# First insights into the meiofauna community of a maerl bed in the Bay of Brest (Brittany)

Federica Rebecchi, Daniela Zeppilli, Elisa Baldrighi, Anna Di Cosmo,
Gianluca Polese, Alessandro Pisaniello, Jacques Grall

► To cite this version:

Federica Rebecchi, Daniela Zeppilli, Elisa Baldrighi, Anna Di Cosmo, Gianluca Polese, et al. First insights into the meiofauna community of a maerl bed in the Bay of Brest (Brittany). Scientia Marina, 2022, 86 (1), pp.e024. 10.3989/scimar.05230.024. hal-04207757

HAL Id: hal-04207757

https://hal.science/hal-04207757v1

Submitted on 15 Sep 2023

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
# First insights into the meiofauna community of a maerl bed in the Bay of Brest (Brittany)

Federica Rebecchi<sup>1,2,3,4</sup>, Daniela Zeppilli<sup>1</sup>, Elisa Baldrighi<sup>1,4</sup>, Anna Di Cosmo<sup>2</sup>,
Gianluca Polese<sup>2</sup>, Alessandro Pisaniello<sup>1,2,3,5</sup>, Jacques Grall<sup>3</sup>

**Summary:** Maerl beds, particularly those of Brittany, are important, structurally complex biogenic coastal habitats that form a unique ecosystem with high benthic biodiversity. Although they are relatively well studied throughout Europe, several faunal groups of maerl beds, such as those belonging to the meiofauna, have received little attention. We investigated the meiofaunal abundance, distribution and community structure, with a focus on nematode biomass and diversity, in a maerl area in the Bay of Brest, Brittany, compared with that on a sandy beach (Anse de Dinan, Brittany). Meiofauna was five times more abundant on the maerl bed than on the sandy beach, and 1.5 times more diversified (12 vs. 8 taxa, respectively). Nematode diversity was more than three times higher on the maerl bed than on the sandy beach and showed a distinctive nematode community that was absent from the sandy beach. Maerl beds create more heterogeneous microhabitats and promote a higher diversification of meiofauna and nematode communities than sandy beaches.

**Keywords:** rhodolith beds; Bay of Brest; meiobenthos; Nematoda; biodiversity; taxonomy

## Primeros conocimientos sobre la comunidad meiofáunica del lecho de maerl en la bahía de Brest (Bretaña)

**Resumen:** Los lechos de maerl y, en particular, los de Bretaña, son un importante hábitat costero biogénico y estructuralmente complejo, que forma un ecosistema único con una alta biodiversidad bentónica. A pesar de que varios grupos faunísticos son relativamente bien estudiados en toda Europa, aquellos pertenecientes a la meiofauna han recibido poca atención. Hemos investigado la abundancia, distribución y estructura de la comunidad de la meiofauna, con especial atención a la biomasa y diversidad de nematodos de un área de maerl en la bahía de Brest (Bretaña), en comparación con la de una playa de arena (Anse de Dinan, Bretaña). La meiofauna del maerl fue cinco veces más abundante que la de la playa arenosa, y 1,5 veces más diversificada (12 taxones frente a 8 respectivamente). La diversidad de nematodos del maerl fue más de tres veces mayor que la de la playa arenosa y mostró un único nematodo que, a su vez, resultó ausente en la playa arenosa. Los lechos de maerl crean microhábitats más heterogéneos y promueven una mayor diversificación de la meiofauna y las comunidades de nematodos que los hábitats de playas arenosas.

**Palabras clave:** lechos de rodolitos; bahía de Brest; meiobentos; Nematoda; biodiversidad; taxonomía

**Citation/Como citar este artículo:** Rebecchi F., Zeppilli D., Baldrighi E., Di Cosmo A., Polese G., Pisaniello A., Grall J. 2022. First insights into the meiofauna community of a maerl bed in the Bay of Brest (Brittany). Sci. Mar. 86(1): e024. https://doi.org/10.3989/scimar.05230.024

**Editor:** D. Martin.

**Received:** August 26, 2021. **Accepted:** November 30, 2021. **Published:** March 17, 2022.

**Copyright:** © 2022 CSIC. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) License.

<footnote n="1"><sup>1</sup> Laboratoire Environnement Profond, Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Centre Brest, REM/EEP/LEP, ZI de la Pointe du Diable, CS10070, 29280, Plouzané, France.</footnote>

<footnote>(FR) (Corresponding author) E-mail: rebecchifede@gmail.com. ORCID-iD: https://orcid.org/0000-0003-4762-9263</footnote>

<footnote>(DZ) E-mail: daniela.zeppilli@ifremer.fr. ORCID-iD: https://orcid.org/0000-0002-0809-2566</footnote>

<footnote n="2"><sup>2</sup> Departement of Biology, University of Naples Federico II, MSA campus, Via Cinthia, 80126 Naples, Italy.</footnote>

<footnote>(ADC) E-mail: dicosmo@unina.it. ORCID-iD: https://orcid.org/0000-0002-1018-9957</footnote>

<footnote>(GP) E-mail: gianluca.polese@unina.it. ORCID-iD: https://orcid.org/0000-0002-6322-7769</footnote>

<footnote n="3"><sup>3</sup> Laboratoire des Sciences de l'Environnement Marin (UMS 3113), Institut Universitaire Européen de la Mer/Université de Bretagne Occidentale, Technopôle Brest-Iroise, rue Dumont D'Urville, 29280 Plouzané, France.</footnote>

<footnote>(JG) E-mail: jacques.grall@univ-brest.fr. ORCID-iD: https://orcid.org/0000-0002-3107-6740</footnote>

<footnote n="4"><sup>4</sup> Institute for Biological Resources and Marine Biotechnologies (IRBIM), Italian National Research Council (CNR), Largo Fiera della Pesca 2, 60125 Ancona, Italy.</footnote>

<footnote>(EB) E-mail: elisa.baldrighi@irbim.cnr.it. ORCID-iD: https://orcid.org/0000-0003-3671-8471</footnote>

<footnote n="5"><sup>5</sup> School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand.</footnote>

<footnote>(AP) E-mail: apis527@aucklanduni.ac.nz. ORCID-iD: https://orcid.org/0000-0003-1729-3797</footnote>
## INTRODUCTION

Maerl (or rhodolith) beds are formed by accumu-
lations of living and dead non-geniculate unattached
coralline algae (Foster et al. 2013). They occur on a
wide variety of bottoms, ranging from coarse sand to
fine mud (Grall et al. 2006, Hall-Spencer et al. 2010).
Extensive beds occur on open coasts worldwide, ei-
ther in tide-swept channels or in sheltered areas where
wave action and bioturbation are strong enough to
prevent sediment burial and anoxia from sedimenta-
tion and to move maerl thalli (Foster et al. 2013). In
Europe, maerl beds are reported in the Mediterranean
Sea and all along the Atlantic Ocean coasts, from Por-
tugal to Norway, but are rare in the English Channel,
Irish Sea, North Sea and Baltic Sea (Grall et al. 2006).
Strictly depending on light penetration, they can be
found down to 30 m depth in the northeast Atlantic, to
90–100 m depth in the western Mediterranean, and to
180 m depth in the eastern Mediterranean (BIOMAE-
RL Team 2003).

Maerl beds have been less investigated than other
marine ecosystems such as kelp forests and seagrass
beds (BIOMAERL Team 2003). However, some of
the best-studied maerl beds are located on the Euro-
pean coasts, particularly in Brittany (Hall-Spencer et
al. 2010), where they form a unique ecosystem with a
complex three-dimensional matrix harbouring a higher
benthic biodiversity than on other sublittoral bottoms
(Grall et al. 2006). The associated organisms can either
live inside and on the nodules or burrow into the coarse
gravel and fossil nodules lying beneath the top living
layer (Foster et al. 2013). Many of them are rare, high-
ly specialized species that are mostly confined to this
habitat (BIOMAERL Team 2003), but there are also
juveniles of other organisms, including commercially
important shellfish and fish (Hall-Spencer et al. 2010).

Maerl beds are threatened by anthropogenic ac-
tivities, such as large-scale commercial extraction for
use as a soil conditioner, dredging, bottom trawling,
pollution, eutrophication, aquaculture and invasion of
alien species such as *Crepidula fornicata* Linnaeus,
1758 (BIOMAERL Team 2003). Accordingly, since
1976 they have been included in EU and international
conventions and strategies to preserve fragile marine
ecosystems in Europe (BIOMAERL Team 2003). Fur-
thermore, there are still some major gaps in the knowl-
edge of benthic communities inhabiting maerl beds,
one of them being meiofaunal studies (BIOMAERL
Team 2003).

Meiofauna comprises microscopic protists and
multicellular metazoans living in aquatic sediments
that are retained between sieves with a standard mesh
size of between 1000 and 32 µm (Giere 2009, Zeppilli
et al. 2015a). They play a fundamental role in the ben-
thic food web and in ecosystem functioning because
of their high diversity and abundance, widespread
distribution, rapid generation time and fast metabolic
rates (Zeppilli et al. 2015a and references therein). In
particular, their short generation time and the lack of
pelagic larval dispersion makes them highly sensitive
to natural and anthropogenic environmental alterations

(Zeppilli et al. 2015a). Nematodes are among the most
abundant and diverse meiofaunal metazoans, inhab-
iting all kind of sediments. They are widely used as
indicators in biological monitoring (Semprucci et al.
2018) and are key organisms in the trophic dynamics
of coastal ecosystems, having positive effects on bacte-
rial growth and nutrient recirculation and directly com-
peting with macrofauna for food resources (Leduc and
Probert 2009)

The few studies on meiofauna suggest that maerl
beds support a high biodiversity, including a high diver-
sity of bivalves compared with other substrata (Jackson
et al. 2004) and a new genus of Copepoda from the
Irish west coast (McCormack 2006). Furthermore, a
high species richness of foraminifera on Scottish coasts
has led maerl beds to become an important near-shore
habitat in regional studies of benthic foraminiferal dis-
tribution/ecology (Austin and Cage 2010).

