Distribution and Structure of Faunal Assemblages and Their Associated Physical Conditions on the Atlantic Continental Shelf of the British Isles

International Council for the Not to be cited without prior Exploration of the Seas reference to the author

Theme session P: Physical-biological Interactions: Experiments, Models and Observations ICESCM 2004/P:03

Distribution and structure of faunal assemblages and their associated physical conditions on the Atlantic continental shelf of the British Isles

Jim Ellis and Stuart Rogers

There has been an increased use of groundfish surveys as platforms for the sampling of macro-epibenthic fauna over wide geographical areas in recent years. Indeed, internationally coordinated studies have provided spatially comprehensive data for the North Sea. In contrast, the invertebrate fauna off the western coasts of the UK are more poorly known. Macro-epifaunal samples collected by 4m-beam trawl were used to determine the structure and diversity of demersal assemblages occurring along the western seaboard of the British Isles. Samples were collected during 2003 from the Celtic Sea/Bristol Channel (ICES division VIIf-g), Irish Sea (VII a) and the western English Channel (VIIe). Cluster analysis was used to determine the similarity of assemblages in the area, and the distribution of these assemblages was examined in relation to depth, substrate, latitude, water temperature, salinity and tidal stress. Stations in the Irish Sea were characterised by species typical of inshore grounds, including Pagurus bernhardus, Asterias rubens, Ophiura ophiura and Liocarcinus holsatus, with stations on the coarser grounds of the central Irish Sea and English Channel were typified by Pagurus prideaux. The relationships between epibenthic assemblages and the physical environment are discussed.

Keywords: Epibenthic monitoring,

Jim Ellis and Stuart Rogers, CEFAS Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk, NR33 0HT, U.K. [tel: +44 (0)1502 524300, fax: +44 (0)1502 513865, e-mail [email protected]].

INTRODUCTION

It has become apparent in recent years that there is a lack of knowledge of the distribution and structure of offshore benthic species and communities, although such information is required on wide geographical scales (e.g. by ICES area and OSPAR region). Whereas the majority of published accounts of benthic communities have focused on detailed site-specific studies, such localised studies are rarely compatible, due to the differences in timing, gears and sampling protocol. Over recent years, the use of groundfish and monitoring surveys as platforms for the sampling of macro-epifauna and megafauna over wide geographical areas has been undertaken for many sea areas. Regional studies include 4m-beam trawl sampling in the eastern English Channel (Kaiser et al., 1999), southern North Sea (Ellis and Rogers, 1999) and Irish Sea/Bristol Channel (Rees et al., 1999; Ellis et al., 2000), and 2m-beam trawls sampling in the North Sea (Jennings et al., 1999; Rees et al., 1999; Callaway et al., 2002) and Celtic Sea (Ellis et al., 2002). Other studies have incorporated data from such surveys for specific taxa (e.g. Ellis and Rogers, 2000; Ellis et al., 2002; Porter et al., 2002).

The aim of the current study was to describe the structure, composition and distribution of macro-epibenthic invertebrate assemblages in the western English Channel, Bristol Channel, St George’s Channel and Irish Sea using samples collected during a 4m-beam trawl groundfish survey, to determine which physical variables best explained the observed patterns in these assemblages and to determine whether these spatial patterns in invertebrate assemblages had corresponding spatial differences with regards to cephalopods and demersal fishes.

MATERIALS AND METHODS

Sampling stations and sampling protocol Demersal fish and invertebrates were collected from 182 stations in the western English Channel (ICES Division VIIe), Bristol Channel (VIIf) and Irish Sea and St George’s Channel (VII a) during a groundfish survey undertaken by the R.V. Corystes in September 2003 (Figure 1). Fishing was conducted with a 4-metre beam trawl with chain mat and 40 mm stretched mesh cod-end (see Kaiser & Spencer, 1994). Trawling speed was 4 knots and tow duration was 30 minutes at most stations, sampling approximately 15,000 m2 per tow. Certain stations, which were known to result in large quantities of shell debris, macroalgae or excessive numbers of juvenile flatfish, were sampled for 15 minutes.

All fish, cephalopods and commercial shellfish were identified, counted, weighed and measured (see Rogers et al., 1998). The remaining invertebrate catch was weighed and a representative sub-sample of known weight sorted. Invertebrates were identified to the lowest taxonomic level possible, weighed and all non-colonial species counted. Data were subsequently converted to catch per unit effort (CPUE) for both biomass and numbers per hour.

Physical variables Surface water and bottom temperature and salinity were recorded from a micro-CTD attached to the headline of the beam trawl. Surface water temperature and salinity were also recorded from a continuous data logger, though these data were only used when no data from the micro-CTD were available (e.g. in the case of battery failure).

