Manuscript Details
Manuscript number PROOCE_2018_81_R2
Title Macrofaunal assemblages in canyon and adjacent slope of the NW and Central Mediterranean systems
Article type Full Length Article
Abstract Macrofaunal assemblages were studied along bathymetric transects in six canyons and four adjacent open slopes of the Mediterranean Sea. The different areas investigated were located approximately along a longitudinal gradient at similar latitudes. Three regions were investigated: the Catalan (from 334 to 1887 m depth), the Ligurian (from 222 to 2005 m depth) and the South Adriatic margins (from 196 to 908 m depth). The analysis of the meso-scale distribution of assemblage structure and biomass showed significant differences among regions, which resulted in high values of δ-diversity. Clear differences in trophic composition were also observed, and a decreasing pattern in the individual body size of macrofaunal organisms moving Eastward. These patterns were apparently linked to changes in food supply, whereas macrofaunal abundance and number of taxa showed a decrease pattern with increasing water depth. When the assemblage structure was compared between canyons and adjacent open slope, a very high β-diversity was observed, indicating that the bottom topography exerted a strong effect on the assemblage characteristics.
Keywords Macrofauna; biomass; biodiversity; deep-sea; canyons; Mediterranean Sea
Manuscript category Biological Oceanography
Corresponding Author Anabella Covazzi Harriague
Order of Authors Anabella Covazzi Harriague, Roberto Danovaro, Cristina Misic
Suggested reviewers Georges Stora, Francisco Sardà, Maite Louzao
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File Name [File Type] Covazzi Harriague et al response to reviewers second round.docx [Response to Reviewers]
Covazzi Harriague et al highlights.docx [Highlights]
Covazzi Harriague et al text revised second round.doc [Manuscript File]
Figure 1.tif [Figure]
Figure 2.tif [Figure]
Figure 3.tif [Figure]
Figure 4.tif [Figure]
Figure 5.tif [Figure]
Figure 6.tif [Figure]
Figure 7.tif [Figure]
Covazzi Harriague et al Tables revised second round.docx [Table]
Covazzi Harriague et al Supporting material second round.docx [Table]
To view all the submission files, including those not included in the PDF, click on the manuscript title on your EVISE Homepage, then click 'Download zip file'. Point by point response to Reviewers. In black the reviewer’s observations and suggestions, in red our response.
-Reviewer 1
Line 130: …..(Gage, 2003). this gradient is CHANGE TO “This” Done
LINES 143-145: CHANGE TO: a very high number of canyons whose complexity reflect the features …. Done
LINE 155 “to tidal currents” I WOULD SPECIFY that tides re negligible in the Mediterranean Done
LINE 196: You should, quote along with Mamouridis et al., 2011 also:
TECCHIO S., RAMÍREZ-LLODRA E., AGUZZI J., FLEXAS M.M., COMPANY J.B., SARDÀ F. 2013. Seasonal fluctuations of deep megabenthos: Finding evidence of standing stock accumulation in a flux-rich continental slope. Progress in Oceanography 118: 188-198
Done
LINE 220: i) SHOULD BE ii) Done
LINES 235-262 THESE INFO SHOULD BE CONDENSED INTO Table 1 adding new columns for N replicates and for R/V name.
The info on the R/V name and sampling period was added in the Table 1. The number of replicates was always 3 and it was reported in the text.
LINE 286: Split the paragraphs (a new argument is starting). Done
LINE 308-309: this is a single phrase and should be joined into the previous paragraph (although it is a different argument). Done
LINE 430 sp SHOULD BE CHANGED TO sp. Done
LINE 505 “Notwithstanding” SHOULD BE CHANGED for “Despite” Done
LINE 517: CHANGE TO (21%) Done
LINE 594: You should also quote:
Coll M., Piroddi C., Steenbeek J., Kaschner K, Ben RaisLasram F., Aguzzi J., et al. 2010. Biodiversity of the Mediterranean Sea: status, patterns and threats. PLoS ONE (5): e11842
Done
LINES 535-637: Quotations need to be added in chronologic mode). Done LINES 681-683: You declare that “…. we observed a lack of relationships between the macrofaunal parameters and grain size”. A DESCRIPTION FO THESE RESULTS SHOULD BE GIVEN IN THE RESULT SECTION (Table S3 should be reported there). Done
LINE 808: eliminate one indent (too large paragraph space). Done
Table 1: ADD SEPARATION IN Catalanmargin, Ligurianmargin Done
Also, ub this table you codes the sampling areas (add the head name in that column) as e.g. Southern Open Slope (SOS) or Cap de Creus Canyon (CCC)…..but then in Tables 3 and 4, those codes are forgotten. Please, choose if eliminate the codes form Table 1 or changes names of areas in Table 3 and 4 for those codes for consistency. Done
In table 3. All percentage values should be with numerals e.g. 3rd line form above of values as
33 0 0 33 0 33 is equals top 99!