This study aims to characterize (1) the meiofaunal
abundance, vertical distribution and community struc-
ture of a maerl site located in the Bay of Brest, Britta-
ny, France; (2) the taxonomic and functional diversity
of maerl nematode assemblages; and (3) the richness
and diversity of the maerl meiofauna compared with
those from a sandy beach area (Anse de Dinan, Britta-
ny, France).

## MATERIALS AND METHODS

### Study site and sampling strategy

The studied maerl bed is located in the semi-en-
closed Bay of Brest (Brittany, NW France), which
has a total area of 180 km², a maximum tidal am-
plitude of 8 m and an average depth of 8 m (Fig.
1). Water-exchange with the shelf waters (Iroise Sea)
occurs through a narrow (2 km wide) and deep (40
m) channel (Grall et al. 2006), and two rivers (the
Aulne, with a catchment area of 1842 km², and the
Elorn, with a catchment area of 402 km²) contrib-
ute freshwater inputs (Grall et al. 2006). Tidal action
and regular wind-generated swell induce short-term
variability in hydrological factors and enhance water
mass mixing (Grall et al. 2006). Local hydrodynam-
ics influences the sediment composition, which rang-
es from muds to coarse gravels, but there are also
rocky substrata (Grall et al. 2006). Maerl beds cover
30% of the total surface area (Grall et al. 2006).

The sandy beach site is located in the Anse de Di-
nan, Bay of Douarnenez, France (Fig. 1) and is char-
acterized by a median particle size ranging from 140
to 200 mm, a low silt content (0.2%) and a fraction
of dead shells ranging from 2% to 9% (Baldrighi et
al. 2019).

Three replicate samples were collected by SCUBA
divers in April 2012 at the maerl bed site (48°17.627′N,
4°26.470′W, 7 m depth, water temperature of 14°C and
salinity of 33.9; Fig. 1) using Plexiglas corers (6 cm in-
ner diameter) buried down to 5 cm depth. The sediment
cores were sliced into five layers: Maerl Layer at the
top (ML, including maerl without sediment), 0–1, 1–2,
2–3 and 3–4 cm. They were preserved in buffered 4%
<figure><img src="image_2.png" /><figcaption>Fig. 1. – Location of the sampling sites: maerl bed (Bay of Brest) and sandy beach (Anse de Dinan) in Brittany, France.</figcaption></figure>

formalin solution and stained with Rose Bengal (0.5 g l⁻¹). Samples collected below the maerl bed contained poorly sorted, very coarse sands with 3.5% of organic matter. At the sandy beach (48°14.109′N, 4°32.545′W, temperature of 14.4°C, salinity of 35.39; Fig 1), samples were collected in May 2012 at low tide in the intertidal, using Plexiglas corers (3.6 cm inner diameter). The samples consisted of three separates replicates of 15 cm depth cores and contained very well sorted fine sands with 1.5% of organic matter (see Carriço et al. 2013 and Baldrighi et al. 2019 for details). The authors are aware of the different sampling strategy adopted, i.e. a 5 cm sediment depth (maerl bed) vs. a 15 cm sediment depth (sandy beach). However, most meiofaunal organisms inhabit the top 5 cm of sediment (e.g. Ingels and Vanreusel 2013), allowing us to assume that comparisons between the two environments would not be substantially affected.

## Meiofaunal and nematode analyses

All samples were sieved through 1000 µm and 32 µm mesh sizes. Meiofaunal organisms were extracted by Ludox centrifugation following Danovaro (2010), counted and classified to the highest taxonomic level using a stereomicroscope. At least 100 nematodes from each replicate were picked out randomly and mounted on permanent slides after formalin-ethanol-glycerol treatment for identification to the genus level with an optical microscope according to Platt and Warwick (1988) and the recent literature available (NeMys database, Bezerra et al. 2021). Species richness (SR), expected number of genera (51) and diversity indices

(Shannon, H', Margalef D, Pielou evenness and J') were calculated for both meiofauna and nematodes with the DIVERSE routine (PRIMER 6+; Clarke and Gorley 2006). The nematodes were divided into four trophic groups following Wieser (1953): (1A) selective (bacterial) feeders with no buccal cavity or a fine tubular one; (1B) non-selective deposit feeders with a large but unarmed buccal cavity; (2A) epistrate or epigrowth (diatom) feeders with a scraping tooth or teeth in the buccal cavity; and (2B) predators/omnivores with a buccal cavity with large jaws. The index of trophic diversity (ITD) was calculated considering the relative contribution of each trophic group to the total (Gambi et al. 2003). Nematode biomass was calculated by biovolume, estimated from all specimens per replicate (Andrassy 1956). Then, dry weight (µg DW) was estimated by multiplying each body volume by an average density (1.13 g cm⁻³), and finally the biomass was expressed as carbon content (µg of C/10 cm²), which was considered to be 40% of dry weight (Feller and Warwick 1988).

## Statistical analysis

Differences in total meiofaunal abundance, total nematode biomass, nematode diversity between layers, total meiofaunal abundance and total nematode biomass between the maerl bed and the sandy beach were assessed by one-way analyses of variance (ANOVA). Prior to the ANOVAs, the homogeneity of variances was assessed by the Anderson-Darling test and, when necessary, data were square-root transformed. Tukey's HSD test was performed to assess significant
<figure><img src="image_3.png" /><figcaption>Fig. 2. - A, vertical distribution of total meiofaunal abundance in the maerl bed (ind/10 cm²). B, meiofaunal community structure in the maerl bed (as percentages of dominant higher taxa). Horizontal bars are standard deviations. ML, Maerl Layer at the top (including maerl without sediment).</figcaption></figure>

between-level effects. The ANOVAs and Turkey's test were performed using the STATISTICA V.10 software. A one-way analysis of similarities (ANO-SIM) was used to assess between-layer differences in meiofauna community structure and nematode composition. The SIMPER routine (cut-off of 90%, on fourth-root transformed data) was used to determine the contribution of each meiofaunal taxon and nematode species to the total dissimilarity. ANOSIM and SIMPER analyses were performed using Primer 6+ (Clarke and Gorley 2006).

## RESULTS

### Maerl meiofauna community

The total meiofaunal abundance was 1986±457 ind/10 cm². The highest mean abundance occurred in layer 1–2 (748±466 ind/10 cm²) and decreased with increasing depth, being the lowest in layer 3–4 (179±25 ind/10 cm²) (Fig. 2A). The ML and layers

0–1 and 1–2 showed a significantly higher abundance than the deepest layer (ANOVA, p<0.05).

A total of 12 (8±1) taxa characterized the maerl station, including Nematoda, Copepoda + nauplii, Polychaeta, Ostracoda, Kinorhyncha, Oligochaeta, Amphipoda, Cladocera, Gastropoda, Tardigrada, Isopoda and Foraminifera. From layer 0–1 to 3–4, Nematoda were the most abundant (82%–97%), followed by Copepoda (1%–9%) and their nauplii (1%–7%). Polychaeta accounted for 1% in layers 0–1 and 1–2 and Foraminifera for 1% in layer 0–1. In the ML, Copepoda (31%) with their nauplii (60%) were the most abundant (91%), followed by Nematoda (7%), Polychaeta (2%) and Ostracoda (1%) (Fig. 2B). Kinorhyncha, Oligochaeta, Amphipoda, Cladocera, Gastropoda, Tardigrada and Isopoda accounted for less than 1% of the total abundance at all layers and are together indicated as “other taxa”. The community structure differed significantly between sediment layers (ANOSIM, R=44%; P=0.012) (Table S1A), with the differences being mainly due to the increasing abundance of Nematoda and the decreasing
<figure><img src="image_4.png" /><figcaption>Fig. 3. – A. Vertical distribution of nematode biomass. B. Expected genus number (EG (51)). C. Most abundant nematode genera. D. Nematode trophic structure.</figcaption></figure>

ing abundance of Copepoda along the sediment profile (SIMPER, Table S2). The sediment layers showed dis-similarities ranging from 30% (0–1 vs. 1–2 cm) to 74% (2–3 vs. 3–4 cm) (SIMPER, Table S1A).

## The maerl nematode community

The mean total nematode biomass was 108.2±41.9 µg of C/10 cm². It increased along the sediment profile from 2.7±1.2 µg of C/10 cm² in the ML to 40.3±10.9 µg of C/10 cm² in layer 2–3 cm (Fig. 3A). There were 78 genera and 22 families of nematodes (Table S3). The expected number of genera (51) ranged from 15.2±0.5 in layer 3–4 to 20.5±4.9 in layer 0–1, showing a decreasing trend along the sediment profile (Fig. 3B, Table S4). The Shannon index ranged from 2.3±0.3 in layer 1–2 to 2.7±0.3 in the ML, and the Pielou index ranged from 0.7±0.1 in layers 0–1, 1–2 and 2–3 to 0.9±0 in the ML, indicating that all genera were equally represented (Table S4). There were no significant between-layer differences in any diversity index.

