Lola De Cubber

Sébastien Lefebvre

Charline Fisseau

Vincent Cornille

Dr Sylvie Marylène Gaudron
email: sylvie.gaudron@upmc.fr

Linking life-history traits, spatial distribution and abundance of two species of lugworms to bait collection: a case study for sustainable management plan

Keywords: Arenicola marina, Arenicola defodiens, spawning, population structure, size at first maturity, recreational fisheries, conservation, English Channel

Arenicola spp. are marine benthic polychaetes dug for bait by anglers. Without regulation, this activity can lead to the decrease of lugworms' population meanwhile affecting the physical characteristics of the beach and the biodiversity. Here, we identified through morphology and genetics two species of lugworms, Arenicola marina and A. defodiens, within a Marine Protected Area of the Eastern English Channel (France). For each species, abundance and spatial distribution were assessed using a stratified random sampling and interpolation at four studied sites, as well as some life-history traits. These data were compared to lugworms' collection data to estimate its sustainability and to provide potential management measures. At one site, A. marina was present in large numbers on the higher and middle shore, whereas A. defodiens occupied the lower shore. At the other sites, both species co-occurred on the lower shore, and A. marina individuals were less numerous and lacking recruits. Spawning periods for A. marina occurred in early autumn and in late autumn for A.

defodiens. The size at first maturity of A. marina was at 3.8 cm of trunk length (between 1.5 and 2.5 years old). One site (Au) appeared in need for management when linking abundance data with bait collection, where harvest of both species represented ~14 % of the total amount of lugworms and was above the carrying capacity of the beach for A. marina. The retail value associated to lugworm harvesting within the MPA was estimated at the same level as the shrimp retail value. Our results highlight the need for some fishery regulations.

Introduction

Arenicola spp. (Annelida Polychaeta), are marine benthic coastal ecosystem engineers living in burrows on intertidal and subtidal soft-sediment beaches and estuaries from the Arctic to the Mediterranean [START_REF] Volkenborn | Ecosystem engineering in intertidal sand by the lugworm Arenicola marina[END_REF]. Two cryptic species of the genus Arenicola were recorded in the North Sea and the English Channel: A. marina (Linnaeus, 1758) and A.

defodiens [START_REF] Cadman | A new species of lugworm: Arenicola defodiens sp[END_REF]. They were formerly described as two varieties of the same species, A. marina being the "littoral" variety, and A. defodiens the "laminarian" variety [START_REF] Luttikhuizen | Pseudo-cryptic species Arenicola defodiens and Arenicola marina (Polychaeta: Arenicolidae) in Wadden Sea, North Sea and Skagerrak: Morphological and molecular variation[END_REF]. Indeed, A. marina rather occupies the higher shore to mid-shore in a U-shape gallery, between 10 to 40 cm below the sediment surface, while A.

defodiens is present on the lower shore to subtidal area in a deeper (up to 1-meter deep) and Jshape gallery [START_REF] Cadman | A new species of lugworm: Arenicola defodiens sp[END_REF][START_REF] Cadman | Distribution of two species of lugworm (Arenicola) (Annelida: Polychaeta) in South Wales[END_REF]. Only small morphological differences exist between the two species, the most notable being the annulations patterns of the first setigers and the shape of the gills [START_REF] Cadman | A new species of lugworm: Arenicola defodiens sp[END_REF]. Thus, their species discrimination was proven by genetics [START_REF] Cadman | Genetic evidence for two species of lugworm (Arenicola) in South Wales[END_REF]) and reconfirmed recently using COI and 16S gene markers [START_REF] Luttikhuizen | Pseudo-cryptic species Arenicola defodiens and Arenicola marina (Polychaeta: Arenicolidae) in Wadden Sea, North Sea and Skagerrak: Morphological and molecular variation[END_REF][START_REF] Pires | Expansion of lugworms towards southern European habitats and their identification using combined ecological, morphological and genetic approaches[END_REF]. Both species are dioecious and iteroparous [START_REF] Watson | Control of oocyte maturation, sperm activation and spawning in two lugworm species: Arenicola marina and Arenicola defodiens[END_REF] and their benthopelagic lifecycle (Farke and Berghuis, 1979a;[START_REF] Reise | Tidal flat ecology -An experimental approach to species interactions[END_REF], has only been described for A. marina. For this species, after the spawning event in early autumn, and before the recruitment in spring, young stages experience two successive dispersal phases, with a temporary settlement in between, where at a 'post-larval' stage the worm lives in a mucus tube attached to various substrates (sheltered soft-sediment, macroalgae or mussel beds) (Farke and Berghuis, 1979a,b;[START_REF] Reise | Tidal flat ecology -An experimental approach to species interactions[END_REF][START_REF] Reise | Density-dependent recruitment after winter disturbance on tidal flats by the lugworm Arenicola marina[END_REF].

Arenicola spp. play a key role in bioturbation of soft sediments [START_REF] Kristensen | Impact of polychaetes (Nereis spp. and Arenicola marina) on carbon biogeochemistry in coastal marine sediments[END_REF] and in local trophic networks [START_REF] Reise | Tidal flat ecology -An experimental approach to species interactions[END_REF][START_REF] Clarke | Intertidal invertebrate harvesting : a meta-analysis of impacts and recovery in an important waterbird prey resource[END_REF]. Moreover, despite lugworms are not considered yet as a fisheries species (as not directly consumed), they represent a high commercial marine value showing an important biomass extraction according to Watson et al. (2017a), who estimated a global landing for polychaete bait (including lugworms) up to 120 000 tonnes, representing ₤5.9 billion in 2016. Lugworm collection by professional or recreational fishermen may impact the size and age structure of a population, such as its abundance and distribution [START_REF] Blake | Exploitation of a natural population of Arenicola marina (L.) from the North-East Coast of England[END_REF][START_REF] Mclusky | Distribution and population recovery of Arenicola marina and other benthic fauna after bait digging[END_REF][START_REF] Olive | Management of the exploitation of the lugworm Arenicola marina and the ragworm Nereis virens (Polychaeta) in conservation areas[END_REF] with possible population crashes caused by overexploitation [START_REF] Olive | Management of the exploitation of the lugworm Arenicola marina and the ragworm Nereis virens (Polychaeta) in conservation areas[END_REF]. In addition, bait diggers can affect the physical characteristics of the beach perturbing the other associated fauna (invertebrates, wading birds, etc.) [START_REF] Beukema | Long-term effects of mechanical harvesting of lugworms Arenicola marina on the zoobenthic community of a tidal flat in the Wadden Sea[END_REF][START_REF] Clarke | Intertidal invertebrate harvesting : a meta-analysis of impacts and recovery in an important waterbird prey resource[END_REF]Watson et al., 2017b).

In consequence, several authors call for a management (Watson et al., 2017a), and particularly, a sustainable management of these species [START_REF] Clarke | Intertidal invertebrate harvesting : a meta-analysis of impacts and recovery in an important waterbird prey resource[END_REF].