We add the decimal values
In Table S1: ALL “sp” should be “sp.” Done
In Table S2. Add space in “…diversity),between” Done
Also here…Canyon and Open Slope should be written with the first capital letters as in the Tables before (and please, DO THE SAME FOR Table S1). Done
Also:
MODIFY “Table S3.Result” for “Table S3. Result” Done
NOT commas for decimals but DOTS as in all other numbers. Done
-Reviewer 2
Dear authors.
I recommend minor revisions. These concerns mostly to the discussion which still needs improvement for a better understanding of it. The authors begin the discussion by explaining the differences in community structure between the three investigated regions, then follow by examining patterns observed in the canyon and open slope within each region. Next, the authors use food availability to explain longitudinal patterns in biomass, individual size and trophic composition and then the same variable to explain the variability in trophic composition between canyon and open slope. Food availability could be used in the canyon vs open slope topic and elaborate the discussion in this part that sometimes is vague. In fact, the reason why there were no differences between canyon and open slope in the Ligurian margin, is at the end of the discussion, while in my opinion it is missing in the part where is discussed the local patterns. Also, the canyon and open slope results discussion has some confusion and inconsistencies. For example, the authors compare changes in the assemblage structure between canyon and open slope that were not significant with significant differences found in community structure with other canyons. Also, the authors give examples of species that can explained the differences in dissimilarity between canyon and open slope but is not clear how the presence of one of these species, the ophiurid Amphiura filiformis in both canyon and open slope explain the dissimilarity. The next part is somehow confusing because the authors indicate studies (Gage et al., 1995; Vetter and Dayton, 1999; Curdia et al., 2004) that are in accordance with the present results in relation to the lower number of taxa found inside some canyons but next indicate discrepancy of these findings with previous studies. It is not clear which results and in which canyons are the authors referring to establish the comparison.
I indicate these and other minor comments throughout the discussion in the document. In addition, some comments in the remaining sections, also indicated in the document.
We reorganized the Discussion following carefully all the reviewer suggestions and we took into account all the reviewer comments indicated in the document.
Introduction
Missing reference in the sentence:
“The analyses conducted on macrofaunal assemblages along longitudinal gradients at large spatial- scales (from the Gulf of Lyon to the Ligurian Sea and Southern Adriatic) in the Mediterranean Sea support the important role of these variables and the importance of these systems in promoting deep-sea biodiversity. “
This sentence was deleted
Material and methods:
Please indicate the dissimilarity measure used in the MDS (bray Curtis measure). Done
Please indicate how diversity was estimated (number of taxa). Done
Results:
In the subsection Macrofaunal assemblage structure please change “more significant” to “significant”. Done
In the subsection Macrofaunal biomass please add the results of the regression analysis of biomass according to the longitude.
For the relationship between individual biomass and longitude we have highlighted a general trend. A statistical analysis such as regression was not performed because longitude data were considered not a quantitative parameter as, for instance, depth is, but something more similar to a nominal variable. The individual biomass data in each area (Catalan, Ligurian and South Adriatic margins) are referred to very similar longitude values, therefore regression output would be somehow influenced by this homogeneity. Maybe the sentence was misleading, suggesting that a regression result should exist. We change the sentence.
Some comments on figures and tables:
Figure 2: The legend should indicate that the two MDS images correspond to two different analysis.
Done
The authors indicate that the available data on mud contribution to the sediment composition were added but is missing.
The data of mud contribution to the sediment composition are presented in Table 1 (the last column)
A table with the ANOSIM results for the trophic composition should also be added.