Linhomoeidae was the most abundant family (36%), followed by Desmodoridae (30%), Chromadoridae (9%), Comesomatidae (8%) and Xyalidae (4%). The most abundant genera were *Terschellingia* (21%).

*Spirinia* (13%), *Molgolaimus* (14%), *Metalinhomoeus* (12%) and *Sabatieria* (7%). *Molgolaimus* was more abundant (39%) in layer 0–1 and decreased with depth to 1% in layer 3–4, and *Spilophorella* decreased with depth from 20% in the ML to 0% in layer 2–3. *Terschellingia* increased in abundance with depth from 1% in the ML to 35% in layer 3–4, and *Sabatieria* increased in abundance with depth from 1% in the ML to 16% in layer 2–3. *Metalinhomoeus* also increased in abundance with depth from 4% in the ML to 23% in layer 3–4. *Spirinia* increased in abundance from 2% in the ML to 28% in layer 1–2 and then dropped to 6% in layer 3–4 (Fig. 3C).

The nematode composition in the ML and layer 0–1 differed significantly from those at all other layers (ANOSIM, Global R=37%: p=0.004, Table S1B), mostly owing to the presence of *Terschellingia*, *Spirinia* and *Perspiria* at the deeper layers and *Molgolaimus* in the top 1 cm (SIMPER analysis, Table S5). The trophic structure of the nematode assemblage was 1A (40%), 2A (30%), 1B (25%), and 2B (5%), although the contribution of some trophic groups changed along the sediment profile. 1A were less abundant in the ML (18%) and reached the highest abundance in layer 0–1 (53%), while 1B and 2B did not change significantly across layers (Fig. 3D). On the other hand, 2A were
dominant in the ML (58%), showing the highest biomass (38.4 µg of C/10 cm²). 1B and 2B showed biomasses of 26.1 and 27.0 µg of C/10 cm², respectively, and 1A showed the lowest biomass (16.7 µg of C/10 cm²).

## Maerl bed vs. sandy beach meiofauna

Total meiofaunal density in the maerl bed was five times higher than on the sandy beach (1.986±457 ind/10 cm² vs. 384±16 ind/10 cm², respectively; ANOVA, p<0.05) (Fig. 4). Twelve higher taxa were identified in the maerl bed vs. 8 on the sandy beach (Fig. 4), where Nematoda was the most abundant (96%), followed by Copepoda (3%). Cumacea, Gastrotricha, Isopoda, Ostracoda, Platyhelminthes and Tardigrada accounted for less than 1%. Total nematode biomass was significantly higher in the maerl bed than on the sandy beach (108.2±41.9 and 47.6±2.1 µg of C/10 cm²; ANOVA, p<0.05). Nematode diversity in the maerl bed was more than three times higher than on the sandy beach, where 11 families and 20 genera were identified (Fig. 4), including *Richtersia* (51%), *Trileptum* (9%), *Daptonema* and *Omicronema* (8% each) as the most abundant. Overall, 66 and 8 nematode genera were exclusive to the maerl bed and the sandy beach, respectively, with 12 being shared (Table S6). 1A dominated in the maerl bed (40%) and 1B on the sandy beach (72%). Overall, the maerl bed showed a lower ITD (0.32) than the sandy beach (0.62), indicating a greater trophic diversity in the maerl bed (Table S6).

# DISCUSSION

## Maerl meiofaunal and nematode assemblages

The high maerl meiofaunal abundance recorded in the Bay of Brest was similar to that found in other structurally complex and perennial habitats such as seagrass beds (Novack 1989, Pusceddu et al. 2014) and similar micro-habitat rich environments such as coral sediments (Semprucci et al. 2013). The highest meiofaunal abundance was found in layer 1–2, and it progressively decreased along the sediment profile. Conversely, meiofauna is often concentrated in the first few centimetres of sediment (Giere 2009). In the maerl bed, the meiofauna distribution likely responds to its complex architecture, allowing a higher organic and oxygen content subsuperficially. This complexity also protects the sediment below, because meiofaunal organisms are less exposed to hydrodynamic perturbations. Indeed, the low erosion, combined with organic accumulation and dispersal lowering, may favour an increase in abundance subsuperficially. Conversely, taxa living on the surface or between the maerl thalli are less protected from current or wave actions (Martínez et al. 2021).

Among the 12 taxa identified, nematodes were the most abundant in all sediment layers except in the ML, where the community was dominated by Copepoda with their nauplii. Nematodes are well-known to penetrate deeply into sediments thanks to their specialized morphology and high tolerance to anaerobic conditions

<figure><img src="image_5.png" /><figcaption>Fig. 4. – Shannon index (H'), nematode biomass (µg of C/10 cm²), trophic diversity index (ITD) values, expected genus number (EG (51)), equitability evenness (J'), meiofaunal abundance and number of higher meiofauna (N° taxa). Vertical bars are standard deviations.</figcaption></figure>
(Heip et al. 1985), while hydrodynamism can also contribute to the dispersal of the specimens into deeper layers (Zeppilli et al. 2014). Consequently, nematodes were less abundant in the ML, possibly because of the low shelter inherent to its particular architecture, but probably also to a higher predation pressure (Grall et al. 2006).

Copepods and nauplii were particularly abundant in the ML, resembling coral sediment assemblages (Semprucci et al. 2013). This could be related to the additional food resources (macroepiphytic algae and microphytobenthos production) associated with maerl beds (Grall et al. 2006). In addition, the swimming ability of crustaceans, compared with other meiofaunal groups, allows them to speedily return to the seafloor after being resuspended in the water column by current or waves (e.g. Colangelo et al. 2001, Zeppilli et al. 2015b). However, their numbers decreased along the sediment profile, despite the coarse sediment that has been suggested to promote their presence (Colangelo et al. 2001), likely due to their high sensitivity to oxygen depletion or anaemia, unlike nematodes (Moodley et al. 2000).

Some genera of Chromadoridae are almost entirely restricted to upper sediment layers (Platt 1977). Accordingly, the epistrate feeders *Spilophorella* and *Spirinia* showed high abundances in the ML and layer 1–2, respectively, and decreased along the sediment profile, probably because of lowering food availability (Pusceddu et al. 2009). *Terschellingia* and *Sabatiera* penetrated deep into the sediment, having their highest abundances in layers 3–4 and 2–3, respectively. *Terschellingia*, a selective deposit feeder, is usually found in anoxic sediments (Wieser 1960). *Sabatieria*, a non-selective deposit feeder displaying a wide range of ecological preferences (Steyaert 1999), is also known to be a facultative anaerobic organism, a trait allowing it to inhabit suboxic or anoxic sediment layers, so it is thus a common deeper-living nematode (Jensen 1987). *Metalinhomoeus* was present in all sediment layers, but was particularly abundant in layer 3–4. This genus is known to be associated with subtidal silt or muddy sediments (Wieser 1960), being frequent in sediments with low oxygen levels (Heip et al. 1985). It also has a body morphology that allows it to dig quickly up and down into the sediment, passing easily from reduced to well-oxygenated zones (Jensen 1987). Surprisingly, we found no families typically associated with 3D complex substrates, such as Epsilon nematidae and Draconematidae from corals or hard substrates (Raes et al. 2008, Zeppilli et al. 2015b). Therefore, our data support the hypothesis that maerl nematodes benefit mainly from the sediments below the bed, instead of the 3D rhodoliths, which mainly act as a protective layer for the sediments and assemblages below. Moreover, all trophic groups were equally represented in all layers, allowing us to suggest possible differences in food sources along the sediment profile. This may well help reduce the number of competitive interactions, while allowing the different feeding groups to coexist in small sediment patches.

## Maerl bed vs. sandy beach

Maerl beds are known to harbour higher macrofaunal biodiversity than bare sediments (Foster et al. 2013), and meiofauna is no exception. In the maerl bed, its abundance was five times higher, and its taxa diversity 1.5 times higher than on the sandy beach. Obviously, nematodes were also more numerous (three times), as was the number of exclusive genera (66). The functional diversity (i.e. trophic diversity) was also higher in the maerl bed. All trophic groups were represented: bacterial and epistrate feeders (1A and 2A respectively) dominated in the maerl bed, while the non-selective deposit feeders (1B) dominated on the sandy beach. Thus, maerl beds seemed to host a rich meiofaunal community and a unique and peculiar nematode community, which is clearly distinguishable from those inhabiting sandy beach ecosystems. Accordingly, maerl beds seem to harbour a rich and specific meiofaunal community that may serve as potential prey for these predator/omnivore nematodes. The physical presence of complex maerl thalli, combined with the numerous resources provided, may explain the difference in meiofaunal diversity between these habitats. Moreover, the sandy beach samples were collected at low tide in the intertidal. This may have also affected the community composition and richness, since only well-adapted fauna can survive the extreme conditions arising from long-term exposure (e.g. higher radiation, salinity and oxygen availability variation) (Baldrighi et al. 2019 and literature therein).