Fisheries management can be defined as "the integrated process of information gathering, analysis, planning, consultation, decision-making, allocation of resources and formulation and implementation, with enforcement as necessary, of regulations or rules which govern fisheries activities in order to ensure the continued productivity of the resources and the accomplishment of other fisheries objectives" (FAO, 2002a). In other words, this consists in maintaining its population at healthy levels, which is, in terms of population's dynamics, a population with sustainable birth, growth and survival rates [START_REF] Beverton | On the dynamics of exploited fish populations[END_REF]. The management can be implemented through education, or through enforced harvest regulations [START_REF] Watson | Successful local marine conservation requires appropriate educational methods and adequate enforcement[END_REF]. The latter are in general applied either on the fishermen themselves, implementing licenses or fees, gear or fishing methods restrictions, closing times, season or area restrictions, either on the resource, limiting the length or quantity (bags) of the collected species mainly (FAO, 2012). Both controls are used to limit the overall mortality, or the mortality of specific individuals in the population, based on its features (FAO, 2012).

Several kinds of regulations for bait collection have already been enforced around the world, either for recreational or professional fishermen: licensing has been implemented in the United States and the United Kingdom [START_REF] Watson | Successful local marine conservation requires appropriate educational methods and adequate enforcement[END_REF], quotas have been implemented in Portugal [START_REF] Xenarios | Introducing a Regulatory Policy Framework of Bait Fishing in European Coastal Lagoons: The Case of Ria de Aveiro in Portugal[END_REF] and some areas have been closed in the UK [START_REF] Olive | Management of the exploitation of the lugworm Arenicola marina and the ragworm Nereis virens (Polychaeta) in conservation areas[END_REF][START_REF] Rogers | A review of closed areas in the United Kingdom Exclusive Economic Zone[END_REF]. For Arenicola spp. the last two options have already been implemented in some European places: a limitation to 100 individuals in a defined area in the North of France (Direction interrégionale de la mer Manche Est-mer du Nord, 2015) or the closure of areas where the lugworm population crashed in the UK [START_REF] Olive | Management of the exploitation of the lugworm Arenicola marina and the ragworm Nereis virens (Polychaeta) in conservation areas[END_REF][START_REF] Rogers | A review of closed areas in the United Kingdom Exclusive Economic Zone[END_REF]. Although protecting lugworms, the main purpose of these management methods is sometimes rather to protect the habitat features or the wading birds disturbed by fishermen (Watson et al., 2017b).

Besides, these management measures are merely restrictions, often taken without any considerations of the life history traits of the local populations (Watson et al., 2017a). Studies linking bait collection data to abundance, spatial distribution and life history traits of lugworm are scarce. [START_REF] Xenarios | Introducing a Regulatory Policy Framework of Bait Fishing in European Coastal Lagoons: The Case of Ria de Aveiro in Portugal[END_REF] assessed the sustainable levels of some polychaetes species (Diopatra neapolitana), only taking into account the harvest effort, and [START_REF] Blake | Exploitation of a natural population of Arenicola marina (L.) from the North-East Coast of England[END_REF] combined the harvest effort to population data (e.g. density and size structure). Nevertheless, the only study of this kind dealing with lugworms [START_REF] Blake | Exploitation of a natural population of Arenicola marina (L.) from the North-East Coast of England[END_REF] was performed before the knowledge of the co-occurrence of two potential species of the genus Arenicola inhabiting the intertidal area [START_REF] Cadman | Distribution of two species of lugworm (Arenicola) (Annelida: Polychaeta) in South Wales[END_REF].

In this study, we have assessed the abundance and the spatial distribution of several local populations of Arenicola spp. within a newly created MPA from temperate coastal areas located in the Eastern English Channel, as well as some life-history traits such as spawning period, size at first maturity, population structure and recruitment period. Additional data on lugworms' collection by recreational bait diggers within the MPA was included in order to estimate the potential sustainability of the different lugworms' population and to provide relevant potential management measures when needed.

Material and Methods

Study Area

The study area is located in the Eastern English Channel and is part of a marine protected area (MPA): the Parc naturel marin des estuaires picards et de la mer d'Opale created in 2012 (Fig. 1). The coastline is mainly composed of hydrodynamically exposed sandy beaches of fine to medium sands (0.05 to 0.5 mm grain size), as well as some rocky shores, and includes three major estuaries of muddy sands (2 to 3 % silt): the Somme, the Authie and the Canche estuaries [START_REF] Rolet | Map of the benthic communities of the sandy shores of the Eastern English Channel and the Southern Bight of the North Sea[END_REF][START_REF] Rolet | Linking macrobenthic communities structure and zonation patterns on sandy shores: Mapping tool toward management and conservation perspectives in Northern France[END_REF]. The tidal regime is semi-diurnal and macrotidal and, amplitude may exceed 8 m, with the largest amplitudes occurring around 2 days before the full moon [START_REF] Migné | In situ measurements of benthic primary production during emersion: seasonal variations and annual production in the Bay of Somme (eastern English Channel, France)[END_REF][START_REF] Rolet | Linking macrobenthic communities structure and zonation patterns on sandy shores: Mapping tool toward management and conservation perspectives in Northern France[END_REF]. Sampling sites (Fig. 1) were chosen at four locations along the shore of the MPA, where recreational fishermen had often been observed digging worms, in order to assess the need for management of this activity: 1) Wimereux (Wx) (50°46′14″ N and 1°36′38″ E), 2) Le Touquet (LT) (50°31′07″ N and 1°35′42″ E), 3) Fort Mahon (FM) (50°20′31″ N and 1°34′11″ E) and, 4) Ault (Au) (50°06′07″ N and 1°26′58″ E). LT and FM are composed of large exposed sandy beaches, when Wx and Au are a mixture of sandy beaches and rocky shores mainly colonized by algae and mussels on the intertidal and subtidal areas. 1.2. Spatial distribution and abundance of Arenicola spp.

Sampling strategy

Spatial distributions of lugworms were investigated on the sandy shore in April-Mai 2016 at the four sites (Wx, LT, FM and Au) during spring tide periods. Formerly, lugworms distributions were assessed by samplings on uniformly distributed points along transects [START_REF] Beukema | Population parameters of the lugworm Arenicola marina living on tidal flats in the Dutch Wadden Sea[END_REF][START_REF] Beukema | Long-term effects of mechanical harvesting of lugworms Arenicola marina on the zoobenthic community of a tidal flat in the Wadden Sea[END_REF]. However, on the studied sites, distributions of lugworms were highly aggregative (with spots of faecal casts and spaces without faecal casts next to them). Therefore, a stratified random sampling approach was chosen [START_REF] Fagan | Spatial sampling design in the circumpolar active layer monitoring programme[END_REF], in order to improve the performance of the spatial interpolation methods [START_REF] Li | A review of spatial interpolation methods for environmental scientists[END_REF]. At each site, the area was subdivided into a grid of equally-sized rectangle boxes: a grid of 100 m x 50 m divided into 18 boxes at Wx and at Au, and, a grid of 100 m x 70 m divided into 24 boxes at LT and at FM (Fig. 1). In each box, a random sampling point was computed (Fig. 1), where the abundance of lugworms (both species combined) was assessed by counting the number of faecal casts in three quadrates placed randomly, of 0.0625 m² (when densities were higher than 10 faecal casts), or of 1 m² (when densities were lower than 10 faecal casts). Every 3 to 5 sampling points, lugworms were dug using either an Alvey bait pump (Decathlon ltd, extracting the worm by suction), a fork or a shovel, and the proportion of each species was calculated at the different bathymetries to correct the number of individuals belonging to each species.