We added the ANOSIM results for the trophic composition in the table 2
Finally, some typos were assigned throughout the text. Macrofauna was studied along bathymetric transects in three areas of the Mediterranean
Canyons and open slopes were investigated in Catalan, Ligurian and South Adriatic margins
Assemblages were significantly different among regions, as shown by high δ-diversity
This was likely due to changes in food supply as a consequence of the longitudinal position
Canyons and adjacent open slope showed a very high β-diversity 1 2 3 Macrofaunal assemblages in canyon and adjacent slope of the 4 5 6 NW and Central Mediterranean systems 7 8 9 10 11 12 Anabella Covazzi Harriague1, Roberto Danovaro2,3, Cristina Misic1 13 14 1DisTAV – Università di Genova – Genoa, Italy 15 16 2DiSVA – Università Politecnica delle Marche – Ancona, Italy 17 18 3 Stazione Zoologica Anton Dohrn –Naples, Italy 19 20 21 22 23 24 Submitted for publication to: Progress in Oceanography 25 26 Date of submission: 6th April 2018 27 28 Date of submission of the amended version: 30th November 2018 29 30 31 32 33 34 35 36 37 38 39 40 41 42 Corresponding author: 43 44 Dr. Anabella Covazzi Harriague 45 46 Dipartimento di Scienze della Terra, dell’Ambiente e della Vita - Università di Genova 47 48 49 C.so Europa 26 - 16132 Genova, Italy 50 51 Phone: 0039 01035338224 52 53 e-mail: [email protected] 54 55 56 57 58 1 59 60 61 62 63 Abstract 64 65 66 Macrofaunal assemblages were studied along bathymetric transects in six canyons and four 67 68 adjacent open slopes of the Mediterranean Sea. The different areas investigated were located 69 70 approximately along a longitudinal gradient at similar latitudes. Three regions were 71 72 investigated: the Catalan (from 334 to 1887 m depth), the Ligurian (from 222 to 2005 m 73 74 depth) and the South Adriatic margins (from 196 to 908 m depth). The analysis of the meso- 75 76 scale distribution of assemblage structure and biomass showed significant differences among 77 78 regions, which resulted in high values of δ-diversity. Clear differences in trophic composition 79 80 were also observed, and a decreasing pattern in the individual body size of macrofaunal 81 82 83 organisms moving Eastward. These patterns were apparently linked to changes in food 84 85 supply, whereas macrofaunal abundance and number of taxa showed a decrease pattern with 86 87 increasing water depth. When the assemblage structure was compared between canyons and 88 89 adjacent open slope, a very high β-diversity was observed, indicating that the bottom 90 91 topography exerted a strong effect on the assemblage characteristics. 92 93 94 95 Key words: Macrofauna, biomass, biodiversity, deep-sea, canyons, Mediterranean Sea. 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 2 119 120 121 122 123 1. Introduction 124 125 126 The Mediterranean Sea is characterised by a clear gradient in primary productivity with 127 128 lowest values in the eastern basin (Danovaro et al., 1999). Since food supply to deep-sea 129 130 benthic fauna depends on the productivity of the euphotic zone (Gage, 2003). This gradient is 131 132 typically reflected by a decreasing abundance, biomass and species richness of the deep 133 134 benthic assemblages moving eastward (Tselepides et al., 2000; Danovaro et al., 2008; Tecchio 135 136 et al., 2011). One of the reasons for the extreme oligotrophy of the eastern Mediterranean 137 138 basin is phosphorous depletion (Salihoglu et al., 1990), while in the western region the fluvial, 139 140 atmospheric and upwelling inputs contribute to a higher productivity (Bas, 2009). Another 141 142 143 main feature of the Mediterranean continental margins is the presence of a very high number 144 145 of canyons, whose complexity reflect the features of the fluvial basins of the continent (Bas, 146 147 2009). 148 149 Submarine canyons contribute to the formation of a number of different habitats that show 150 151 spatial as well as temporal variability, and are often characterised by peculiar benthic 152 153 assemblages (Curdia et al., 2004). The dynamic characteristics of these environments, subject 154 155 to tidal currents albeit tides are negligible in Mediterranean, sediment gravity flows and 156 157 turbidity changes (Canals et al., 2006; de Stigter et al., 2007), increase the physical forcing, 158 159 habitat heterogeneity and the complexity of the morphological features of the seafloor (Thistle 160 161 162 and Levin, 1998). Canyons are areas with enhanced transfer of materials from the continental 163 164 shelf to bathyal depths (Epping et al., 2002; Martin et al., 2006; Sanchez-Vidal et al., 2008; 165 166 Thomsen et al., 2017), and provide an important food supply to the deep-sea benthos (Epping 167 168 et al., 2002; Gunton et al., 2015). The canyons act also as collectors of land-derived organic 169 170 material, which contribute to shape and sustain benthic assemblages (de Stigter et al., 2007). 