusa sarsi Shoemaker, 1930</td><td>Arthropoda</td><td>45.9</td><td>1.1</td><td>80.9</td></tr></tbody></table>