Our study documented novel findings on the abundance, structure and diversity of the meiofauna and nematode communities characterizing the maerl beds from the Bay of Brest. Our results suggest that maerl beds create a more heterogeneous environment, richer in microhabitats, that promotes highly diversified meiofaunal and nematode assemblages in the sediments below, which proved to be particularly rich when compared with more homogenous environments lacking the protective rhodolith layer (e.g. a sandy beach). Maerl beds, which have been largely neglected in meiofaunal studies, have been shown to harbour high meiofaunal assemblages with a very complex structure and a high functional diversity. Therefore, their protection may be crucial for marine biodiversity preservation.

## FUNDING

This work was funded by the IMPECAPE (OFB CNRS Programme). FR was supported by the University of Naples Federico II and Compagnia di San Paolo scholarship.

## ACKNOWLEDGEMENTS

We would like to thank the Albert Lucas crew as well as Erwan Amice, Thierry Lebec and Nolwenn Quillien for helping with sampling. We also thank Dr Carmen Ferrà for the Spanish translation.
REFERENCES

Andrassy I. 1956. Die Rauminhalts-und Gewichtsbestimmung der Fadenwürmer (Nematoden). Acta. Zool. Hung. 2: 1-5.

Austin W.E.N., Cage A.G. 2010. High benthic foraminiferal species counts in a Clyde Sea mael bed, western Scotland. Geolog. Soc. London. Spec. Pub. 344: 83-88.
https://doi.org/10.1144/SP344.8

BIOMAERL Team: Barbera J., Bordehore C., Borg J.A., et al. 2003. Conservation and management of northeast Atlantic and Mediterranean maelr beds. Aquat. Conserv. Mar. Fresh. Ecosyst. 13: 65-76.
https://doi.org/10.1002/aqc.569

Baldrighi E., Grall J., Quillien N., et al. 2019. Meiofauna communities' response to an anthropogenic pressure: The case study of green macroalgal bloom on sandy beach in Brittany. Est. Coast. Shelf Sci. 227: 106326.
https://doi.org/10.1016/j.ecss.2019.106326

Bezerra T.N., Eisendle U., Hodda M., et al. 2021. Nemys: World Database of Nematodes. Accessed at http://nemys.ugent.be on 05/06/2021.
https://doi.org/10.14284/366

Carriço R., Zeppilli D., Quillien N., et al. 2013. Can meiofauna be a good biological indicator of the impacts of eutrophication caused by green macroalgal blooms? An Aod. Cah. Nat. Obs. Mar. 2: 9-16.

Clarke K.R., Gorley R.N. 2006. PRIMER V6: User Manual/Tutorial. PRIMER-E, Plymouth, 93 pp.

Colangelo M.A., Bertasi F., Dall'Olio P., Ceccherelli V. H. 2001. Meiofaunal biodiversity on hydrothermal seepage off Panarea (Aeolian islands, Tyrrenian sea). In: Faranda F.M, Guglielmo L., Spezie G. (eds), Mediterranean Ecosystems: Structures and Processes. Springer Verlag, pp. 353-359.
https://doi.org/10.1007/978-88-470-2105-1_46

Danovaro R. 2010. Methods for the Study of Deep-Sea Sediments, Their Functioning and Biodiversity. CRC Press Boca Raton, 458 pp.
https://doi.org/10.1201/9781439811382

Feller R.J., Warwick R.M. 1988. "Energetics". In: Higgin, R.P., Thiel, H. (eds), Introduction to the Study of Meiofauna. Washington, DC. Smithsonian Institution. pp. 181-196.

Foster M.S., Amado Filho G.M., Kamenos N.A., et al. 2013. Rhodoliths and rhodolith beds. Smithsonian Contr. Mar. Sci. 39: 143-55.

Gambi C., Vanreusel A., Danovaro R. 2003. Biodiversity of nematode assemblages from deepsea sediments of the Atacama Slope and Trench (South Pacific Ocean). Deep Sea Res. I: Oceanogr. Res. Pap. 50: 103-117.
https://doi.org/10.1016/S0967-0637(02)00143-7

Giere O. 2009. Meiobenthology. The microscopic motile fauna of aquatic sediments. Springer-Verlag, Berlin 527 pp.

Grall J., Le Loc'h F., Guyonnet B., Riera P. 2006. Community structure and food web based on stable isotopes (δ15N and δ13C) analysis of a North Eastern Atlantic maelr bed. J. Exp. Mar. Biol. Ecol. 338: 1-15.
https://doi.org/10.1016/j.jembe.2006.06.013

Hall-Spencer J., Kelly J., Maggs C.A. 2010. Background document on maelr beds. OSPAR Commission, London.

Heip C.H.R., Vincx M., Vranken G. 1985. The ecology of marine nematodes. Oceanogr. Mar. Biol. Ann. Rev. 23: 399-489.

Ingels J., Vanreusel A. 2013. The importance of different spatial scales in determining structure and function of deep-sea infauna communities. Biogeosciences Discuss 10: C796-C807.
https://doi.org/10.5194/bgd-10-195-2013

Jackson C.M., Kamenos N.A., Moore P.G., Young M. 2004. Meiofaunal bivalves in maelr and other substrata; their diversity and community structure. Ophelia 58: 48-60.
https://doi.org/10.1080/00785236.2004.10410212

Jensen P. 1987. Differences in microhabitat, abundance, biomass and body size between oxybiotic and thiobiotic free-living marine nematodes. Oecologia 71: 564-567.
https://doi.org/10.1007/BF00379298

Leduc D., Probert P.K. 2009. The effect of bacterivorous nematodes on detritus incorporation by macrofaunal detritivores: A study using stable isotope and fatty acid analyses. J. Exp. Mar. Biol. Ecol. 37: 130-139.
https://doi.org/10.1016/j.jembe.2009.01.011

Linnaeus C. 1758. Systema Naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Laurentius Salvius, Holmae, 824 pp.
https://doi.org/10.5962/bhl title.542

McCormack E. 2006. Carraroenia ruthae gen. et sp. nov. (Copepoda, Harpacticoida, Laophontidae) from maelr substrates of the Irish west coast. Zootaxa 1202: 39-52.
https://doi.org/10.11646/zootaxa.1202.1.4

Moodley L., Chen GT., Heip C., Vincx M. 2000. Vertical distribution of meiofauna in sediments from contrasting sites in the Adriatic Sea: clues to the role of abiotic versus biotic control. Ophelia 53: 203-212.
https://doi.org/10.1080/00785326.2000.10409450

Martínez A., García-Gómez G., García-Herrero Á. et al. 2021. Habitat differences filter functional diversity of low dispersive microscopic animals (Acari, Halacaridae). Hydrobiologia 848: 2681-2698.
https://doi.org/10.1007/s10750-021-04586-x

Novack R. 1989. Ecology of Nematodes in the Mediterranean Seagrass *Posidonia oceanica* (L.) Delile 1. General part and faunistics of the nematode community. Mar. Ecol. 10: 335-363.
https://doi.org/10.1111/j.1439-0485.1989.tb00077.x

Platt H.M. 1977. Vertical and horizontal distribution of free-living marine nematodes from Strangford Lough, Northern Ireland. Cah. Biol. Mar. 18: 261-273.

Platt H.M., Warwick R.M. 1988. Free-living Marine Nematodes. Part II: British Chromadorids. Brill Academic Pub., 502 pp.
Pusceddu A., Dell'Anno A., Fabiano M., Danovaro, R. 2009. Quantity and bioavailability of sediment organic matter as signatures of benthic trophic status. Mar. Ecol. Progr. Ser. 375: 41-52.
https://doi.org/10.3354/meps07735

Pusceddu A., Gambi C., Corinaldesi C., Scopa M., Danovaro R. 2014. Relationships between Meiofaunal Biodiversity and Prokaryotic Heterotrophic Production in Different Tropical Habitats and Oceanic Regions. PLoS ONE 9: e91056.
https://doi.org/10.1371/journal.pone.0091056

Raes M., Decraemer W., Vanreusel A. 2008. Walking with worms: coral-associated epifaunal nematodes. J. Biogeog. 35: 2207-2222.
https://doi.org/10.1111/j.1365-2699.2008.01945.x

Semprucci F., Colantoni P., Baldelli G., et al. 2013. Meiofauna associated with coral sediments in the Maldivian subtidal habitats (Indian Ocean). Mar. Biodivers. 43: 189-198.
https://doi.org/10.1007/s12526-013-0146-7

Semprucci F., Balsamo M., Apolloni L., Sandulli R. 2018. Assessment of ecological quality status along the Apulian coasts (eastern Mediterranean Sea) based on meiobenthic and nematode assemblages. Mar. Biodivers. 48: 105-115.
https://doi.org/10.1007/s12526-017-0745-9

Steyaert M., Garner N., Van Gansbeke D., Vincx M. 1999. Nematode communities from the North Sea: environmental controls on species diversity and vertical distribution within the sediment. J. Mar. Biol. Assoc. UK 79: 253-264.
https://doi.org/10.1017/S0025315498000289

Wieser W. 1953. Die beziehung zwischen Mundhöhlenstalt, Ernährungsweise und vorkommen bei freilebenden marinen Nematoden. Ark. Zool. 4: 439-484.