Species identification

Species identification was determined morphologically by the observation of the annulations pattern on the second chaetigerous segment (two annulations for Arenicola defodiens and three for A. marina) [START_REF] Cadman | A new species of lugworm: Arenicola defodiens sp[END_REF]. Subsamples of tissue of each worm were kept in a solution of absolute ethanol at -20°C. The DNA of 3 random individuals of A.

marina and 3 random individuals of A. defodiens was then extracted using the NucleoSpin®Soil kit according to manufacturer's instruction (Macherey-Nagel), amplified and sequenced by Genoscreen ltd (Institute Pasteur de Lille, France) in order to confirm the presence of the two different species within the MPA. Fragments of the mitochondrial cytochrome oxidase I-encoding gene (COImt DNA) (~ 670 pb) were amplified using the universal primers: LCO 1490 (5'-GGTCAACAAATCATA AAG ATA TTG G-3') and HCO 2198 (5'-TAAACT TCA GGG TGA CCA AAA AAT CA-3') [START_REF] Folmer | DNA primers for amplification of mitochondrial cytochrome c oxidase subunit I from diverse metazoan invertebrates[END_REF].

Polymerase Chain Reaction (PCR) was performed according to [START_REF] Pires | Expansion of lugworms towards southern European habitats and their identification using combined ecological, morphological and genetic approaches[END_REF]: an initial denaturing step of 3 min at 94°C, followed by 34 cycles at 94°C for 1 min, 45°C for 30s for hybridization, then 2 min at 72°C, and a final extension for 5 min at 72°C. COI sequences were manually checked using bioedit Ver. 7.0.0. [START_REF] Hall | BioEdit: a user-friendly biological sequence alignment editor and analysis program for Windows 95/98/NT[END_REF]. Each COI sequence was then deposited in GenBanK (Supplementary Material: Table A) and aligned with other COI sequences of A. marina and A. defodiens (retrieved from GenBank), as described by [START_REF] Pires | Expansion of lugworms towards southern European habitats and their identification using combined ecological, morphological and genetic approaches[END_REF]. This multiple alignment of COI sequences was exported to the software MEGA v7 [START_REF] Kumar | MEGA7: Molecular Evolutionary Genetics Analysis Version 7.0 for Bigger Datasets[END_REF] using ClustalW, in order to construct a molecular phylogenetic tree analysis based on the maximum likelihood method (Supplementary Material: Fig. B).

Data analyses

To assess the spatial distribution and abundance of Arenicola spp., first, the total number of lugworms at each point was estimated by the number of faecal casts (Farke et al., 1979), assuming that one worm produced 0.84 cast.tide -1 in A. marina (Supplementary Material: Fig.

C

). We assumed that both species produce approximately the same amount of casts per tide.

The relative proportions of A. marina and A. defodiens were recorded for each collection point taking into account the bathymetry (height above chart datum). Since only few individuals could be collected in spring 2016, the data from autumn and winter 2015 was also used (Table 1). Bathymetries were obtained from the interregional project "CLAREC, INSU -CNRS M2C-UNICAEN" (http://www.unicaen.fr/dataclarec/home/elevations.html). When no bathymetry record was available (FM), we used the distance from the shoreline as a proxy.

The shoreline HISTOLITT® was taken from the SHOM, the hydrographic and oceanographic service of the French navy (http://diffusion.shom.fr/loisirs/trait-de-cote-histolittr.html). The existence of a correlation between the proportions of the two species and the bathymetry or the shoreline distance was investigated (Spearman correlation test) at each site separately.

When a correlation between the proportion of A. marina and A. defodiens and bathymetry could be established (Wx), a fitting model was adjusted on Matlab R2015b using the Curve Fitting Toolbox and a sigmoid model inspired by [START_REF] Cadman | Distribution of two species of lugworm (Arenicola) (Annelida: Polychaeta) in South Wales[END_REF] (Supplementary Material: Spring 2016, which is based on species identification of the macrofauna and on the particle size analysis (Supplementary Material: Table F). The number of individuals of each species was obtained on the whole grid from the interpolation and then reduced to 1 m² to get the mean density. The significance of the difference of densities between sites was then estimated with a chi-squared test for each species separately, performed on R (R Core Team, 2017). 1.3. Life-history traits of the lugworm populations 1.3.1. Sampling strategy Spawning dates of both species were investigated for two successive breeding seasons, from September 2015 to January 2016 and from September 2016 to January 2017, at the four studied sites. Individuals were dug with a bait pump monthly on the lower shore or with a fork on the mid-shore, at low tide (Table 1). The population structure of Arenicola marina was investigated only at Wx (Fig. 1) within the intertidal area at three locations from the low/middle shore to the higher shore (0 m of bathymetry: 50°46'0.1" N and 1°36'20.3" E, 0.9 m of bathymetry (above 0 m): 50°46'1.7" N and 1°36'14.4" E and, 2.3 m of bathymetry (above 0 m): 50°46'2.5" N and 1°36'10.6" E) in July 2017. During low tide, 30 individuals from each location were collected by digging the sediment (between 5 and 30 cm beneath the surface), either with a pump, or a fork or by sieving (0.5 mm mesh) the sediment on the higher shore for the smaller individuals. This sampling strategy was repeated in September 2017 to assess the size at first maturity of A. marina at Wx.

Laboratory measurements

After each sampling, all worms were put in separated containers filled with seawater. Worms were maintained in the laboratory during 24 h to 48 h at 15°C in a cold room to allow gut contents to devoid prior to observations [START_REF] Watson | Can synchronous spawning be predicted from environmental parameters? A case study of the lugworm Arenicola marina[END_REF]. After identification, worms were anesthetized in three successive solutions of twice-filtered sea water (TFSW, 0.45 µm and 0.2 µm) at 1%, 2.5% and 5% of ethanol [START_REF] Gaudron | Control of reproductive behaviour in the scale worm Harmothoe imbricata[END_REF]. Each individual was measured (total length and trunk length) and weighted (wet weight). To assess their reproductive status, biopsies of the coelomic fluid were performed on individuals of Arenicola marina and A. defodiens (Table 1) with a sterile hypodermic syringe. The gametes were then rinsed twice in TFSW and kept in ethanol (96%) at 4°C. Fifty random oocytes of each female were measured under the microscope assisted by the software Motic Image Plus 2.0.

Reproductive structures of males (rosettes, morulae and spermatozoids) were analyzed using the same method. To assess the size at first maturity, the occurrence of gametes was searched in coelomic fluids of 106 individuals of A. marina.