Although no data on the sediments of the trawl stations were available, the general sediment type was estimated from British Geological Survey Charts. For data analysis, sediments were allocated values on the following scale: 1=mud; 2=sandy mud; 3=muddy sand; 4=sand; 5=gravely sand; 6=sandy gravel; and 7=gravel. To provide an additional indication of the ground type, the total weight of rocks in each catch was recorded, and the weight of shell debris in the sub-sample was raised to total catch.

Tidal stress was estimated from a two-dimensional hydrodynamic model of the north-west European shelf, originally developed at the Proudman Oceanographic Laboratory, which had been used to predict the depth-mean

M2 tidal current at a spatial resolution of 1/8° longitude by 1/12° latitude

(approximately 8km). Bed stresses due to the M2 tide were calculated using a quadratic expression, with stress dependent on the predicted maximum ellipse current and an appropriate bed friction coefficient, in this case with an assumed value of 0.0025. Data from this model were used to provide an indication of tidal stress at trawl stations, with stations between values of tidal stress interpolated.

Data analysis The PRIMER analytical package (Clarke and Warwick, 1994) was used for the cluster analysis of trawl data, using the Bray-Curtis similarity on fourth-root transformed CPUE data (kg.hr-1). This transformation was undertaken to downweight the importance of abundant, large-bodied taxa (e.g. common starfish Asterias rubens) and increase the relative importance of smaller- bodied taxa that may be more indicative of ground type. Stations with similar catch compositions were assumed to reflect sites with similar macro- epibenthic assemblages. Discriminating species for each assemblage were identified using the similarity of percentages procedure (SIMPER), which determines the contribution of each species to the average dissimilarity between clusters. SIMPER analysis was also undertaken to examine differences in fish catches (numerical catch data) between groups of stations with the similar macro-epinbenthic invertebrate catches.

The association between physical variables with the similarity of macro- epibenthic invertebrates was determined using the BIOENV routine (Clarke & Warwick, 1994). The biological similarities of the catches at stations were compared with the following physical variables: latitude, depth, the weights of rocks and broken shell in the catch, surface water temperature and salinity (as

recorded during the research cruise) and M2 tidal current. The weights of rocks and broken shell were also transformed (ln(1+weight)) for this analysis. BIOENV analysis was also undertaken to determine which physical variables were best correlated with the catch composition of the dominant taxa. The association between physical variables with the similarity of fish catches was also determined.

RESULTS

Cluster analysis indicated five broad category of macro-epibenthic assemblage, though these clusters could generally be divided into more spatially defined sub-clusters. The majority of stations were broadly divided into two main clusters, broadly equating with shallow-water sandy habitats (61 stations) and coarser grounds (81 stations) that were typically further from shore, though several parts of the western English Channel had coarser grounds close inshore. The distribution of these broad assemblage types are illustrated in Figure 2.

Inshore assemblage The inshore sandy grounds (mean similarity = 44.2%) were dominated by a few common inshore species, such as Asterias rubens, sand star Astropecten irregularis, common hermit crab Pagurus bernhardus, common brittlestar Ophiura ophiura; harbour crab Liocarcinus depurator, swimming crab L. holsatus, common whelk Buccinum undatum and sea mouse Aphrodita aculeata (Table 1). Inshore sandy grounds were sub-divided latitudinally between those in the south (including parts of Cardigan Bay, Carmarthen Bay, Swansea Bay, Bideford Bay and Lyme Bay), and those sites further north in the Irish Sea (e.g. Liverpool Bay, Solway Firth, Dundrum Bay). The principle differences between these two regions were that spider crab Maja squinado and curly weed Alcyonidium diaphanum were more abundant in the southerly, and A. irregularis, L. depurator and L. holsatus more abundant in the northerly area. This assemblage was typical of inshore waters, extending down to 50m in the western English Channel, 60m in the Bristol Channel and 70m in the Irish Sea.

Coarse ground assemblage The coarser grounds of the central Irish Sea, Celtic Sea and western English Channel were relatively similar (mean similarity = 44.5%) and, overall, these grounds were relatively diverse (Table 2). The dominant species included the hermit crab Pagurus prideaux, A. rubens, dead-man’s fingers Alcyonium digitatum, hydroids and queen scallop Aequipecten opercularis. Small-bodied spider crabs, such as scorpion spider crab Inachus dorsettensis and slender spider crab Macropodia tenuirostris, were also abundant. Although this large cluster could be sub-divided into smaller cluster (e.g. the sites in the shallower waters of Lyme Bay and the Irish Sea, sites in the deeper waters of the western English Channel, sites off Plymouth), there were no major differences in the species composition. This assemblage typically occurred at depths of 20–112m in the western English Channel, 30–86m in the Bristol Channel, and 35–80m in the Irish Sea.