Wieser W. 1960. Benthic studies in Buzzards Bay. II. The meiofauna. Limnol. Oceanogr. 5: 121-137.
https://doi.org/10.4319/lo.1960.5.2.0121

Zeppilli D., Bongiorni L., Santos R.S., Vanreusel A. 2014. Changes in Nematode Communities in Different Physiographic Sites of the Condor Seamount (North-East Atlantic Ocean) and Adjacent Sediments. PLoS ONE 9(12):e115601.
https://doi.org/10.1371/journal.pone.0115601

Zeppilli D., Sarrazin J., Leduc D. Arbizu P.M., et al. 2015a. Is the meiofauna a good indicator for climate change and anthropogenic impacts? Mar. Biodivers. 45: 505-535.
https://doi.org/10.1007/s12526-015-0359-z

Zeppilli D., Vanreusel A., Pradillon F., et al. 2015b. Rapid colonisation by nematodes on organic and inorganic substrata deployed at the deep-sea Lucky Strike hydrothermal vent field (Mid-Atlantic Ridge). Mar. Biodivers. 45: 489-504.
https://doi.org/10.1007/s12526-015-0348-2
SUPPLEMENTARY MATERIAL

The following supplementary material is available
through the online version of this article and at the fol-
lowing link: http://scimar.icm.csic.es/scimar/supplm/
sm05230esm.pdf

Table S1. – ANOSIM (R statistic), significance level (P) and SIMPER results (Diss., Dissimilarity %). A. most abundant higher meiofaunal taxa. B. nematode species.

Table S2. – SIMPER analysis showing the contribution of meiofaunal taxa to between-layer dissimilarity. Contrib.%, contribution %; Cum.%, cumulative %.

Table S3. – List of nematode families, genera and putative species found in the maerl bed.

Table S4. – Nematode diversity indices in the maerl bed: species richness (SR), Margalef diversity (D), Pielou evenness (J'), expected genus number (EG(51)) and Shannon index (H').

Table S5. – SIMPER analysis showing the contribution of nematode species to between-layer dissimilarity. The ten most contributing taxa are reported. The following abbreviations were used: Contrib.%, contribution%; Cum.%, cumulative %.

Table S6. – Meiofaunal abundance, number of higher taxa, nem-
atode biomass, diversity (Shannon index (H'), equitability
evenness (J'), expected genus number (EG(51)) and trophic
diversity index (ITD)). List of exclusive and shared genera
of nematodes between the maerl bed and the sandy beach.
# First insights into the meiofauna community of a maerl bed in the Bay of Brest (Brittany)

Federica Rebecchi, Daniela Zeppilli, Elisa Baldrighi, Anna Di Cosmo, Gianluca Polese, Alessandro Pisaniello, Jacques Grall

Supplementary material
<table><caption>Table S1. – ANOSIM (R statistic), significance level (P) and SIMPER results (Diss., Dissimilarity %). A. most abundant higher meiofaunal taxa. B. nematode species.</caption><thead><tr><th colspan="4">A</th></tr><tr><th>Group</th><th>R statistic %</th><th>P</th><th>Diss. %</th></tr></thead><tbody><tr><td>ML, 0-1 cm</td><td>41</td><td>0.01</td><td>39</td></tr><tr><td>ML, 1-2 cm</td><td>37</td><td>0.01</td><td>39</td></tr><tr><td>ML, 2-3 cm</td><td>15</td><td>0.02</td><td>59</td></tr><tr><td>ML, 3-4 cm</td><td>42</td><td>0.02</td><td>32</td></tr><tr><td>0-1 cm, 1-2 cm</td><td>59</td><td>0.01</td><td>30</td></tr><tr><td>0-1 cm, 3-4 cm</td><td>100</td><td>0.01</td><td>63</td></tr><tr><td>1-2 cm, 2-3 cm</td><td>22</td><td>0.02</td><td>49</td></tr><tr><td>1-2 cm, 3-4 cm</td><td>100</td><td>0.01</td><td>67</td></tr><tr><td>2-3 cm, 3-4 cm</td><td>17</td><td>0.04</td><td>74</td></tr></tbody></table>

<table><thead><tr><th colspan="4">B</th></tr><tr><th>Group</th><th>R statistic %</th><th>P</th><th>Diss. %</th></tr></thead><tbody><tr><td>ML, 0-1 cm</td><td>33</td><td>0.02</td><td>65</td></tr><tr><td>ML, 1-2 cm</td><td>67</td><td>0.01</td><td>74</td></tr><tr><td>ML, 2-3 cm</td><td>67</td><td>0.01</td><td>73</td></tr><tr><td>ML, 3-4 cm</td><td>83</td><td>0.01</td><td>75</td></tr><tr><td>0-1 cm, 1-2 cm</td><td>30</td><td>0.02</td><td>52</td></tr><tr><td>0-1 cm, 2-3 cm</td><td>44</td><td>0.01</td><td>58</td></tr><tr><td>0-1 cm, 3-4 cm</td><td>83</td><td>0.01</td><td>60</td></tr><tr><td>1-2 cm, 2-3 cm</td><td>19</td><td>0.03</td><td>51</td></tr><tr><td>1-2 cm, 3-4 cm</td><td>25</td><td>0.04</td><td>47</td></tr><tr><td>2-3 cm, 3-4 cm</td><td>8</td><td>0.04</td><td>49</td></tr></tbody></table>
<table><caption>Table S2. – SIMPER analysis showing the contribution of meiofaunal taxa to between-layer dissimilarity. Contrib.%, contribution %; Cum.%, cumulative %.</caption><thead><tr><th colspan="3">Groups ML & 0-1 cm</th><th colspan="3">Groups ML & 1-2 cm</th><th colspan="3">Groups ML & 2-3 cm</th><th colspan="3">Groups ML & 3-4 cm</th></tr><tr><th>Taxon</th><th>Contrib%</th><th>Cum.%</th><th>Taxon</th><th>Contrib%</th><th>Cum.%</th><th>Taxon</th><th>Contrib%</th><th>Cum.%</th><th>Taxon</th><th>Contrib%</th><th>Cum.%</th></tr></thead><tbody><tr><td>Nematoda</td><td>45.78</td><td>45.78</td><td>nauplii</td><td>32.3</td><td>32.3</td><td>Nematoda</td><td>31.98</td><td>31.98</td><td>Nematoda</td><td>33.28</td><td>33.28</td></tr><tr><td>nauplii</td><td>21.84</td><td>67.62</td><td>Copepoda</td><td>26.64</td><td>58.94</td><td>nauplii</td><td>27.64</td><td>59.62</td><td>nauplii</td><td>32.16</td><td>65.44</td></tr><tr><td>Copepoda</td><td>15.26</td><td>82.87</td><td>Nematoda</td><td>20.67</td><td>79.61</td><td>Copepoda</td><td>23.97</td><td>83.6</td><td>Copepoda</td><td>16.84</td><td>82.28</td></tr><tr><td>Foraminifera</td><td>4.93</td><td>87.8</td><td>Polichaeta</td><td>6.61</td><td>86.22</td><td>Polichaeta</td><td>6.58</td><td>90.18</td><td>Ostracoda</td><td>8.16</td><td>90.44</td></tr><tr><td>Ostracoda</td><td>3.86</td><td>91.66</td><td>Ostracoda</td><td>4.94</td><td>91.15</td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody><thead><tr><th colspan="3">Groups 0-1 cm & 1-2 cm</th><th colspan="3">Groups 0-1 cm & 2-3 cm</th><th colspan="3">Groups 0-1 cm & 3-4 cm</th><th colspan="3">Groups 1-2 cm & 2-3 cm</th></tr><tr><th>Taxon</th><th>Contrib%</th><th>Cum.%</th><th>Taxon</th><th>Contrib%</th><th>Cum.%</th><th>Taxon</th><th>Contrib%</th><th>Cum.%</th><th>Taxon</th><th>Contrib%</th><th>Cum.%</th></tr></thead><tbody><tr><td>Nematoda</td><td>52.33</td><td>52.33</td><td>Nematoda</td><td>69.7</td><td>69.7</td><td>Nematoda</td><td>42.81</td><td>42.81</td><td>Nematoda</td><td>62.73</td><td>62.73</td></tr><tr><td>nauplii</td><td>12.48</td><td>64.81</td><td>Copepoda</td><td>8.23</td><td>77.93</td><td>nauplii</td><td>28.38</td><td>71.19</td><td>nauplii</td><td>11.79</td><td>74.52</td></tr><tr><td>Copepoda</td><td>10.92</td><td>75.73</td><td>Polichaeta</td><td>5.99</td><td>83.92</td><td>Copepoda</td><td>17.08</td><td>88.27</td><td>Copepoda</td><td>10.38</td><td>84.9</td></tr><tr><td>Foraminifera</td><td>9.03</td><td>84.76</td><td>Foraminifera</td><td>5.23</td><td>89.14</td><td>Foraminifera</td><td>2.86</td><td>91.13</td><td>Polichaeta</td><td>4.26</td><td>89.16</td></tr><tr><td>Polichaeta</td><td>7.34</td><td>92.1</td><td>nauplii</td><td>4.99</td><td>94.13</td><td></td><td></td><td></td><td>Foraminifera</td><td>4.16</td><td>93.32</td></tr></tbody><thead><tr><th colspan="3">Groups 1-2 cm & 3-4 cm</th><th colspan="3">Groups 2-3 cm & 3-4 cm</th><th colspan="3"></th><th colspan="3"></th></tr><tr><th>Taxon</th><th>Contrib%</th><th>Cum %</th><th>Taxon</th><th>Contrib%</th><th>Cum.%</th><th>Taxon</th><th>Contrib%</th><th>Cum.%</th><th>Taxon</th><th>Contrib%</th><th>Cum.%</th></tr></thead><tbody><tr><td>nauplii</td><td>35.24</td><td>35.24</td><td>nauplii</td><td>39.66</td><td>39.66</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Nematoda</td><td>27.14</td><td>62.39</td><td>Copepoda</td><td>27.44</td><td>67.09</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Copepoda</td><td>23.57</td><td>85.96</td><td>Nematoda</td><td>17.44</td><td>84.54</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Polichaeta</td><td>4.36</td><td>90.32</td><td>Polichaeta</td><td>5.6</td><td>90.14</td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