Data Analysis Spawning dates

Spawning periods of both species were inferred by using both the oocyte diameter frequency distributions [START_REF] Watson | Control of oocyte maturation, sperm activation and spawning in two lugworm species: Arenicola marina and Arenicola defodiens[END_REF] and the presence of male gamete structures such as spermatozoids or morulae, only present in mature individuals [START_REF] Dillon | Contrasting breeding periodicity of nearby populations of the lugworm, Arenicola marina (Annelida, Polychaeta)[END_REF].

Furthermore, observation of spontaneous spawning events in the laboratory was considered as additional evidence that lugworms were at a maturity stage and ready to release gametes.

Population and age structures of Arenicola marina

In Arenicola spp., no permanent structures with year marks have been found [START_REF] Beukema | Population parameters of the lugworm Arenicola marina living on tidal flats in the Dutch Wadden Sea[END_REF]) and the population structure can only be approached through the analysis of the different size of cohorts, since spawning and recruitment only happen once a year and each cohort belongs therefore to a separate year. Only the population and age structures of A.

marina at Wx were assessed through the analysis of size frequencies on the trunk length (TL) frequency distributions of 5-mm size class intervals, using a Bhattacharya analysis (N = 194) performed on the specific routine in FISAT II package (FAO, 2002b) according to [START_REF] Romano | Submarine canyons as the preferred habitat for wood-boring species of Xylophaga (Mollusca, Bivalvia)[END_REF]. To assess the goodness of the modal separation, separation indices (SI) were computed with values of SI > 2 being considered as successfully separated. Mean TLs, standard deviations and separation indices were calculated for each of the identified cohorts.

Significant differences in TL of A. marina were assessed using a one-way analysis of variance (ANOVA) and a post-hoc Tukey test on R (R Core Team, 2017) (RStudio Team, 2016).

Normality of residuals was assessed by the Shapiro test (p > 0.05), and homoscedasticity was tested by the Bartlett test (p > 0.05) on R (R Core Team, 2017).

First size and age at maturity of Arenicola marina

The first size at maturity is the size at which more than 50% of the individuals are 'mature' (i.e. able to produce gametes, thus adult stage). Since reproductive organs are difficult to observe in Arenicola spp. [START_REF] Cassier | La reproduction des invertébrés : stratégies, modalités et régulation : intérêt fondamental et appliqué[END_REF], the presence/absence of gametes in the coelomic fluid was checked at the end of the gametogenesis period (September). These observations allowed to estimate the number of individuals containing gametes (adults), and that without gametes (juveniles). The cumulated frequency of the proportion of 'mature' individuals per trunk length (TL) class was then calculated and the size at first maturity was considered the size at which the cumulated frequency equaled to 0.5 (or 50 %). The differences in TL between adult males and females of A. marina at Wx, and between adults and juveniles (at the same site) were assessed using a non-parametric Kruskal-Wallis (K-W) test as distributions were not normal (Shapiro test, p < 0.05, performed on R (R Core Team, At the four studied sites, the mean number of lugworms available for bait diggers was assessed from the mean densities of lugworms established in this study, the surface of the foreshore and the percentage of lugworms weighing more than 3 g (weight considered by [START_REF] Olive | Management of the exploitation of the lugworm Arenicola marina and the ragworm Nereis virens (Polychaeta) in conservation areas[END_REF] as the limit at which worms get valuable). Then, these data were compared to the estimated number of dug lugworms assessed by the survey. 2. Results

Species identification, spatial distribution and abundance

The 6 random individuals chosen for a molecular analysis based on the COI genes confirmed the morphological identification (barcoding) (Supplementary Material: Fig. B,Table A). A 14-15 % of nucleotide divergence was found between the COI genes of Arenicola marina and A. defodiens. At Wx, a significant correlation was found between the proportion of each species and bathymetry (Spearman, ρ = 0.9, p < 0.001) and a relation could be established (Supplementary Material: Fig. D). It appeared that A. marina was present above -1 m of bathymetry and A. defodiens below -2 m of bathymetry, with a small transition in between,

where the two species could live in sympatry. On the other studied sites, no correlation was found between the proportion of each species and bathymetry or distance from the shoreline (LT: Spearman, ρ = -0.09, p > 0.1; FM: Spearman, ρ = 0.25, p > 0.1) (Supplementary Material: Fig. E). At Wx, A. defodiens was found on the lower shore, on the A2.23 EUNIS habitat and A. marina was mainly present on the higher shore, on the A2.223 EUNIS habitat (Fig. 2; Supplementary Material: Table F). At LT and FM, both species appeared to live in sympatry. Lugworms at LT were present on the A2.23 EUNIS habitat and at FM, lugworms were found on the A5.231 EUNIS habitat (Fig. 2; Supplementary Material: Table F). At Au,

A. defodiens was found on the lower shore, on the A2.23 EUNIS habitat (Fig. 2; Supplementary Material: Table F), but no conclusions were made regarding the distribution of A. marina on this site since only a single individual was collected. The mean densities of A.

defodiens did not appear to vary significantly between sites (between 0.25 ± 0.05 and 0.70 ± 0.05 individuals. m -² at all sites) (CHI 2 , p = 0.96) in comparison with A. marina (6.5 ± 0.8 individuals. m -² at Wx, around 0.2 individuals. m -² at LT and FM), where it varied significantly (CHI 2 ; p < 0.01) (Fig. 2).

Life history traits of lugworms 2.2.1. Spawning dates

For both species, the frequency distribution of the oocytes diameters evolved from a bimodal distribution for females carrying oocytes in oogenesis, with one peak of small oocytes (< 50 µm) and one peak of larger oocytes (> 100 µm), to a unimodal distribution with one single peak of large oocytes (~ 150 µm for Arenicola defodiens and ~ 180 µm for A. marina) for females where oocytes have completed vitellogenesis and are ready to be released (example at Wx for A. defodiens on Fig. 3

Population structure and age

At Wx, individuals of Arenicola marina ranged from 0.3 to 9 cm TL. The size-frequency distribution was multimodal (5 modes, SI > 2) (Table 2, Fig. 4a), suggesting the presence of 5 different age groups, the first one being the recruits' group (0.90 ± 0.37 cm TL). Since no recruits were spotted in April-May 2016 but some were observed in July 2017, recruitment may happen at the end of spring and/or beginning of summer at Wx. TL means of the three groups of TL delimited by the high (2.3 m of bathymetry), medium (0.9 m of bathymetry) and low (0 m of bathymetry) levels on the shores were significantly different (ANOVA: F (1,2) = 67.16; p < 0.001; Post-hoc Tukey p < 0.001), which suggests that recruitment happens on the upper shore (Fig. 4b). Given the weight-size relationship found for A. marina at Wx (Fig. 4c), lugworms reached the weight of 3 g between 5 and 9 cm, which means not before reaching 3 years old. At Wx, 12.6 % of the sampled A. marina and 100 % of the sampled A. defodiens had a weight superior to 3 g. 100 % of the individuals of the two species were above 3 g at the other sites, except for A. marina at Au, where the only individual collected weighted 2.5 g.