171 172 For instance, massive inputs of organic materials, including macrophyte detritus (Rowe et al., 173 174 1982; Vetter and Dayton, 1999), are transported from the shelf to the deep sea during periodic 175 176 177 178 3 179 180 181 182 183 flushing events (Canals et al., 2006). These processes contribute to make the Mediterranean 184 185 186 canyons hotspots of benthic production and ecosystem functioning (Vetter and Dayton, 1999; 187 188 Pusceddu et al 2010; Fernández-Arcaya et al., 2017) and are responsible for their generally 189 190 high macrofaunal abundance and biomass (Vetter and Dayton, 1999; Duineveld et al. 2001; 191 192 Gunton et al. 2015). For this reason, studies conducted in Mediterranean Sea have, in many 193 194 cases, highlighted the presence of differences between canyons and the adjacent open slopes 195 196 (Mamouridis et al., 2011; Tecchio et al., 2013). Such differences include also the presence of 197 198 some taxa that are exclusively or preferentially associated to canyon sediments (Bianchelli et 199 200 al., 2010) and are the result of the combined action of habitat heterogeneity and food 201 202 203 availability. 204 205 In the present study, macrofaunal assemblages were investigated within the frame of several 206 207 cruises conducted in different regions at depths comprised approximately from 200 to 2000 m 208 209 depth. The following hypotheses were tested: i) structural and functional features of the 210 211 macrofaunal assemblages among different continental margins change along a longitudinal 212 213 gradient; ii) macrofaunal variables change between canyons and adjacent open slopes in the 214 215 same area. 216 217 218 219 2. Material and Methods 220 221 222 Sampling strategy 223 224 Samples were collected in the Western and Central Mediterranean Sea during several 225 226 multidisciplinary oceanographic cruises. Three regions were studied from 196 to 2005 m 227 228 depth. The Catalan margin was sampled during the HERMES cruises in the Gulf of Lyon (11 229 230 sampling stations), the Ligurian margin was sampled during the BioLig (Ligurian Canyons) 231 232 cruise (12 sampling stations) and the South Adriatic margin was sampled during the 233 234 235 236 237 238 4 239 240 241 242 243 CANYON BARI 2006 (SETE-06) cruise (11 sampling stations) (see Figure 1, Table 1 for 244 245 246 details). 247 248 Three replicate samples were collected in each station, using either multi-corer (3 maxicorer, 249 250 with inner diameter 9.3 cm for each replicate) and box-corer (29x29 cm). On board, all the 251 252 sediment collected was washed and sieved through 500 µm mesh size. After that, the residual 253 254 was frozen at -20°C. 255 256 257 258 Macrofaunal variables 259 260 In laboratory, sediment of all the stations was sorted and organisms were identified down to 261 262 263 species level (Table S1), whenever possible, and counted. Taxonomical identification (Fauvel, 264 265 1923; 1927; Parenzan, 1976; Bellan-Santini et al., 1982; 1989; 1993; Pancucci-Papadopoulou 266 267 et al., 1999) was checked with the World Register of Marine Species 268 269 (http://www.marinespecies.org). The number of taxa, intended as a proxy of diversity, was 270 271 calculated for each station 272 273 To determine the biomass, organisms were dried at 60°C for 24 hours and weighed. Data of 274 275 number of organisms and weight were normalised to square meter to determine abundance 276 277 and biomass applying the following formula: abundance/biomass = organism 278 279 number/organism weight of the sample/sampled area in square meter. The individual biomass 280 281 282 of organisms was calculated as the ratio between biomass and abundance. Trophic groups 283 284 were determined according to Fauchald and Jumars, 1979; Jangoux and Lawrence, 1982; 285 286 Grahame, 1983; Russell-Hunter, 1983 and Gambi and Giangrande, 1985. 