<table><caption>Table S3. – List of nematode families, genera and putative species found in the maerl bed.</caption><thead><tr><th>Family</th><th>Genus</th><th>Species</th></tr></thead><tbody><tr><td>Chromadoridae</td><td>Acantholaimus</td><td>Acantholaimus sp1</td></tr><tr><td>Chromadoridae</td><td>Actinonema</td><td>Actinonema sp1</td></tr><tr><td>Leptolaimidae</td><td>Antomicron</td><td>Antomicron sp1</td></tr><tr><td>Diplopeltidae</td><td>Campylaimus</td><td>Campylaimus sp1</td></tr><tr><td>Anticomidae</td><td>Cephalanticoma</td><td>Cephalanticoma sp1</td></tr><tr><td>Chromadoridae</td><td>Chromadora</td><td>Chromadora sp1</td></tr><tr><td>Chromadoridae</td><td>Chromadora</td><td>Chromadora sp2</td></tr><tr><td>Chromadoridae</td><td>Chromadorella</td><td>Chromadorella sp1</td></tr><tr><td>Chromadoridae</td><td>Chromadoridae spp.</td><td>Chromadoridae spp.</td></tr><tr><td>Chromadoridae</td><td>Chromadorita</td><td>Chromadorita sp1</td></tr><tr><td>Xyalidae</td><td>Cobbia</td><td>Cobbia sp1</td></tr><tr><td>Comesomatidae</td><td>Comesomatidae spp.</td><td>Comesomatidae spp.</td></tr><tr><td>Comesomatidae</td><td>Comesoma</td><td>Comesoma sp1</td></tr><tr><td>Comesomatidae</td><td>Comesomoides</td><td>Comesomoides sp1</td></tr><tr><td>Cyartonematidae</td><td>Cyartonema</td><td>Cyartonema sp1</td></tr><tr><td>Xyalidae</td><td>Daptonema</td><td>Daptonema sp1</td></tr><tr><td>Desmoscolecidae</td><td>Desmoscolex</td><td>Desmoscolex sp1</td></tr><tr><td>Camacolaimidae</td><td>Diodontolaimus</td><td>Diodontolaimus sp1</td></tr><tr><td>Comesomatidae</td><td>Dorylaimopsis</td><td>Dorylaimopsis sp1</td></tr><tr><td>Draconematidae</td><td>Draconema</td><td>Draconema sp1</td></tr><tr><td>Chromadoridae</td><td>Euchromadora</td><td>Euchromadora sp1</td></tr><tr><td>Linhomoeidae</td><td>Eumorpholaimus</td><td>Eumorpholaimus sp1</td></tr><tr><td>Enchelidiidae</td><td>Eurystomina</td><td>Eurystomina sp1</td></tr></tbody></table>
<table><thead><tr><th>Family</th><th>Genus</th><th>Species</th></tr></thead><tbody><tr><td>Oncholaimidae</td><td>Filoncholaimus</td><td>Filoncholaimus sp1</td></tr><tr><td>Oxystominidae</td><td>Halalaimus</td><td>Halalaimus sp1</td></tr><tr><td>Leptolaimidae</td><td>Halaphanolaimus</td><td>Halaphanolaimus sp1</td></tr><tr><td>Selachinematidae</td><td>Halichoanolaimus</td><td>Halichoanolaimus sp1</td></tr><tr><td>Monhysteridae</td><td>Halomonhystera</td><td>Halomonhystera sp1</td></tr><tr><td>Chromadoridae</td><td>Karkinochromadora</td><td>Karkinochromadora sp1</td></tr><tr><td>Cyatholaimidae</td><td>Kraspedonema</td><td>Kraspedonema sp1</td></tr><tr><td>Comesomatidae</td><td>Laimella</td><td>Laimella sp1</td></tr><tr><td>Leptolaimidae</td><td>Leptolaimus</td><td>Leptolaimus sp1</td></tr><tr><td>Leptolaimidae</td><td>Leptolaimus</td><td>Leptolaimus sp2</td></tr><tr><td>Linhomoeidae</td><td>Linhomoeus spp.</td><td>Linhomoeus spp.</td></tr><tr><td>Linhomoeidae</td><td>Linhomoeus</td><td>Linhomoeus sp1</td></tr><tr><td>Linhomoeidae</td><td>Linhomoeus</td><td>Linhomoeus sp2</td></tr><tr><td>Xyalidae</td><td>Linhystera</td><td>Linhystera sp1</td></tr><tr><td>Cyatholaimidae</td><td>Longicyatholaimus</td><td>Longicyatholaimus sp1</td></tr><tr><td>Desmodoridae</td><td>Molgolaimus</td><td>Molgolaimus sp1</td></tr><tr><td>Cyatholaimidae</td><td>Marylynnia</td><td>Marylynnia sp1</td></tr><tr><td>Linhomoeidae</td><td>Megadesmolaimus</td><td>Megadesmolaimus sp1</td></tr><tr><td>Desmodoridae</td><td>Metachromadora</td><td>Metachromadora sp1</td></tr><tr><td>Cyatholaimidae</td><td>Metacyatholaimus</td><td>Metacyatholaimus sp1</td></tr><tr><td>Xyalidae</td><td>Metadesmolaimus</td><td>Metadesmolaimus sp1</td></tr><tr><td>Linhomoeidae</td><td>Metalinhomoeus spp.</td><td>Metalinhomoeus spp.</td></tr><tr><td>Linhomoeidae</td><td>Metalinhomoeus</td><td>Metalinhomoeus sp1</td></tr><tr><td>Linhomoeidae</td><td>Metalinhomoeus</td><td>Metalinhomoeus sp2</td></tr><tr><td>Linhomoeidae</td><td>Metalinhomoeus</td><td>Metalinhomoeus sp3</td></tr><tr><td>Sphaerolaimidae</td><td>Metasphaerolaimus</td><td>Metasphaerolaimus sp1</td></tr><tr><td>Xyalidae</td><td>Manganonema</td><td>Manganonema sp1</td></tr><tr><td>Monhysteridae</td><td>Monhysteridae spp.</td><td>Monhysteridae spp.</td></tr><tr><td>Oxystominidae</td><td>Nemanema</td><td>Nemanema sp1</td></tr><tr><td>Chromadoridae</td><td>Neochromadora</td><td>Neochromadora sp1</td></tr><tr><td>Oncholaimidae spp.</td><td>Oncholaimidae spp.</td><td>Oncholaimidae spp.</td></tr><tr><td>Oncholaimidae</td><td>Oncholaimus</td><td>Oncholaimus sp1</td></tr><tr><td>Cyatholaimidae</td><td>Paracyatholaimus</td><td>Paracyatholaimus sp1</td></tr><tr><td>Comesomatidae</td><td>Paracomesoma</td><td>Paracomesoma sp1</td></tr><tr><td>Linhomoeidae</td><td>Paralinhomoeus</td><td>Paralinhomoeus sp1</td></tr><tr><td>Cyatholaimidae</td><td>Cyatholaimidae</td><td>Cyatholaimidae</td></tr><tr><td>Cyatholaimidae</td><td>Paralongicyatholaimus</td><td>Paralongicyatholaimus sp1</td></tr><tr><td>Enchelidiidae</td><td>Pareurystomina</td><td>Pareurystomina sp1</td></tr><tr><td>Axonolaimidae</td><td>Parodontophora</td><td>Parodontophora sp1</td></tr><tr><td>Desmodoridae</td><td>Perspiria</td><td>Perspiria sp1</td></tr><tr><td>Comesomatidae</td><td>Pierrickia</td><td>Pierrickia sp1</td></tr><tr><td>Chromadoridae</td><td>Prochromadorella</td><td>Prochromadorella sp1</td></tr><tr><td>Chromadoridae</td><td>Prochromadorella</td><td>Prochromadorella sp2</td></tr><tr><td>Xyalidae</td><td>Promonhystera</td><td>Promonhystera sp1</td></tr><tr><td>Oncholaimidae</td><td>Prooncholaimus</td><td>Prooncholaimus sp1</td></tr><tr><td>Chromadoridae</td><td>Ptycholaimellus</td><td>Ptycholaimellus sp1</td></tr><tr><td>Desmoscolecidae</td><td>Quadricoma</td><td>Quadricoma sp1</td></tr><tr><td>Comesomatidae</td><td>Sabatieria</td><td>Sabatieria sp1</td></tr></tbody></table>
<table><caption>Table S4. – Nematode diversity indices in the maerl bed: species richness (SR), Margalef diversity (D), Pielou evenness (J'), expected genus number (EG(51)) and Shannon index (H').</caption><thead><tr><th>Family</th><th>Genus</th><th>Species</th></tr></thead><tbody><tr><td>Comesomatidae</td><td>Setosabatieria</td><td>Setosabatieria sp1</td></tr><tr><td>Sphaerolaimidae</td><td>Sphaerolaimus</td><td>Sphaerolaimus sp1</td></tr><tr><td>Chromadoridae</td><td>Spiliphera</td><td>Spiliphera sp1</td></tr><tr><td>Chromadoridae</td><td>Spilophorella spp.</td><td>Spilophorella spp.</td></tr><tr><td>Chromadoridae</td><td>Spilophorella</td><td>Spilophorella sp1</td></tr><tr><td>Chromadoridae</td><td>Spilophorella</td><td>Spilophorella sp2</td></tr><tr><td>Desmodoridae</td><td>Spirinia</td><td>Spirinia sp1</td></tr><tr><td>Chromadoridae</td><td>Steineridora</td><td>Steineridora sp1</td></tr><tr><td>Chromadoridae</td><td>Steineridora</td><td>Steineridora sp2</td></tr><tr><td>Desmodoridae</td><td>Stilbonematinae</td><td>Stilbonematinae</td></tr><tr><td>Xyalidae</td><td>Stylotheristus</td><td>Stylotheristus sp1</td></tr><tr><td>Desmodoridae</td><td>Stygodesmodora</td><td>Stygodesmodora sp1</td></tr><tr><td>Selachinematidae</td><td>Synonchiella</td><td>Synonchiella sp1</td></tr><tr><td>Ironidae</td><td>Syringolaimus</td><td>Syringolaimus sp1</td></tr><tr><td>Linhomoeidae</td><td>Terschellingia spp.</td><td>Terschellingia spp.</td></tr><tr><td>Linhomoeidae</td><td>Terschellingia</td><td>Terschellingia sp1</td></tr><tr><td>Linhomoeidae</td><td>Terschellingia</td><td>Terschellingia sp2 (cf. longicaudata)</td></tr><tr><td>Monhysteridae</td><td>Thalassomonhystera</td><td>Thalassomonhystera sp1</td></tr><tr><td>Xyalidae</td><td>Theristus</td><td>Theristus sp1</td></tr><tr><td>Thoracostomopsidae</td><td>Thoracostomopsis</td><td>Thoracostomopsis sp1</td></tr><tr><td>Xyalidae</td><td>Trichoteristus</td><td>Trichoteristus sp1</td></tr><tr><td>Desmoscolecidae</td><td>Tricoma</td><td>Tricoma sp1</td></tr><tr><td>Thoracostomopsidae</td><td>Trileptium</td><td>Trileptium sp1</td></tr><tr><td>Oncholaimidae</td><td>Viscosia</td><td>Viscosia sp1</td></tr><tr><td>Oxystominidae</td><td>Wieseria</td><td>Wieseria sp1</td></tr><tr><td>Xyalidae spp.</td><td>Xyalidae spp.</td><td>Xyalidae spp.</td></tr></tbody></table>