Mud assemblage The most unique stations were those on muddy grounds in the north-western Irish Sea (five stations, down to 110m deep), off the coast of Cumbria (three stations, ca. 28m deep), Celtic Sea (one station) and off Brixham (one station at 47m depth). Catches at these ten stations (mean similarity 44.5%) were typified by burrowing megafaunal crustaceans such as Norway lobster Nephrops norvegicus and angular crab Goneplax rhomboides. Mud-dwelling species that were present in some or all of these areas, but for which catch rates were generally lower (Table 3) included the heart urchin Brissopsis lyrifera, pistol shrimp Alpheus glaber, the thalassinoid shrimp Calocaris macandreae, the bivalve Nucula sulcata and the sea-pen Virgularia mirabilis.

Hard ground assemblage A cluster of 23 stations in St George’s Channel, central Irish Sea and parts of the Bristol Channel were also distinctive (mean similarity = 45.2%), with a further two stations in Lyme Bay also relatively similar to these 23 stations (overall mean similarity = 43.3%). Overall, catches at these sites were generally diverse (Table 4) and were dominated by large echinoderms (e.g. A. rubens, green sea urchin Psammechinus miliaris, common sunstar Crossaster papposus) and sessile filter-feeding taxa (A. digitatum, hydroids, ascidians). Small crustaceans, such as pink shrimp Pandalus montagui were also abundant. The two stations in Lyme Bay were dominated by A. diaphanum and A. opercularis, and large aggregations of the tube-forming polychaete Serpula vermicularis were also present. This assemblage extended down to 97m in the Irish Sea, though there was some minor differences between catches in shallower waters and stations in the central Irish Sea and St George’s Channel.

Hard ground assemblage in the Bristol Channel Catches at five stations (30–60m depth) in the outer Bristol Channel were distinct from other stations, and were characterised by a few dominant species (Table 5), principally M. squinado, A. diaphanum and spiny starfish Marthasterias glacialis, and though their average similarity was low (34.1%), these sites were different to other assemblages.

Correlation between invertebrate catches and physical variables The BIOENV analysis indicated that the physical parameters that correlated best with the observed patterns in invertebrate catches (Rank Spearman

correlation rw) were depth (rw=0.36), latitude (rw=0.33), the index of sediment type (rw=0.31), and surface salinity (0.28). Surface water temperature, tidal stress, and the transformed catch rates of rocks and broken shell were less well correlated (rw=0.18, 0.17, 0.13 and 0.08 respectively). The best correlation involving multiple physical parameters was for four variables

(latitude, depth, tidal stress and sediment index, rw=0.52), with the inclusion of surface water temperature resulting in a similar correlation (rw=0.52).

MDS ordination plots, which are a 2-dimensional representation of the similarity of stations, in terms of the abundance (biomass) of invertebrates with overlying data for depth, the transformed weight of rocks and shell debris and tidal stress are illustrated in Figures 3–6.

BIOENV indicated that the dominant invertebrate phyla (Arthropoda, Mollusca, Crustacea), and a combined group of mostly sessile fauna (Cnidaria, Bryozoa, Ascidiacea, Porifera, Polychaeta) were all correlated with

depth and the index of sediment type (rw=0.12–0.33 for depth, and 0.20–0.22 for sediment), and the best correlations with multiple variables ranging from 0.32–0.48 for these four groups (Table 6).

The ichthyfauna associated with epibenthic assemblages Fish and cephalopod catches (CPUE by numbers) were compared between assemblages identified a priori by examination of the invertebrate assemblages. Sand gobies (Pomatoschistus spp.), which were identified to genus level, were omitted from this analysis.

The fish and cephalopods associated with the inshore epibenthic assemblage (stations 50.85% similar) were dominated by dab Limanda limanda, plaice Pleuronectes platessa, solenette Buglossidium luteum, sole Solea solea and common dragonet Callionymus lyra (Table 7). Though C. lyra was still a dominant species on coarser grounds (Table 8), thickback sole Microchirus variegatus, red gurnard Aspitrigla cuculus and poor cod Trisopterus minutus were important species occurring on coarse grounds, and A. cuculus and M. variegatus important disciminating species between the inshore sites and the sites on coarser grounds. The fish catches on the coarse epibenthic assemblages were 46.6% similar.

The fish catches associated with the hard offshore grounds in St George’s Channel and the central Irish Sea (46.47% similar) were broadly similar to those occurring on the coarser grounds, as were the fish catches associated with the hard coastal grounds in the Bristol Channel. Catches on hard ground (Table 9) tended to comprise greater numbers of lemon sole Microstomus kitt than the inshore assemblage, though catch rates of plaice and solenette were greater inshore.