First size at maturity of A. marina

Adult lugworms ranged from 2.5 to 6.3 cm (TL). The first size at maturity of Arenicola marina at Wx was assessed at 3.8 cm of TL (Fig. 5), which corresponds approximately to 1 g of wet weight (Fig. 4c). No significant difference was found between the lengths of males and females (K-W: 0.63, p > 0.05), then all the data were analysed together. A highly significant difference between the size of juveniles (2.29 ± 0.97 cm) and adults (3.92 ± 0.91 cm) was observed (K-W: 0.96, p < 0.001) (Fig. 5). According to the population structure of A. marina from Wx, lugworms become adult between 1.5 and 2.5 years-old (Fig. 4a, Table 2).

Bait collection data and retail value

Most of the data presented here is available at https://estamp.afbiodiversite.fr/donnees. In total, 3 638 on-site observations were made within the MPA between 2014 and 2016. Among them, 88 were performed at Wx, 54 at LT, 60 at FM and 61 at Au. At these sites, 27 fishermen's baskets were randomly selected in order to estimate the number of dug lugworms (10 at Wx, 5 at LT and 12 at FM). The number of recreational diggers was highly variable along the MPA's foreshore. Au was the site where more lugworms' diggers were spotted on the whole MPA, with less than 4 000 diggers recorded in 2015. On the other studied sites, the number of recreational diggers ranged from ~ 300 at FM, ~ 700 at LT to ~ 1 200 diggers at Wx (Table 3). The mean estimated catch per fishing session varied according to the studied site from ~ 21 lugworms at FM to ~ 40 lugworms at Wx (Table 3). Since no value was available at Au, we used the mean value of the three other studies sites giving ~31 lugworms per tide and per recreational fisherman (Table 3). The estimated number of dug lugworms at the studied sites ranged from ~ 6 000 lugworms at FM to more than ~ 110 000 Arenicola spp.

at Au which led to a retail value varying between ~ 3 000 € at FM to more than ~ 49 000 € at Au in 2015 (Table 3). The total retail value of recreational arenicolid fisheries within the MPA (232 447 €) appeared to be about the equivalent to the retail value of the recreational shrimp Crangon crangon fisheries (215 714 to 414 727 €), and only 4 to 5 times less important than the one of the recreational mussel Mytilus edulis fisheries (1 203 449 €) (Table 3).

Linking lugworms' life-history traits to bait collection data

At the four studied sites, the number of lugworms above 3 g (e.g. considered as valuable by fishermen [START_REF] Olive | Management of the exploitation of the lugworm Arenicola marina and the ragworm Nereis virens (Polychaeta) in conservation areas[END_REF]) ranged between ~ 700 000 Arenicola spp. at FM to ~ 1 300 000

Arenicola spp. at Wx (Table 3, Fig. 6). In 2015, the number of lugworms dug by recreational fishermen represented respectively 3.6 % of the number of lugworms (both species combined) greater than 3 g at Wx, 2.9 % at LT, 0.9 % at FM, and 13.9 % at Au, and respectively 0.8 % of the total number of lugworms (both species combined) at Wx, 2.9 % at LT, 0.9 % at FM, and 13.7 % at Au (Fig. 6). At Au only, the number of dug lugworms for the year 2015 (117 791 lugworms) was greater than the estimated abundance of A. marina (12 810 lugworms in total, all weights considered), only considering recreational fisheries (Fig. 6). 3. Discussion

Species identification, abundances and spatial distribution

Our results confirmed the occurrence of both Arenicola marina and A. defodiens on the French coast of the Eastern English Channel, only mentioned by [START_REF] Müller | Faune et flore du littoral du nord, du Pas-de-Calais et de la Belgique[END_REF] while other authors only reported A. marina in ecological studies (e.g. [START_REF] Rolet | Map of the benthic communities of the sandy shores of the Eastern English Channel and the Southern Bight of the North Sea[END_REF] and may have been confusing the two species, especially in sites where they live in sympatry on the same level of the shore (on the lower shore). However, since A. defodiens burrows deeper into the sand, it is therefore harder to collect and previous studies may have failed in collecting this latter species, for which only bait pumps proved to be efficient. Until now, A. defodiens has only been described in the UK, the Netherlands and Portugal (Atlantic Ocean). In this study, we have shown the evidence of the occurrence of A. defodiens on the French coast of the Eastern English Channel, suggesting that this species is widely distributed on the whole French coast of both the English Channel and the Atlantic Ocean.

The maximum abundance of Arenicola marina found in this study at Wx (61 individuals. m -²)

was comparable to those found in other studies in the Wadden Sea and Portugal (~ 40 to 70 individuals. m -² max) [START_REF] Beukema | Population parameters of the lugworm Arenicola marina living on tidal flats in the Dutch Wadden Sea[END_REF][START_REF] Flach | Density-governing mechanisms in populations of the lugworm Arenicola marina on tidal flats[END_REF][START_REF] Pires | Expansion of lugworms towards southern European habitats and their identification using combined ecological, morphological and genetic approaches[END_REF] but did not reach the highest abundance recorded by Farke et al. (1979) (more than 150 individuals. m -²). In comparison, the values found at LT and FM for this species (2.7 and 0.6 individuals. m -² max respectively) appeared relatively low. This discrepancy may be linked to physical disturbances within the higher shore at these two sites caused by mechanical engines that remove debris deposited by the tide. [START_REF] Beukema | Long-term effects of mechanical harvesting of lugworms Arenicola marina on the zoobenthic community of a tidal flat in the Wadden Sea[END_REF] showed that repeated mechanical harvest of lugworms using digging machines similar to what is present at LT and FM, could decrease the overall densities of worms. In these two sites no recruits were observed during the spring period and only few individuals were collected on the higher shore during the autumn. Some individuals of A. marina may have migrated on the lower shore, on the EUNIS habitat A2.23 (medium to fine sands with amphipods and Scolelepis sp.) or even on the EUNIS habitat A5.231 (medium to fine sands with Donax vittatus), as lugworms may do during cold winters [START_REF] Wolff | Biomass and production of zoobenthos in the Grevelingen estuary, the Netherlands[END_REF]. The trade-off made by sharing the same ecological niche with A. defodiens on the lower shore at FM and LT involves interspecific competition for food and habitat, higher predation rate by birds and flatfish. This would make the survival rate of A. marina lower, and consequently decrease its abundance in comparison with sites where A. marina could live not in sympatry with A. defodiens such as at Wx. For A.

defodiens, the maximum abundance at all sites ranged from 1.6 to 2.9 individuals. m -². This is between the end of spring and the beginning of summer, which mirrored recruitment period recorded by [START_REF] Flach | Density-governing mechanisms in populations of the lugworm Arenicola marina on tidal flats[END_REF]. No recruits of A. marina were detected on the other sites. Since sampling for spatial distribution pattern was performed at the beginning of spring at LT and FM, we might have come too early to detect recruitment of the first cohort of A.