287 288 289 290 Statistical analyses 291 292 The PRIMER 6 package (Clarke and Warwick 2001) on presence/absence data was used to 293 294 perform the multidimensional scaling (MDS, Bray-Curtis similarity index) and the analysis of 295 296 297 298 5 299 300 301 302 303 similarities (ANOSIM), to test the differences in community structure within and between the 304 305 306 sites. Moreover the similarity percentages-species contributions (SIMPER) was performed, 307 308 based on a Bray-Curtis similarity matrix, to evaluate the turnover local diversity (hereafter 309 310 called β-diversity) and regional turnover diversity (hereafter called δ-diversity) (Gray, 2000; 311 312 Danovaro et al., 2009). In order to homogenize the data, the taxonomical level family was 313 314 used for all analysis. The analysis of similarities (ANOSIM) was performed on the 315 316 presence/absence data of the trophic composition in order to verified differences between 317 318 sites. The relationship between community parameters and depth and mud contribution to the 319 320 sediment composition were verified with the regression analysis. 321 322 323 324 325 3. Results 326 327 Macrofaunal assemblage structure 328 329 The MDS ordination (Figure 2) showed that the stations of the Ligurian margin are grouped 330 331 together, while the other two sites are not clearly separated. Notwithstanding, the analysis of 332 333 similarities (ANOSIM) showed significant differences in the structure of the communities 334 335 between the three regions (Table 2A). 336 337 The trophic composition of the assemblages was significantly different between the Ligurian 338 339 margin and the Catalan and South Adriatic margins (ANOSIM, Table 2B). 340 341 342 δ-diversity between the three regions was high: Catalan margin vs Ligurian margin 97% (4 343 344 common taxa: Cirolanidae, Golfingidae, Nuculidae, Paraonidae), Catalan margin vs South 345 346 Adriatic margin 97% (3 common taxa: Canalipalpata, Terebellidae, Xanthidae) and Ligurian 347 348 margin vs South Adriatic margin 98% (3 common taxa: Copepoda, Phascolosomatidae, 349 350 Spionidae). Each region was characterized by different taxa that determined the regional 351 352 variability: in the Ligurian margin the main part of them belonged to polychaetes, while in the 353 354 355 356 357 358 6 359 360 361 362 363 Catalan margin the half of the taxa and in the South Adriatic margin only one family belonged 364 365 366 to this class (Figure 3). 367 368 369 370 - Catalan margin 371 372 The macrofaunal abundance varied between 0 and 254.6±28.9 ind × m-2 (average 91.2±24.1 373 374 ind. × m-2). The highest values were found in the shallowest stations of the NOS and LDC 375 376 (Table 3). The average value was higher in the open slope station than in the canyon ones 377 378 (Figure 4A). The distribution of abundances was significantly influenced by the depth (Figure 379 380 5A). On the whole 30 taxa were identified, 14 in the canyon and 17 in the open slope 381 382 383 assemblages, notwithstanding the average values of the two areas were quite similar (Figure 384 385 4B). Canyon and open slope communities showed only 1 common taxa, leading to a very high 386 387 local β-diversity (95%; Table S2). Although the community structure did not show a 388 389 significant differences between habitats (Table 2A). The number of taxa, instead, did not 390 391 show a significant relationship with depth (Figure 5B). The structural parameters did not 392 393 show any correlation with the contribution of the mud fraction (Table S3). Assemblages were 394 395 dominated by Annelida (50%), followed by Crustacea (19%), Echinodermata (13%), 396 397 Sipuncula (10%), Mollusca (5%) and others (Platyhelminthes and Nemertea; 3%). The first 398 399 group was the most important in the canyon area, reaching 70% of the abundance, while in 400 401 402 the open slope area 86% of the abundance was composed by Annelida, Crustacea and 403 404 Echinodermata (Table 3). The trophic structure of the communities was different in the two 405 406 areas: in the assemblages of the canyons the principal contributors to the abundance were 407 408 organisms with mixed strategies, deposit-suspension (such as Onchnesoma steenstupii 409 410 steenstupii and Terebellidae) and deposit-grazer feeders (such as Notomastus sp.), while in the 411 412 open slope assemblages suspension feeders (such as Jassa marmorata and Thalassema gigas), 413 414 415 416 417 418 7 419 420 421 422 423 deposit feeders (such as Chaetopteridae and Paraonidae) and predators (such as Ancistrosyllis 424 425 426 cf. groenlandica) were the most abundant (Figure 6). 