Fish catches on the hard grounds of the Bristol Channel (Table 10) had smaller catches of scaldfish Arnoglossus laterna and solenette in comparison to the inshore assemblage, and the hard assemblages of the central Irish Sea and St George’s Channel tended to have much greater catches of lesser spotted dogfish Scyliorhinus canicula and pogpe Agonus cataphractus.

Fish catches on the mud assemblages (Table 11) were the most dissimilar (mean similarity=21.56%), suggesting that although the invertebrates occurring on mud are quite consistent geographically, there may be bathymetric and/or biogeographical variation in the fishes associating with these discrete habitats. Various flatfishes dominated on muddy habitats.

The mean dissimilarity of catches of invertebrates (biomass) and fish and cephalopods (numbers) between the groups of stations are given in Table 12.

Correlation between fish catches and physical variables The BIOENV analysis indicated that the physical parameters that correlated best with the observed patterns in numbers of fish and cephalopods in the

catches (Rank Spearman correlation) were depth (rw=0.42), the index of sediment type (rw=0.31), latitude (rw=0.29) and surface water temperature

(rw=0.26). Surface salinity, the transformed catch rates of rocks, tidal stress and the transformed catch rates of broken shell were less well correlated

(rw=0.22, 0.20, 0.11 and 0.09 respectively. The best correlation (rw=0.53) incorporated five physical parameters: depth, surface water temperature and the sediment index, latitude and the transformed weight of rocks.

BIOENV indicated that the dominant fish goups (Gadiformes, Pleuronectiformes, large-bodied demersal fish and small-bodied demersal

fish) were all correlated with depth (rw=0.17–0.43). The best correlations with multiple variables ranged from 0.25–0.51 for these four groups (Table 13).

DISCUSSION

An earlier analysis of beam trawl catch data examined demersal assemblages in the Irish Sea and Bristol Channel, though this study undertook cluster analysis of fish and invertebrates together. Even with a severe transformation of the data (fourth root), the data collected are heavily bias towards fish, which may be less indicative of the type of benthic community. The current study has undertaken an analysis of invertebrates from a larger area, including the first quantitative data for the western English Channel (see below), and the observed spatial patterns in assemblage structure were broadly comparable. The analysis of the ichthyofauna associated with these macro-epibenthic assemblages highlighted that several fish species are characteristic of specific communities. For example, the catch rates of Aspitrigla cuculus and Microchirus variegatus are normally much greater on offshore coarse grounds.

The present paper also includes improved data for tidal stress and sediment type, and both these variables. The index of sediment type (from British Geological Survey sediment charts) was found to correlate well with the catch composition of invertebrates, and also for flatfish and small-bodied demersal

fish. The M2 tidal stress data was also correlated with the catch composition of echinoderms, crustaceans and sessile fauna. Whereas hydrographic modelling data are often available over wide geographical areas, most data pertaining to sediment and seabed topography are often held by national organisations. The collation of such information to provide standard data regarding the seabed over the ICES/OSPAR area is required if further progress is to be made for mapping infaunal and epifaunal benthic communities and marine habitats over wide geographical areas. Additionally, there is currently no standardised approach to the nomenclature of demersal assemblages, with authors using the characteristic biota and/or the physical regime to classify assemblages/communities.

The data presented here include the first quantitative data for catches in 4m- beam trawl for the western English Channel. These fishing grounds were typically coarse and dominated by the hermit crab Pagurus prideaux and echinoderms. These grounds also contained invertebrates of high conservation importance, notably the pink sea fan Eunicella verrucosa at four stations in the Plymouth area, one specimen of fan mussel Atrina fragilis (station D-5) and large aggregations of the tube-forming serpulid Serpula vermicularis in Lyme Bay.

REFERENCES

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Porter, J.S., Ellis, J.R., Hayward, P.J., Rogers, S.I. and Callaway, R. (2002). Geographic variation in the abundance and morphology of the bryozoan Alcyonidium diaphanum (Ctenostomata: Alcyonidiidae) in UK coastal waters. Journal of the Marine Biological Association of the United Kingdom, 82:529–535.