marina on these sites and further investigation will be needed since some small individuals were then detected on the upper shore in autumn 2016 at both sites. However, another possible explanation to the uneven distribution and abundance of A. marina recorded at the different sites might be explained by a particularly low survival rate of the recruits at LT, FM, and Au compared to Wx, due to physical disturbance as mentioned earlier. Another hypothesis is linked to the lifecycle of A. marina that involves a post-larval nursery grounds composed of sheltered soft sediments, macro-algae and/or mussel beds (Farke and Berghuis, 1979b;[START_REF] Reise | Tidal flat ecology -An experimental approach to species interactions[END_REF]. These transitory colonization habitats might have been degraded by anthropogenic disturbance at Au [START_REF] Paute | La pêche à pied des moules et des crevettes sur le littoral du Cap Gris Nez au Tréport : effet des pratiques et suivi des ressources[END_REF] or naturally absent close to LT and FM (as suggested by the subtidal macrobenthic community map for the area designed by Croguennec et al. ( 2011)), enhancing a post-larval mortality and subsequently a low recruitment of juveniles on the beach after the second larval dispersal phase. The low recruitment of A.

marina at LT, FM and Au might also be linked again to the two phases of dispersal during its lifecycle, where, under certain weather conditions, a strong current may be directed up North [START_REF] Bailly Du Bois | Water masses circulation and residence time in the Celtic Sea and English Channel approaches, characterisation based on radionuclides labelling from industrial releases[END_REF][START_REF] Ellien | The influence of variability in larval dispersal on the dynamics of a marine metapopulation in the eastern Channel[END_REF][START_REF] Nicolle | Modelling larval dispersal of Pecten maximus in the English Channel: a tool for the spatial management of the stocks[END_REF] during the second dispersal phase prior to the settlement of juveniles on the higher shore, favoring recruitment to North sites such as Wx (which could be considered as a sink of propagules) compared to the three others sites that are more south on the MPA (which could rather be considered as sources of propagules). Further studies on larval dispersal using a modeling approach based on biophysical model or population genetics should be applied to support this hypothesis. 3.3. Linking life-history traits, abundance and spatial distribution to bait collection data: management stakes and fishery At Wx, LT and FM, according to the survey carried out in 2015 on recreational fishermen, extraction levels of lugworms appeared quite low compared to the lugworm abundances calculated in this study (less than 5% of the population harvested). Moreover, the presence of numerous young individuals of A. marina at Wx seems to ensure a rapid renewal of the part of the population allocated to bait digging. However, 104 professional licenses have been delivered to some fishermen specialized in lugworm digging within the MPA and some of them are able to extract more than 400 worms per tide (anonymous fisherman communication). The lugworm extraction may have been underestimated in this study as the survey was done only on recreational fishermen. Besides, the proportion of the lugworm population dug at Au was already quite high (13.7 % of the total number of individuals and 13.9 % of the individuals heavier than 3 g). If we consider that the maximum age of Arenicola defodiens is close to the one of A. marina, which is around 5 to 6 years old, it means that every year, around one sixth to one fifth (e.g. 17% to 20%) of the population is renewed [START_REF] Beukema | Population parameters of the lugworm Arenicola marina living on tidal flats in the Dutch Wadden Sea[END_REF]. In this case, maybe the managers of the MPA should consider following up the population's density of this species to make sure that its abundance does not decrease over time. If so, some preventive management measures should be implemented such as forbidding or restricting the bait collection during the spawning periods and giving a minimum size limit of worm collection. Again, the numbers of A. marina were really low at Au compared to the total number of dug individuals, and actions should be taken to follow up and manage this species in order to allow its recovery. The species was found to be able to produce gametes (adult) between the cohort 2 and 3 (1.5 to 2.5 years old and approximately 1 g) and managers should encourage local fishermen to harvest only lugworms from cohorts 4

or 5 (i.e. worms that spawned at least once, older than 3 years old), where worms are larger to 6.15 cm long (TL) and getting close to 3 g (Fig. 3c). Although, further study of the dynamics of population of this studied site is needed to determine the best "size limit" management strategy [START_REF] Gwinn | Rethinking length-based fisheries regulations: The value of protecting old and large fish with harvest slots[END_REF], especially since the weight/size/age relationships of A. marina

were only studied at Wx, where the growth of the individuals of this species might be different from the one of the individuals of the same species at Au. However, as mentioned before, Au might not be a sink of larvae of A. marina. A second hypothesis is due to the natural mussels' beds of this site that is not in a good status and may lead to a mortality of the first settlers during their lifecycle [START_REF] Reise | Tidal flat ecology -An experimental approach to species interactions[END_REF][START_REF] Paute | La pêche à pied des moules et des crevettes sur le littoral du Cap Gris Nez au Tréport : effet des pratiques et suivi des ressources[END_REF]. These last considerations enlighten the need for an integrated management of the different activities, species and habitats in the area.

The total retail value of recreational fisheries for Arenicola spp. within the MPA appeared to be about equivalent to the one of the shrimp Crangon crangon, and only 4 to 5 times less important than the one of the mussel Mytilus edulis (in terms of recreational fisheries). These last two species benefit within the MPA from a number of catch restrictions (length and bags limits, closing fishing areas, restrictions on catch engines, etc.) (Direction interrégionale de la mer Manche Est-mer du Nord, 2015), when no restriction exists for Arenicola spp.

recreational fisheries within the MPA.

In order to give restrictions, distinguishing the two species of lugworms will be necessary, and especially, when sympatry of the two species occurs. [START_REF] Pires | Expansion of lugworms towards southern European habitats and their identification using combined ecological, morphological and genetic approaches[END_REF] suggested that there could be a difference in the shape of the faecal casts, where the faecal casts of A.

defodiens are more spiral-like than those of A. marina. These features could be taught to anglers when fishing for one of the two species must be limited. If size limit of the bait will be needed, size of the cast diameter of the lugworms may be used as an indicator, as this has been well correlated with the size of the worm itself such as in A. marina [START_REF] Olive | Management of the exploitation of the lugworm Arenicola marina and the ragworm Nereis virens (Polychaeta) in conservation areas[END_REF] unpublished data). Again, this information could be communicated to fishermen through education [START_REF] Watson | Successful local marine conservation requires appropriate educational methods and adequate enforcement[END_REF].

To conclude, the management of the lugworm populations within the MPA and some fishery regulation appear crucial given their ecological and economical importance with some populations (e.g. Au) that may be threatened by human activities.

745 19 When boxes appear, darker the sites were not sampled at the corresponding date. and water temperatures (in green).