427 428 429 430 - Ligurian margin 431 432 The higher abundances were observed in the shallow stations (see Table 3). The maximum 433 434 value was 396.4±97.4 ind × m-2 in the shallow station of the PC and the minimum 15.0±15.0 435 436 ind. × m-2 in the deepest station of the LMOS (average 141.6±39.2 ind. × m-2). Contrary to the 437 438 Catalan margin, the average abundance in the canyon areas was slightly higher than that 439 440 observed in the open slope ones (see Figure 4A). In general, a significant decreasing trend of 441 442 443 macrofaunal abundance with depth was observed (see Figure 5A). In the Ligurian margin 43 444 445 taxa were found, 23 in the open slope area and 34 in the canyons, and 14 were observed in 446 447 both areas. Here the β-diversity was 82%, the lowest of the three sites (Table S2). Despite, the 448 449 community structure of the both habitats did not differ significantly (Table 2A). The average 450 451 values of the number of taxa were higher in the canyon (see Figure 4B). A significant 452 453 decrease of the number of taxa with depth was observed (Figure 5B). The structural 454 455 parameters did not show any correlation with the contribution of the mud fraction (Table S3). 456 457 Total abundance was composed by Annelida (76%) and Crustacea (15%). In the canyon areas 458 459 these groups represented 70% and 15%, respectively, of the total abundance, while in the 460 461 462 open slope assemblages they represented 83% and 12% respectively (see Table 3). From a 463 464 trophic point of view, the composition of the assemblages in the canyons and open slope was 465 466 quite similar, being dominated by deposit feeders (such as Maldanidae and Onuphidae) (55% 467 468 and 60%, respectively), followed by predators (such as Eunicidae and Lumbrineridae) (18% 469 470 and 14%, respectively) and deposit-suspension feeders (such as Spionidae and Urothoe cf. 471 472 elegans) (13% and 11%, respectively) (see Figure 6). 473 474 475 476 477 478 8 479 480 481 482 483 - South Adriatic margin 484 485 486 The higher abundance was observed in the shallowest station of the open slope 487 -2 488 (2747.3±1066.7 ind. × m ), while the deepest stations of the two canyons showed the 489 -2 490 minimum value (0 ind. × m , see Table 3). A significant decrease of the abundance with 491 492 depth was observed (see Figure 5A). Between the two areas, the open slope displayed a higher 493 494 average value than canyon one (see Figure 4A). On the whole, 22 taxa were found in the 495 496 South Adriatic margin, 13 in the open slope and 12 in the canyon areas. Despite the similar 497 498 number, the average values were different, open slope displayed the highest one (see Figure 499 500 4B). Only 3 taxa were common at the two areas and the β-diversity was 88% (Table S2). 501 502 503 Nevertheless, the analysis of similarities didn’t show significant differences between the two 504 505 habitats (Table 2). The number of taxa showed a significant decrease trend with depth (see 506 507 Figure 5B). Abundance did not show any correlation with the contribution of the mud 508 509 fraction, while a significant correlation was found for the number of taxa (Table S3). 510 511 Communities were composed by Crustacea (28%) followed by Annelida (22%), 512 513 Echinodermata (21%), Mollusca (14%), others (Nematoda) (10%) and Sipuncula (5%). 514 515 Assemblages on the canyon areas were composed principally by 35% of Mollusca and 35% of 516 517 Echinodermata, while in the open slope, the Annelida and Crustacea reached 72% of the total 518 519 abundance (see Table 3). Also, the trophic composition was different for the two areas: in the 520 521 522 canyon sites 70% of the abundance was represented by suspension feeders (such as Amphiura 523 524 filiformis and Clausinella fasciata), while in the open slope 77% was represented by deposit- 525 526 suspension feeders (such as Spionidae), deposit feeders-predators (such as Nematoda) and 527 528 predators (such as Acanthephyra eximia) (see Figure 6). 529 530 531 532 Macrofaunal biomass 533 534 535 536 537 538 9 539 540 541 542 543 Values of biomass and the relative contribution of each taxa to the biomass are presented in 544 545 546 Table 4. The decapod Xantho pilipes was the responsible for the highest value (13422.9 mg × 547 -2 548 m ) observed in the shallowest station of the SOS in the Catalan margin. The contribution of 549 550 the different groups was quite similar for Ligurian and South Adriatic margins, but in the 551 552 Catalan margin 93% of the total biomass was due to Crustacea and Echinodermata. The three 553 554 sites showed a distribution of the biomass in the canyon and open slope areas similar to the 555 556 abundance one (see Figure 4C). In general, macrofaunal biomass did not show a significant 557 558 relationship with depth. Only in the Catalan margin a significant decrease of the values with 559 560 increasing water depth was observed (see Figure 5C). Biomass did not show any correlation 561 562 563 with the contribution of the mud fraction (Table S3). 