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Table 1: Dominant macro-epibenthic fauna of inshore sandy grounds

Species Contrib% Cum.% Asterias rubens 17.02 17.02 Astropecten irregularis a,d 10.23 27.24 Pagurus bernhardus 8.94 36.18 Liocarcinus holsatus c 8.25 44.43 Hydroids 7.16 51.59 Maja squinado 5.95 57.54 Ophiura ophiura 5.57 63.11 Buccinum undatum 5.32 68.43 Aphrodita aculeata 4.48 72.91 Liocarcinus depurator 4.03 76.94 Alcyonidium diaphanum 3.56 80.50 Alcyonium digitatum 3.18 83.68 Cancer pagurus 2.34 86.02 Flustra foliacea 2.31 88.33 Philine aperta 1.76 90.09 a: Catches greater than on hard grounds; b: Catches greater than on coarse grounds; c: Catches greater than on mud; d: Catches greater than on Bristol Channel grounds

Table 2: Dominant macro-epibenthic fauna of coarse offshore grounds

Species Contrib% Cum.% Pagurus prideaux a,b,c,d 10.98 10.98 Asterias rubens d 9.77 20.75 Alcyonium digitatum c,d 9.08 29.83 Hydroids c 7.74 37.57 Aequipecten opercularis 6.56 44.13 Cancer pagurus 4.85 48.98 Inachus dorsetensis b,c,d 4.37 53.35 Astropecten irregularis 4.33 57.68 Pagurus bernhardus 3.97 61.66 Liocarcinus holsatus 3.76 65.41 Alcyonidium diaphanum 3.70 69.11 Marthasterias glacialis 2.60 71.71 Macropodia tenuirostris,b,c 2.52 74.24 Ophiura ophiura 2.15 76.39 Maja squinado 1.99 78.38 Liocarcinus depurator 1.86 80.23 Chaetopterus (tubes) 1.80 82.03 Aphrodita aculeata 1.42 83.45 Pecten maximus 1.39 84.84 Psammechinus miliaris 1.21 86.05 Luidia ciliaris 1.05 87.10 Porifera 0.99 88.09 Ascidiacea indet. 0.94 89.03 Buccinum undatum 0.94 89.97 Flustra foliacea 0.91 90.88 a: Catches greater than on hard grounds; b: Catches greater than on inshore grounds; c: Catches greater than on mud; d: Catches greater than on Bristol Channel grounds

Table 3: Dominant macro-epibenthic fauna of mud grounds

Species Contrib% Cum.% Nephrops norvegicus a,b,c,d 23.65 23.65 Astropecten irregularis a 13.51 37.17 Cancer pagurus 11.34 48.51 Goneplax rhomboides a,b,c,d 10.63 59.14 Pagurus bernhardus 8.29 67.43 Liocarcinus depurator 8.03 75.46 Hydroidea 7.58 83.05 Asterias rubens 7.38 90.43 a: Catches greater than on hard grounds; b: Catches greater than on coarse grounds; c: Catches greater than on inshore grounds; d: Catches greater than on Bristol Channel grounds

Table 4: Dominant macro-epibenthic fauna of hard grounds

Species Contrib% Cum.% Asterias rubens a,d 14.67 14.67 Alcyonium digitatum 11.08 25.75 Hydroids a,c 8.65 34.39 Flustra foliacea 5.74 40.13 Psammechinus miliaris a 4.38 44.51 Crossaster papposus 4.12 48.63 Ascidiacea indet. 3.94 52.57 Pandalus montagui a,b,c,d 3.90 56.46 Liocarcinus holsatus 3.75 60.22 Aequipecten opercularis 3.65 63.87 Alcyonidium diaphanum 3.04 66.91 Buccinum undatum 2.79 69.70 Cancer pagurus 2.56 72.25 Echinus esculentus 2.14 74.39 Liocarcinus depurator 1.83 76.22 Porifera 1.81 78.03 Maja squinado 1.72 79.75 Pagurus bernhardus 1.58 81.34 Dogfish (egg-cases) 1.54 82.88 Hyas coarctatus 1.30 84.18 Macropodia tenuirostris 1.06 85.24 Inachus leptochirus 1.04 86.28 Ophiothrix fragilis 1.03 87.32 Metridium senile 0.92 88.24 Pagurus prideaux 0.91 89.15 Inachus dorsetensis 0.84 89.99 Macropodia rostrata 0.83 90.82 a: Catches greater than on mud grounds; b: Catches greater than on coarse grounds; c: Catches greater than on inshore grounds; d: Catches greater than on Bristol Channel grounds

Table 5: Dominant macro-epibenthic fauna of hard grounds in the Bristol Channel

Species Contrib% Cum.% Maja squinado a,b,d 29.32 29.32 Marthasterias glacialis c,d 18.05 47.37 Alcyonidium diaphanum a,b,c 14.06 61.42 Hydroids 6.63 68.06 Metridium senile 4.76 72.81 Buccinum undatum 4.65 77.46 Liocarcinus holsatus a 3.58 81.04 Sabellaria spinulosa 2.32 83.36 Flustra foliacea 2.11 85.47 Asterias rubens 2.01 87.48 Ophiothrix fragilis 1.41 88.89 Cancer pagurus 1.34 90.23 a: Catches greater than on mud grounds; b: Catches greater than on coarse grounds; c: Catches greater than on inshore grounds; d: Catches greater than on hard grounds

Table 6: Correlation between the similarity of stations (CPUE kg.h-1, fourth root) and single physical variables for invertebrate taxa. Those physical variables that contributed to the best correlation with multiple variables are denoted *.