Fig

  Fig. D). The number of individuals of each species was then calculated following the fitted model at each collection point's bathymetry. When no particular correlation was noticed (LT, FM) (Supplementary Material: Fig. E), the number of individuals of each species was calculated from the overall proportion of the individuals of both species from autumn 2015 to spring 2016. Eventually, when the number of individuals of A. marina and A. defodiens was assessed in every point of the grid, it was then interpolated on QGis 2.18.0 (QGIS development team, 2016) using the inverse distance weight (IDW) method. Interpolations were superimposed to EUNIS habitat communities maps obtained from Rolet et al. (2014) and from additional samplings performed according to Rolet et al. (2014) at FM and Au in

  photoperiod, maximum wind strength and atmospheric pressure), the tidal conditions (tidal coefficient, tidal range and low tide time), and the availability of fishermen (French and Belgium holidays, working days, week-ends, period of the year, morning or afternoon). The mean number of diggers per category and per site and the associated standard deviation were calculated, as well as the number of occurrences of each category in one year, which gave the number of diggers per site for this category in one year, as well as for the whole MPA. The total number of diggers for each site and for the whole MPA was then calculated summing the results of each category. The lugworms' extraction levels were calculated multiplying the total number of fishing sessions per site by the mean number of worms dug out by one fisherman in one fishing session. Finally, the retail value for the whole MPA and for each of the four studied sites was assessed from the numbers of dug lugworms and from the local retail prices taken from websites and from local retailers as inWatson et al. (2017a).

Figure captions Figure 1 .

 captions1 Figure captions

Figure 2 .

 2 Figure 2. Spatial distributions of the two species Arenicola marina and A. defodiens at the four studied sites: Wimereux (Wx), Le Touquet (LT), Fort Mahon (FM) and Ault (Au), and associated bathymetries (height above chart datum) or distance from the shoreline and EUNIS habitats.

Figure 3 .

 3 Figure 3. Evolution of the oocyte diameter frequencies of Arenicola defodiens at Wimereux between October 2015 and January 2016, measured on 50 random oocytes of n individuals.

Figure 4 .

 4 Figure 4. Length-frequency distributions of the trunk lengths of all specimens of Arenicola marina obtained from Wimereux in summer 2017 analysed using FISAT II. Normal curves represent each detected cohort (C.1 to C.5) (A), spatial distribution of the different sizes along the shore level (low = 0.1 m of bathymetry, medium = 0.9 m of bathymetry and high = 2.3 m of bathymetry) (B) and associated length-weight relationship (C). Since recruitment happens once a year at the same period, each cohort represents an age group. Cohort C.1 comprises the newly recruits, born in autumn 2016, C.2 the 1.5 years old individuals, born in autumn 2015, etc.

Figure 5 .

 5 Figure 5. Sizes in juveniles and adults of Arenicola marina at Wimereux (A), relative proportion of adults per size class (B) and its associated cumulated frequency (C).

Figure 6 .

 6 Figure 6. Comparison of the total number of individuals, number of individuals above 3 g and number of lugworms harvested in 2015 by recreational fishermen respectively for Arenicola marina, A. defodiens, and both species combined at Wimereux (Wx), Le Touquet (LT), Fort Mahon (FM) and Ault (Au).

Figure B .

 B Figure B. Maximum Likelihood tree of COI sequences of arenicolid species with bootstrapping values. The specimens sequenced in this study are highlighted and acronyms are described in Table A.

Figure C .

 C Figure C. Linear relation between the number of faecal casts produced and the number of individuals of Arenicola marina.

Figure D .

 D Figure D. Proportion of Arenicola marina (red dots) and A. defodiens (blue dots) according to bathymetry at Wimereux and the associated fitting transition curves and functions, as well as the number of lugworms collected at each point to calculate the proportion (weight of the different proportion points).

Figure E .

 E Figure E. Proportion of Arenicola marina (red dots) and A. defodiens (blue dots) according to bathymetry or distance from the shoreline and the related number of individuals used to calculate the proportion at Le Touquet (LT) and Fort Mahon (FM).

Figure G. 1 .

 1 Figure G.1. Oocyte diameter distributions of the collected females of Arenicola marina (N is the number of females) at Fort Mahon and Le Touquet in autumn 2015. When boxes appear darker, the sites were not sampled at the corresponding date.

Figure G. 2 .

 2 Figure G.2. Oocyte diameter distributions of the collected females (N is the number of females) of Arenicola marina at Fort Mahon, Le Touquet and Wimereux in autumn 2016.

Figure G. 3 .

 3 Figure G.3. Oocyte diameter distributions of the collected females (N is the number of females) of Arenicola defodiens at all sites in autumn and winter 2015/2016. When boxes appear darker, the sites were not sampled at the corresponding date.

Figure G. 4 .

 4 Figure G.4. Oocyte diameter distributions of the collected females (N is the number of females) of Arenicola defodiens at Wimereux, Le Touquet and Fort Mahon in autumn and winter 2016/2017. When boxes appear darker, the sites were not sampled at the corresponding date.

Figure H .

 H Figure H. Inferred spawning dates of Arenicola marina (red) and A. defodiens (blue) at all sampled sites in 2015 (darker) and 2016 (lighter) and associated tide coefficients (in black)

Table 1 : Summary of the number of samples and the associated name of the collected species, date, site and type of EUNIS habitat for the 746 assessment of the biological traits of the two lugworm species at Wimereux (Wx), Le Touquet (LT), Fort Mahon (FM) and Ault (Au).

 1

	Biological traits	Site	Species*	Number of individuals (n)	Type of EUNIS habitat **	Date
	Population structure	Wx	Arenicola marina	186	A2.223	May and July 2017
		Wx	A. marina A. defodiens	24 5	A2.223 + A2.23 A2.223 + A2.23	March 2016
	Species distribution	LT FM	A. marina A. defodiens A. marina A. defodiens	4 1 4 3	A2.223 + A2.23 A2.223 + A2.23 A2.223 + A2.23 A2.223 + A2.23	April 2016 April 2016
		Au	A. marina A. defodiens	1 11	A2.23 A2.23	May and June 2016
			A. marina	51 86	A2.223	Sept -Nov 2015 Sept -Oct 2016
		Wx	A. defodiens	34 16	A2.23	Sept 2015 -Jan 2016 Oct 2016 -Dec 2016
	Spawning period	LT	A. marina A. defodiens	17 8 16 12	A2.23 + A2.223 A2.23	Oct -Dec 2015 Oct 2016 Nov 2016 Oct -Dec 2015
		FM	A. marina A. defodiens	5 19 17 11	A2.23 + A2.223 A2.23	Sept -Nov 2015 Oct 2016 Sept -Nov 2015 Nov 2016
		Au	A. defodiens	26	A2.23	Oct -Nov 2015
	Size at first maturity	Wx	A. marina	106	A2.223	Sept 2017
	747
	748

Table 2 : Mean size and number of individuals and separation indices (SI) of every cohort found with the Bhattacharya analysis Mean trunk length (cm) Number of individuals SI

 2

	Cohort 1	0.90 ± 0.37	27	-
	Cohort 2	2.56 ± 0.60	36	3.42
	Cohort 3	4.82 ± 0.55	76	3.93
	Cohort 4	6.15 ± 0.56	41	2.40
	Cohort 5	8.21 ± 0.46	14	4.04
	Total sample	4.12 ± 1.93	194	-

Table F .