564 565 The individual biomass was determined, highlighting a general decreasing trend moving 566 567 eastward. The highest values were observed in the western area (Figure 7A). The average 568 569 value for the canyon areas was 1.7± 1.1, 1.4±1.4 and 1.3±1.6 mg ind-1 for the Catalan, 570 571 Ligurian and South Adriatic Margins respectively. A high variability was observed for the 572 573 open slope values: 40.4±67.5, 0.3±0.2 and 2.6±2.5 mg ind-1 for the Catalan, Ligurian and 574 575 South Adriatic Margins respectively. The relationship with depth was not significant (R = 576 577 0.1735, n = 32, p>0.05; Figure 7B). 578 579 580 581 582 4. Discussion 583 584 The ANOSIM analysis indicated the presence of significant differences in the structure of the 585 586 macrobenthic assemblages among the different sampling regions along the longitudinal 587 588 gradient. Such differences were observed also in terms of high turnover diversity among 589 590 different investigated regions which resulted in a high δ-diversity. Only Oligochaeta and, 591 592 within the polychaetes, the family Capitellidae, were reported from all of the investigated 593 594 regions. The observed variability at regional scale of the macrofaunal assemblages is 595 596 597 598 10 599 600 601 602 603 apparently linked to the specific environmental features, including differences in primary 604 605 606 productivity and organic carbon fluxes, which decreased moving Eastward, with consequent 607 608 decrease of the organic matter available to consumers in deep-sea sediments (Gambi and 609 610 Danovaro, 2006; Coll et al., 2010). Also the temporal variability should be considered, the 611 612 regions were sampled in different years and different seasons. The importance of food source 613 614 in structuring deep-sea assemblages was underlined also by Mamouridis et al., (2011) who 615 616 reported seasonal changes in macrofaunal communities of the Besos canyon. 617 618 The trophic composition of macrofaunal assemblages showed differences between the three 619 620 regions, in accordance with the differences reported in terms of food availability (Pusceddu et 621 622 623 al., 2010). In fact, where the quality and quantity of the sedimentary organic matter were 624 625 higher, such as in the Catalan margin, the dominant trophic guild were the deposit feeders and 626 627 suspension-deposit feeders. Conversely, in the South Adriatic margin where lower food 628 629 resources where available the macrofaunal assemblages were dominated by suspension 630 631 feeders and predators. The predator contribution to the abundance (Figure 6) increased from 632 633 West to East. All meiofaunal variables investigated in the same expeditions decreased moving 634 635 Eastward (Bianchelli et al. 2010), we could hypothesize a predatory pressure of the 636 637 macrofauna on meiofauna and/or competition between those benthic compartments. On the 638 639 other hand, the food resources in the sediment of Mediterranean Sea decrease eastward 640 641 642 reaching a strong oligotrophic condition in the Levantine basin (Danovaro et al. 1999). In 643 644 such conditions predators are facilitated in obtaining food due to their higher motility 645 646 (Danovaro et al., 2008). The same result was reported by Baldrighi et al. (2014) from the 647 648 analysis of the deep macrofaunal assemblages across a longitudinal gradient in Mediterranean 649 650 open slopes. 651 652 653 654 655 656 657 658 11 659 660 661 662 663 The structure of the assemblages within each of the three regions changed also comparing the 664 665 666 two habitats considered (canyon and open slope). Such changes resulted in high values of the 667 668 β-diversity between the habitats. Duineveld et al. (2001) and Gunton et al. (2015), comparing 669 670 the Whittard canyon with the adjacent continental slope, reported significant differences in 671 672 macrofaunal assemblages. The macrofaunal dissimilarity between canyons and slopes 673 674 reported in the present study was slightly higher than that reported for the rare taxa of the 675 676 meiofaunal communities in the Catalan and South Adriatic margins