Sessile Variable Echinodermata Mollusca (a) Arthropoda fauna (b) Depth 0.247* 0.318* 0.332* 0.119* Latitude 0.127 0.159 0.336* 0.261* Sediment 0.204* 0.200* 0.210* 0.222* Surface salinity 0.069 0.172 0.283* 0.236* Surface temp. 0.160 0.049 0.208* 0.048 ln(1+rocks) 0.213* 0.021 0.131* -0.023 Rocks 0.222 -0.005 0.133 -0.046 Tidal stress 0.188* 0.014 0.156* 0.065* ln(1+shell debris) 0.075 0.013 0.055 0.000 Shell debris 0.063 -0.053 0.020 -0.059* Best correlation 0.404 (4) 0.345 (2) 0.481 (7) 0.316 (6) (number of variables) (a) Analysis undertaken for the 164 stations where gastropods and bivalves occurred; (b) Including polychaetes

Table 7: Dominant fish species (by numbers, excluding sand gobies) associated with the inshore macro-epibenthic assemblage

Species Contrib% Cum.% Limanda limanda 13.04 13.04 Pleuronectes platessa 11.55 24.59 Buglossidium luteum 11.50 36.09 Solea solea 10.02 46.11 Callionymus lyra 8.64 54.75 Arnoglossus laterna 7.55 62.30 Eutrigla gurnardus 7.18 69.48 Merlangius merlangus 5.45 74.93 Scyliorhinus canicula 5.24 80.17 Trigla lucerna 5.06 85.23 Trisopterus minutus 3.17 88.40 Agonus cataphractus 2.26 90.67

Table 8: Dominant fish species (by numbers, excluding sand gobies) associated with the coarse macro-epibenthic assemblage

Species Contrib% Cum.% Callionymus lyra 15.83 15.83 Microchirus variegatus 13.26 29.09 Trisopterus minutus 12.29 41.37 Aspitrigla cuculus 9.49 50.87 Solea solea 6.72 57.59 Scyliorhinus canicula 5.42 63.01 Arnoglossus laterna 4.88 67.88 Sepia officinalis 4.71 72.59 Pleuronectes platessa 3.29 75.89 Eutrigla gurnardus 2.56 78.44 Limanda limanda 2.39 80.84 Buglossidium luteum 2.16 83.00 Microstomus kitt 2.10 85.10 Arnoglossus imperialis 1.82 86.92 Agonus cataphractus 1.66 88.58 Lophius piscatorius 1.56 90.15

Table 9: Dominant fish species (by numbers, excluding sand gobies) associated with the hard macro-epibenthic assemblage (40.67% similar)

Species Contrib% Cum.% Trisopterus minutus 15.19 15.19 Callionymus lyra 11.46 26.65 Scyliorhinus canicula 10.79 37.44 Agonus cataphractus 8.37 45.81 Microstomus kitt 6.78 52.59 Eutrigla gurnardus 6.50 59.09 Eledone cirrhosa 4.48 63.56 Merlangius merlangus 4.00 67.56 Microchirus variegatus 3.93 71.49 Solea solea 3.87 75.36 Limanda limanda 3.41 78.77 Aspitrigla cuculus 3.00 81.77 Pleuronectes platessa 2.40 84.17 Sepiola atlantica 1.51 85.69 Trisopterus luscus 1.50 87.19 Leucoraja naevus 1.47 88.66 Raja clavata 1.44 90.10

Table 10: Dominant fish species (by numbers, excluding sand gobies) associated with the hard macro-epibenthic assemblage in the Bristol Channel (40.67% similar)

Species Contrib% Cum.% Callionymus lyra 16.19 16.19 Solea solea 15.56 31.75 Pleuronectes platessa 10.91 42.66 Alloteuthis subulata 7.35 50.01 Limanda limanda 5.54 55.56 Trisopterus minutus 4.72 60.28 Trigla lucerna 4.53 64.8 Eutrigla gurnardus 4.29 69.09 Arnoglossus laterna 4.14 73.24 Microchirus variegatus 4.08 77.32 Aspitrigla cuculus 3.42 80.73 Scyliorhinus canicula 3.39 84.12 Raja brachyura 3.29 87.41 Echiichthys vipera 1.23 88.64 Trisopterus luscus 1.23 89.87 Lophius piscatorius 1.20 91.07

Table 11: Dominant fish species (by numbers, excluding sand gobies) associated with the mud macro-epibenthic assemblage (40.67% similar)