 F EUNIS habitats found at Fort Mahon and Ault based on particle size analysis and 20 species identification at these sites

	Site	GPS location	Species abundancy (%)		Particle size analysis (%)	Corresponding EUNIS habitat
			Donax vittatus Urothoe poseidonis Nephtys cirrosa	73 mudstones 10 fine sands 8 medium sands	0 70.7 23.6	A5.231 Medium to fine sands with Donax vittatus
			Spio martinensis	5	coarse sands	1.9
			Urothoe brevicornis	5	fine gravels	1.8
			Notrotopis falcatus	4	coarse gravels	2.1
		1°32'31.68'' E 50°20'24.89'' N	Lanice conchilega (juveniles)	4
			Eurydice pulchra	3
			Vaunthompsonia cristata	2
			Gastrosaccus spinifer	1
			Spio sp.	1
			Nephtys hombergii	1
			Eteone picta	1
	Fort Mahon (FM)	1°32'39.03'' E	Nephtys cirrosa Eurydice pulchra Portumnus latipes	57 mudstones 21 fine sands 14 medium sands	0 53.1 43.6	A2.2313 Nephtys cirrosa dominated littoral fine sands
		50°20'24.36'' N	Nephtys hombergii	7	coarse sands	1.8
					fine gravels	1
					coarse gravels	0.5
		1°32'47.60'' E	Eurydice pulchra Scolelepis squamata Haustorius arenarius	60 mudstones 39 fine sands 0.3 medium sands	0 34.2 63.5	A2.2232 Eurydice pulchra in littoral mobile sand
		50°20'23.32'' N	Urothoe poseidonis	0.3 coarse sands	1.6
			Bathyporeia pilosa	0.3 fine gravels	0.5
			Nemertean	0.3 coarse gravels	0.2
		1°32'54.07'' E	Scolelepis squamata Bathyporeia pilosa Carcinus maenas	81 mudstones 13 fine sands 2 medium sands	0 35.4 62.1	A2.2231 Scolelepis spp. in littoral mobile sand
		50°20'22.79'' N	Ophelia rathkei	2	coarse sands	1.4
			Haustorius arenarius	2	fine gravels	0.3
					coarse gravels	0.7
		1°27'09.49'' E 50°06'43.13'' N	Nephtys cirrosa Bathyporeia pelagica Portumnus latipes	50 mudstones 19 fine sands 6 medium sands	0.1 58.0 38.3	A2.2313 Nephtys cirrosa dominated littoral fine sand
		and	Haustorius arenarius	6	coarse sands	1.9
	Ault (Au)	1°27'04.04'' E 50°06'44.05'' N 1°27'15.07'' E 50°06'42.31'' N	Nephtys hombergii Lanice conchilega Oligochaete Paraonis fulgens Gastrosaccus spinifer Eurydice pulchra Nephtys hombergii Bathyporeia pelagica	6 6 6 31 mudstones fine gravels coarse gravels 19 fine sands 19 medium sands 13 coarse sands 13 fine gravels	0.9 0.9 0.1 30.8 66.3 0.8 0.4	A2.2311 Polychaetes, including Paraonis fulgens, in littoral fine sand
			Bathyporeia pilosa	6	coarse gravels	1.6

Acknowledgements

This work was funded by the Life + Pêche à pied de loisirs Project through the Aires Marines Protégées (EU). This work was also funded by the UPMC, the CNRS and the University of Lille 1. L. De Cubber is funded by a PhD studentship from the University of Lille. We would like to thank C. Rolet for her expertise in Taxonomy to confirm the identification of the species allowing the description of the EUNIS habitats and A. Meirland for interesting discussion regarding the impact of recreational fisherman on lugworms' populations.

higher to what [START_REF] Pires | Expansion of lugworms towards southern European habitats and their identification using combined ecological, morphological and genetic approaches[END_REF] found in Portugal (between 0.25 and 1 individual. m -²). The similar abundance of A. defodiens observed at all sites might be linked to the presence of a subtidal population of this species: when, for some reason, densities of population from the foreshore decrease, the subtidal individuals could colonize the empty spaces and reload the intertidal A. defodiens population. Indeed, the subtidal presence of A. defodiens was recorded in Portugal by [START_REF] Pires | Expansion of lugworms towards southern European habitats and their identification using combined ecological, morphological and genetic approaches[END_REF] and in France on the Eastern English Channel by the present authors (unpublished data). However, the density estimation for A. defodiens was made from data of cast production obtained for A. marina, and further investigation on the cast production of A. defodiens is needed to conclude more accurately on the abundance of this species.

Life-history traits of lugworm

The spawning period of Arenicola marina appeared to occur at the beginning of autumn and at the end of autumn to beginning of winter (at Wx) for A. defodiens. There was a time lag of two weeks to two months between the two species' spawning periods, as previously described by several authors [START_REF] Dillon | Contrasting breeding periodicity of nearby populations of the lugworm, Arenicola marina (Annelida, Polychaeta)[END_REF][START_REF] Watson | Control of oocyte maturation, sperm activation and spawning in two lugworm species: Arenicola marina and Arenicola defodiens[END_REF][START_REF] Watson | Can synchronous spawning be predicted from environmental parameters? A case study of the lugworm Arenicola marina[END_REF], probably to avoid species hybridization which was shown to be possible by in vitro fertilization [START_REF] Watson | Extension of the breeding season and its effects on fertilization and development in two species of lugworm (Arenicola marina and A. defodiens)[END_REF]. For both species, spawning periods vary according to the year. Environmental parameters such as tidal amplitude cycles, temperature (temperature at the beginning of the gametogenesis and temperature just prior to spawning) as well as weather conditions have shown to influence spawning periods in A. marina [START_REF] Watson | Extension of the breeding season and its effects on fertilization and development in two species of lugworm (Arenicola marina and A. defodiens)[END_REF][START_REF] Watson | Can synchronous spawning be predicted from environmental parameters? A case study of the lugworm Arenicola marina[END_REF]. The combination of these environmental parameters may explain the variation of spawning periods between years. In fact, spawning periods recorded in this study for both species are likely to have occurred during spring tides (Supplementary Material: Fig. H), but not at the same water temperature. There was ~ 4°C difference between the minimum and the maximum of water temperature during the spawning period of the different sites for a respective species which might suggest that spring tides may play a role in the triggering of spawning events rather than water temperature. [START_REF] Watson | Can synchronous spawning be predicted from environmental parameters? A case study of the lugworm Arenicola marina[END_REF] suggested for a Scottish population of A.

marina that others spawning cues may be taken into account such as air temperature, air pressure, daily rainfall and/or wind speed, etc.

The size at first maturity found for Arenicola marina at Wx (3.8 cm) corresponds to an individual of approximately 1 g, which is close to the weight at which individuals of A.

marina started developing gametes in the laboratory experiment performed by De Wilde and Berghuis (1979). Recruits of A. marina were only spotted at Wx and recruitment happened