<table><thead><tr><th>Layers</th><th>SR</th><th>D</th><th>J'</th><th>EG(51)</th><th>H'</th></tr></thead><tbody><tr><td>ML</td><td>19.0±4.4</td><td>4.8±1.2</td><td>0.9±0.0</td><td>19.0±4.4</td><td>2.7±0.3</td></tr><tr><td>0-1 cm</td><td>31.7±6.0</td><td>6.6±1.4</td><td>0.7±0.1</td><td>20.5±4.9</td><td>2.5±0.6</td></tr><tr><td>1-2 cm</td><td>24.7±6.0</td><td>4.9±1.3</td><td>0.7±0.0</td><td>16.0±4.2</td><td>2.3±0.3</td></tr><tr><td>2-3 cm</td><td>26.3±1.5</td><td>5.2±0.3</td><td>0.7±0.0</td><td>16.6±0.8</td><td>2.4±0.2</td></tr><tr><td>3-4 cm</td><td>22.0±1.4</td><td>4.4±0.1</td><td>0.8±0.0</td><td>15.2±0.5</td><td>2.4±0.1</td></tr></tbody></table>
<table><caption>Table S5. SIMPER analysis showing the contribution of nematode species to between-layer dissimilarity. The ten most contributing taxa are reported. The following abbreviations were used: Contrib.%, contribution%; Cum.%, cumulative %.</caption><thead><tr><th colspan="3">Groups ML & 0-1 cm</th><th colspan="3">Groups ML & 1-2 cm</th><th colspan="3">Groups ML & 2-3 cm</th></tr><tr><th>Species</th><th>Contrib%</th><th>Cum.%</th><th>Species</th><th>Contrib%</th><th>Cum.%</th><th>Species</th><th>Contrib%</th><th>Cum.%</th></tr></thead><tbody><tr><td>Terschellingia sp1</td><td>3.59</td><td>3.59</td><td>Spirinia sp1</td><td>5.16</td><td>5.16</td><td>Terschellingia sp2 (cf. longicaudata)</td><td>5.25</td><td>5.25</td></tr><tr><td>Molgolaimus sp1</td><td>2.89</td><td>6.48</td><td>Terschellingia sp2 (cf. longicaudata)</td><td>4.1</td><td>9.26</td><td>Spirinia sp1</td><td>4.21</td><td>9.46</td></tr><tr><td>Metalinhomoeus sp1</td><td>2.71</td><td>9.18</td><td>Terschellingia sp1</td><td>3.3</td><td>12.56</td><td>Sabatieria sp1</td><td>4.13</td><td>13.6</td></tr><tr><td>Sphaerolaimus sp1</td><td>2.63</td><td>11.81</td><td>Halichoanolaimus sp1</td><td>3.26</td><td>15.82</td><td>Terschellingia spp</td><td>3.1</td><td>16.69</td></tr><tr><td>Spirinia sp1</td><td>2.51</td><td>14.32</td><td>Metalinhomoeus sp1</td><td>3.21</td><td>19.03</td><td>Halaphanolaimus sp1</td><td>2.51</td><td>19.2</td></tr><tr><td>Halalaimus sp1</td><td>2.42</td><td>16.74</td><td>Parodontophora sp1</td><td>2.87</td><td>21.9</td><td>Steineridora sp1</td><td>2.35</td><td>21.55</td></tr><tr><td>Xyalidae</td><td>2.34</td><td>19.08</td><td>Sabatieria sp1</td><td>2.78</td><td>24.68</td><td>Perspiria sp1</td><td>2.22</td><td>23.77</td></tr><tr><td>Parodontophora sp1</td><td>2.33</td><td>21.4</td><td>Linhomoeus sp2</td><td>2.53</td><td>27.21</td><td>Linhomoeus sp2</td><td>2.21</td><td>25.98</td></tr><tr><td>Chromadorella sp1</td><td>2.30</td><td>23.7</td><td>Xyalidae spp.</td><td>2.26</td><td>29.47</td><td>Chromadorella sp1</td><td>2.17</td><td>28.15</td></tr><tr><td>Metalinhomoeus spp</td><td>2.13</td><td>25.83</td><td>Chromadorella sp1</td><td>2.2</td><td>31.67</td><td>Spilophorella sp1</td><td>2.17</td><td>30.32</td></tr></tbody></table><table><thead><tr><th colspan="3">Groups ML & 3-4 cm</th><th colspan="3">Groups 0-1 & 1-2 cm</th><th colspan="3">Groups 0-1 & 2-3 cm</th></tr><tr><th>Species</th><th>Contrib%</th><th>Cum.%</th><th>Species</th><th>Contrib%</th><th>Cum.%</th><th>Species</th><th>Contrib%</th><th>Cum.%</th></tr></thead><tbody><tr><td>Terschellingia sp2 (cf. longicaudata)</td><td>5.53</td><td>5.53</td><td>Terschellingia sp2 (cf. longicaudata)</td><td>3.01</td><td>9.83</td><td>Terschellingia sp2 (cf. longicaudata)</td><td>3.86</td><td>3.86</td></tr><tr><td>Metalinhomoeus spp</td><td>4.3</td><td>9.84</td><td>Pierrickia sp1</td><td>3.16</td><td>6.82</td><td>Molgolaimus sp1</td><td>3.68</td><td>7.54</td></tr><tr><td>Perspiria sp1</td><td>3.52</td><td>13.36</td><td>Spirinia sp1</td><td>3.66</td><td>3.66</td><td>Steineridora sp1</td><td>2.86</td><td>10.4</td></tr><tr><td>Halichoanolaimus sp1</td><td>3.51</td><td>16.87</td><td>Metalinhomoeus sp2</td><td>2.46</td><td>12.29</td><td>Diodontolaimus sp1</td><td>2.46</td><td>12.86</td></tr><tr><td>Metalinhomoeus sp1</td><td>3.36</td><td>20.23</td><td>Steineridora sp1</td><td>2.34</td><td>14.63</td><td>Perspiria sp1</td><td>2.45</td><td>15.31</td></tr><tr><td>Linhomoeus sp2</td><td>3.27</td><td>23.5</td><td>Daptonema sp1</td><td>2.34</td><td>16.96</td><td>Spirinia sp1</td><td>2.37</td><td>17.69</td></tr><tr><td>Sabatieria sp1</td><td>3.27</td><td>26.77</td><td>Linhomoeus sp2</td><td>2.16</td><td>19.13</td><td>Metalinhomoeus sp2</td><td>2.3</td><td>19.98</td></tr><tr><td>Spirinia sp1</td><td>3.27</td><td>30.04</td><td>Sphaerolaimus sp1</td><td>2.11</td><td>21.24</td><td>Sabatieria sp1</td><td>2.18</td><td>22.16</td></tr><tr><td>Metalinhomoeus sp2</td><td>3.01</td><td>33.06</td><td>Chromadora sp1</td><td>2.07</td><td>23.31</td><td>Daptonema sp1</td><td>2.08</td><td>24.24</td></tr><tr><td>Terschellingia sp1</td><td>2.61</td><td>35.66</td><td>Monhysteridae spp.</td><td>2.06</td><td>25.38</td><td>Leptolaimus sp1</td><td>2.04</td><td>26.28</td></tr></tbody></table><table><thead><tr><th colspan="3">Groups 0-1 & 3-4 cm</th><th colspan="3">Groups 1-2 & 2-3 cm</th><th colspan="3">Groups 1-2 & 3-4 cm</th></tr><tr><th>Species</th><th>Contrib%</th><th>Cum.%</th><th>Species</th><th>Contrib%</th><th>Cum.%</th><th>Species</th><th>Contrib%</th><th>Cum.