Species Contrib% Cum.% Pleuronectes platessa 25.00 25.00 Glyptocephalus cynoglossus 15.57 40.57 Arnoglossus laterna 11.94 52.51 Limanda limanda 6.92 59.43 Solea solea 6.05 65.48 Buglossidium luteum 5.39 70.87 Trisopterus minutes 4.19 75.05 Lophius piscatorius 3.66 78.72 Merlangius merlangus 3.33 82.05 Scyliorhinus canicula 3.13 85.18 Microchirus variegates 3.09 88.27 Eutrigla gurnardus 2.93 91.21

Table 12: Dissimilarity between clusters of epibenthic assemblages (top right) and the fish catches associated with epibenthic assemblages (bottom left)

Hard Assemblage Inshore Coarse Hard (Bristol Mud Channel) Inshore 65.94 69.71 75.55 74.37

Coarse 63.63 66.61 73.69 79.33

Hard 63.27 60.39 75.88 85.05 (Bristol Channel) Hard-BC 61.21 60.51 63.51 90.11

Mud 74.56 78.10 78.64 77.02 EPIBENTHIC ASSEMBLAGES FISH ASSOCIATED WITH EPIBENTHIC ASSEMBLAGES

Table 13: Correlation between the similarity of stations and physical variables for four fish groups. Those physical variables that contributed to the best correlation with multiple variables are denoted *.

Large-bodied Small-bodied Variable Gadoids (a) Flatfish (b) demersal (c) demersal (d) Depth 0.282* 0.426* 0.173* 0.291* Latitude 0.225 0.202(*) 0.080 0.200* Sediment 0.109 0.281* 0.023 0.204* Surface salinity 0.265* 0.137 0.015 0.156 Surface temp. 0.098 0.233* 0.178* 0.188* Ln(1+rocks) 0.041 0.264* 0.001 0.107 Rocks 0.017 0.269 -0.019 0.096 Tidal stress 0.005 0.115 0.085* 0.025 ln(1+shell debris) -0.026 0.134 0.014 0.064 Shell debris -0.040 0.148(*) -0.004 0.033 Best correlation (number of 0.330 (2) 0.505 (4,6) 0.246 (3) 0.369 (4) variables) (a) analysis undertaken for 14 species from 155 stations; (b) analysis undertaken for 18 species from 155 stations; (c) Including elasmobranchs, conger eel and angler fish, analysis undertaken for 13 species from 157 stations; (d) analysis undertaken for 28 demersal species from 176 stations.

Figure 1a: Trawl stations sampled with 4m-beam trawl in the Irish Sea, St George’s Channel, Bristol Channel and western English Channel in 2003.

55.0

3 4 14 5 2 6 15 7 54.5 16 17 18 9 203 19 10 444 22 425 54.0 424 12 41 42 206 23 405 423 53 43 213 401 27 54 28 408 214 47 30 55 31 53.5 419 49 409 447 220 32 36 38 37 40 229 421 440 302 53.0 441 442

233 313 309 316 52.5 430

416 321

438 443 52.0 519

101131024 501 103 112 136110 131074 109 121 138111 114 105 51.5 139 115 119 135 116 120 502 122 117 130 129 132 503 131 126 51.0 533 504 133 128124 507 508 505

513 C-2 512 B-1B-2 C-1 C-4 511 B-0 B-3 C-5 50.5 D-D-0010 B-4 D-1 E-1 D-4 D-2 D-3 E-5 D-5 E-4 Y-6 H-1 Y-8Y-7 Y-5 A-A-2 1 H-2 H-3F-1 F-2 H-5 X-2 Y-Y-14Y-3 H-4 H-6 F-4 Y-G-2 6 F-5 X-1 I-1 I-2 J-3 I-3 L-3 J-5 L-6 J-4 J-6 I-4 I-6 50.0 X-3 M-1 M-3 M-5 X-9 K-6 X-10 N-1 K-4 X-5 N-3 X-6 P-4 N-6 P-6 N-5 X-8 X-4 X-11 X-12 49.5 X-13 X-7

49.0 -8 -7 -6 -5 -4 -3 -2

Figure 1b: Trawl stations sampled with 4m-beam trawl in the western English Channel in 2003.

513 C-2 512 B-1B-2 C-1 C-4 511 B-0 B-3 C-5 50.5 D-D-0010 B-4 D-1 E-1 D-4 D-2 D-3 E-5 D-5 E-4 Y-6 H-1 Y-8Y-7 Y-5 A-A-12 H-2 H-3F-1 F-2 Y-4 H-5 X-2 Y-1 Y-3 H-4 H-6 F-4 Y-G-62 F-5 X-1 I-1 I-2 J-3 I-3 L-3 J-5 I-4 L-6 J-4 J-6 I-6 50.0 X-3 M-1 M-3 M-5 X-9 K-6 X-10 N-1 K-4 X-5 N-3 X-6 P-4 N-6 P-6 N-5 X-8 X-4 X-11 X-12 49.5 X-13 X-7

49.0 -7 -6 -5 -4 -3 -2 Figure 2: Distribution of macro-epibenthic assemblages (Inshore assemblage denoted with filled circle z, coarse ground assemblage denoted with a filled triangle S, mud assemblage denoted with filled square , hard ground assemblage denoted with a filled star , and hard ground assemblage in the Bristol Channel denoted with an open star ). 55.0

54.5

54.0

53.5

53.0

52.5

52.0

51.5

51.0

50.5

50.0

49.5

49.0 -8 -7 -6 -5 -4 -3 -2 Figure 3: MDS ordination plot showing the 2-dimensional representation of similarity of catches of invertebrates (biomass) at all stations. The overlying bubble plot indicates depth.

Stress: 0.23

505

444 512 X13 511 I6 507 131 X7 Y7 X4 Y6 504 502 513 508 J4 M5 M1 503 X8 N3 N1 M3 132 N6X1P41 X1x90 L6 Y5 J5D1128 x6 X3 213 X2X5 Y8Y2I4 J6 D0O 533 N5 p6501 K4 Y1L3 E4 119 X12 X1 K6Y3 G6 D4 103 Y4 I2129122 309 133 I1I3 519 120D3 E5 F2 D5 H6 321 D0I E1 401J3F1 D2C4H1 124 102 16 F4F5 H3 H5 A2 105B4 425 B3 H4 22 A1 138135 17 416 C5 110 443B2 C2 B042 32 121111101 405 44755 53 54 47H2 440 115 430421 C1 30 143837 43 134 408 442423 419 23 409 22015203 13718 41 441 49 5 313 7 19 130 9 316 424229 302 28 438 139233116 6 4 27 B1 109 40 104 117 114 3214 10 136 31 112 126 2 36 12 206

Figure 4: MDS ordination plot showing the 2-dimensional representation of similarity of catches of invertebrates (biomass) at all stations. The overlying bubble plot indicates the transformed weight of rocks.

Stress: 0.23

505

444 512 X13 511 I6 507 131 X7 Y7 X4 Y6 504 502 513 508 J4 M5 M1 503 X8 N3 N1 M3 132 N6X1P41 X1x90 L6 Y5 J5D1128 x6 X3 213 X2X5 Y8Y2I4 J6 D0O 533 N5 p6501 K4 L3Y1 E4 119 X12 X1 K6Y3 G6 D4 103 Y4 I2129122 309 133 I1I3 519 120D3 E5 F2 D5 H6 321 D0I E1 401J3F1 D2C4H1 124 102 16 F4F5 H3 H5 A2 105B4 425 B3 H4 22 A1 138135 17 416 C5 110 443B2 C2 B042 32 121111101 405 44755 53 54 47H2 440 115 430421 C1 30 143837 43 134 408 442423 419 23 409 22015203 13718 41 441 49 5 313 7 19 130 9 316 424229 302 28 438 139233116 6 4 27 B1 109 40 104 117 114 3214 10 136 31 112 126 2 36 12 206

Figure 5: MDS ordination plot showing the 2-dimensional representation of similarity of catches of invertebrates (biomass) at all stations. The overlying bubble plot indicates the transformed weight of shell debris

Stress: 0.23

505

Figure 6: MDS ordination plot showing the 2-dimensional representation of similarity of catches of invertebrates (biomass) at all stations. The overlying bubble plot indicates the tidal stress

Stress: 0.23

505

444 512 X13 511 I6 507 131 X7 Y7 X4 Y6 504 502 513 508 J4 M5 M1 503 X8 N3 N1 M3 132 N6X1P41 X1x90 L6 Y5 J5D1128 x6 X3 213 X2X5 Y8Y2I4 J6 D0O 533 N5 p6501 K4 L3Y1 E4 119 X12 X1 K6Y3 G6 D4 103 Y4 I2129122 309 133 I1I3 519 120D3 E5 F2 D5 H6 321 D0I E1 401J3F1 D2H1 124 102 16 F4F5 H3 H5 C4 A2 105B4 425 B3 H4 22 A1 138135 17 416 C5 110 443B2 C2 B042 32 121111101 405 44755 53 54 47H2 440 115 430421 C1 30 143837 43 134 408 442423 419 23 409 22015203 13718 41 441 49 5 313 7 19 130 9 316 424229 302 28 438 139233116 6 4 27 B1 109 40 104 117 114 3214 10 136 31 112 126 2 36 12 206