%</th></tr></thead><tbody><tr><td>Perspiria sp1</td><td>4.28</td><td>4.28</td><td>Molgolaimus sp1</td><td>3.17</td><td>3.17</td><td>Perspiria sp1</td><td>6</td><td>6</td></tr><tr><td>Terschellingia sp2 (cf. longicaudata)</td><td>3.98</td><td>8.26</td><td>Halichoanolaimus sp1</td><td>3.03</td><td>6.21</td><td>Theristus sp1</td><td>3.55</td><td>9.54</td></tr><tr><td>Molgolaimus sp1</td><td>3.54</td><td>11.8</td><td>Marylynnia sp1</td><td>3.03</td><td>9.23</td><td>Molgolaimus sp1</td><td>3.37</td><td>12.91</td></tr><tr><td>Metalinhomoeus sp2</td><td>3.47</td><td>15.26</td><td>Perspiria sp1</td><td>3.02</td><td>12.25</td><td>Metalinhomoeus sp2</td><td>3.12</td><td>16.04</td></tr><tr><td>Halalaimus sp1</td><td>3.11</td><td>18.38</td><td>Halaphanolaimus sp1</td><td>2.87</td><td>15.12</td><td>Metalinhomoeus spp</td><td>3.05</td><td>19.09</td></tr><tr><td>Steineridora sp1</td><td>2.94</td><td>21.32</td><td>Metalinhomoeus sp1</td><td>2.56</td><td>17.68</td><td>Terschellingia spp</td><td>2.87</td><td>21.96</td></tr><tr><td>Pierrickia sp1</td><td>2.85</td><td>24.17</td><td>Metalinhomoeus spp</td><td>2.38</td><td>20.06</td><td>Spirinia sp1</td><td>2.79</td><td>24.75</td></tr><tr><td>Sphaerolaimus sp1</td><td>2.53</td><td>26.69</td><td>Linhomoeus sp1</td><td>2.35</td><td>22.4</td><td>Linhomoeus sp1</td><td>2.7</td><td>27.45</td></tr><tr><td>Linhomoeus sp2</td><td>2.32</td><td>29.01</td><td>Leptolaimus sp1</td><td>2.35</td><td>24.75</td><td>Halalaimus sp1</td><td>2.48</td><td>29.93</td></tr><tr><td>Daptonema sp1</td><td>2.3</td><td>31.31</td><td>Metalinhomoeus sp2</td><td>2.3</td><td>27.05</td><td>Leptolaimus sp1</td><td>2.41</td><td>32.34</td></tr></tbody></table><table><thead><tr><th colspan="3">Groups 2-3 & 3-4 cm</th></tr><tr><th>Species</th><th>Contrib%</th><th>Cum.%</th></tr></thead><tbody><tr><td>Metalinhomoeus spp</td><td>3.76</td><td>3.76</td></tr><tr><td>Halichoanolaimus sp1</td><td>3.35</td><td>7.11</td></tr><tr><td>Diodontolaimus sp1</td><td>3.28</td><td>10.38</td></tr><tr><td>Theristus sp1</td><td>3.28</td><td>13.66</td></tr><tr><td>Leptolaimus sp1</td><td>3.14</td><td>16.8</td></tr><tr><td>Perspiria sp1</td><td>3.08</td><td>19.87</td></tr><tr><td>Terschellingia spp</td><td>2.7</td><td>22.58</td></tr><tr><td>Metalinhomoeus sp2</td><td>2.68</td><td>25.25</td></tr><tr><td>Halalaimus sp1</td><td>2.62</td><td>27.87</td></tr><tr><td>Chromadoridae spp.</td><td>2.54</td><td>30.42</td></tr></tbody></table>
<table><caption>Table S6. – Meiofaunal abundance, number of higher taxa, nematode biomass, diversity (Shannon index (H'), equitability evenness (J'), expected genus number (EG(51)) and trophic diversity index (ITD)). List of exclusive and shared genera of nematodes between the maerl bed and the sandy beach.</caption><thead><tr><th></th><th>Maerl bed</th><th>Sandy beach</th><th>Maerl/ Sandy beach</th></tr></thead><tbody><tr><td>Meiofaunal abundance (ind/10 cm²)</td><td>1986±457</td><td>384±16</td><td></td></tr><tr><td>N° taxa</td><td>12</td><td>8</td><td></td></tr><tr><td>Nematode biomass (µgC/10 cm²)</td><td>108.2±41.9</td><td>47.6±2.1</td><td></td></tr><tr><td>H' (loge)</td><td>2.5</td><td>2.2</td><td></td></tr><tr><td>J'</td><td>0.8</td><td>0.7</td><td></td></tr><tr><td>EG(51)</td><td>18</td><td>15</td><td></td></tr><tr><td>ITD</td><td>0.3</td><td>0.6</td><td></td></tr><tr><td>Genera of nematodes</td><td>Acantholaimus<br>Actinonema<br>Antomicron<br>Campylaimus<br>Cephalanticoma<br>Chromadora<br>Chromadorella<br>Chromadorita<br>Cobbia<br>Comesomoides<br>Cyartonema<br>Cyatholaimidae<br>Desmoscolex<br>Diodontolaimus<br>Dorylaimopsis<br>Draconema<br>Euchromadora<br>Eumorpholaimus<br>Eurystomina<br>Filoncholaimus<br>Eurystomina<br>Filoncholaimus<br>Halalaimus<br>Halaphanolaimus<br>Halichoanolaimus<br>Halomonhystera<br>Karkinochromadora<br>Kraspedonema<br>Laimella<br>Leptolaimus<br>Linhomoeus<br>Linhystera<br>Longicyatholaimus<br>Marylynnia<br>Megadesmolaimus<br>Metachromadora</td><td>Chaetonema<br>Dasynemoides<br>Desmodora<br>Gonionchus<br>Microlaimus<br>Omicronema<br>Richtersia<br>Xyala</td><td>Comesoma<br>Daptonema<br>Molgolaimus<br>Neochromadora<br>Paracomesoma<br>Parodontophora<br>Promonhystera<br>Spirinia<br>Stylotheristus<br>Trichotheristus<br>Trileptium<br>Viscosia</td><td></td></tr></tbody></table>
<table><thead><tr><th>Maerl bed</th><th>Sandy beach</th><th>Maerl/ Sandy beach</th></tr></thead><tbody><tr><td>Metacyatholaimus</td><td></td><td></td></tr><tr><td>Metadesmolaimus</td><td></td><td></td></tr><tr><td>Metalinhomoeus</td><td></td><td></td></tr><tr><td>Metasphaerolaimus</td><td></td><td></td></tr><tr><td>Nemanema</td><td></td><td></td></tr><tr><td>Oncholaimus</td><td></td><td></td></tr><tr><td>Paracyatholaimus</td><td></td><td></td></tr><tr><td>Paralinhomoeus</td><td></td><td></td></tr><tr><td>Paralongicyatholaimus</td><td></td><td></td></tr><tr><td>Pareurystomina</td><td></td><td></td></tr><tr><td>Perspiria</td><td></td><td></td></tr><tr><td>Pierrickia</td><td></td><td></td></tr><tr><td>Prochromadorella</td><td></td><td></td></tr><tr><td>Prooncholaimus</td><td></td><td></td></tr><tr><td>Ptycholaimellus</td><td></td><td></td></tr><tr><td>Quadricoma</td><td></td><td></td></tr><tr><td>Sabatieria</td><td></td><td></td></tr><tr><td>Setosabatieria</td><td></td><td></td></tr><tr><td>Sphaerolaimus</td><td></td><td></td></tr><tr><td>Spiliphera</td><td></td><td></td></tr><tr><td>Spilophorella</td><td></td><td></td></tr><tr><td>Steineridora</td><td></td><td></td></tr><tr><td>Stilbonematinae</td><td></td><td></td></tr><tr><td>Stygodesmodora</td><td></td><td></td></tr><tr><td>Synonchiella</td><td></td><td></td></tr><tr><td>Syringolaimus</td><td></td><td></td></tr><tr><td>Terschellingia</td><td></td><td></td></tr><tr><td>Thalassomonhystera</td><td></td><td></td></tr><tr><td>Theristus</td><td></td><td></td></tr><tr><td>Thoracostomopsis</td><td></td><td></td></tr><tr><td>Tricoma</td><td></td><td></td></tr></tbody></table>