by Bianchelli et al. 677 678 (2010), and higher than the dissimilarity for the nematodes assemblages for the same regions 679 680 (Danovaro et al., 2009). One possible explanation of the observed patterns is that the fauna 681 682 683 inhabiting each habitat are adapted to the local environmental features such as the dynamic 684 685 characteristics of the canyons, where there is a large transport of energy and materials from 686 687 the shelf to the deep-sea (Vetter and Dayton, 1998; 1999; Canals et al., 2006; de Stigter et al., 688 689 2007). For instance, we found some individuals of the bivalve Thyasira flexuosa inside the 690 691 Polcevera canyon and a conspicuous population of the ophiurid Amphiura filiformis inside 692 693 both canyons, eight-fold higher than in the open slope, in the South Adriatic region. Both 694 695 species are considered as indicators of high organic matter loads. In fact, the bivalve belongs 696 697 to the first order opportunistic group and the ophiurid to the second order opportunistic group 698 699 (Simboura and Zenetos, 2002). 700 701 702 The lower number of taxa in canyons than in adjacent slopes observed in the Catalan and 703 704 Adriatic margins, are consistent with a number of other studies (Gage et al., 1995; Vetter and 705 706 Dayton, 1999; Curdia et al., 2004). 707 708 Previous studies of macrofauna in canyons reported higher abundance and biomass than in the 709 710 adjacent slope (Duineveld et al., 2001). This holds true also for the Ligurian margin, where 711 712 the macrofaunal assemblages of the canyon stations showed a higher abundance than those of 713 714 the slope, but contrasts with the Catalan and South Adriatic margins where an opposite 715 716 717 718 12 719 720 721 722 723 pattern was reported. As previously mentioned, one of the key factors driving the community 724 725 726 structure of the deep-sea fauna is the food supply (Ruhl and Smith, 2004). Previous studies 727 728 conducted in the Catalan and South Adriatic margins (Pusceddu et al. 2010) showed that the 729 730 food availability was similar in canyon and open slope habitats. These findings are consistent 731 732 with the macrofaunal distribution observed in the present study. In addition, the mud 733 734 contribution to the sediment composition was quite similar between the two habitats in all 735 736 regions studied. Also water depth played a potentially important role in structuring 737 738 macrofaunal assemblages in both habitats at the Ligurian and South Adriatic systems, and this 739 740 finding is in accordance with the observations reported in other areas such the Toulon Canyon 741 742 743 (Stora et al., 1999) and the Aviles Canyon (Louzao et al., 2010). 744 745 The local variability observed also between the topographic habitats in the Catalan and South 746 747 Adriatic systems, can contribute to explain the observed differences, as the Catalan canyons 748 749 dominated by organisms with mixed trophic strategies (deposit-suspension feeders and 750 751 deposit feeders-grazers), pointing to the role of organic materials transported from the shelf to 752 753 the deep-sea habitats (such as macrophyte detritus, Rowe et al., 1982; Vetter and Dayton, 754 755 1999) during periodic flushing events and sedimentation of the transported material (Canals et 756 757 al., 2006). Conversely, the South Adriatic, was dominated by suspension feeders, confirming 758 759 the importance of primary production and the export of organic matter to the deep sea 760 761 762 (Pusceddu et al., 2010). In the Ligurian margin the trophic composition of macrofaunal 763 764 assemblages did not show differences between canyon stations and slope ones, and this 765 766 finding is consistent with the fact that the two habitats showed similar amount of bioavailable 767 768 organic matter (Carugati et al., this issue). 769 770 771 772 The trophic characteristics of the sediments (as quality and quantity of sedimentary organic 773 774 matter) of the Catalan and South Adriatic margins (Pusceddu et al., 2010) can also contribute 775 776 777 778 13 779 780 781 782 783 to explain the observed patterns in macrofaunal biomass, with highest values in the Catalan 784 785 786 margin and a decreasing pattern Eastward. These findings are consistent with patterns 787 788 observed for meiofauna by Gambi and Danovaro (2006) and are reflected also by patterns in 789 790 individual size of the organisms, which decreased moving Eastward according to the 791 792 depletion of the available food source (Pusceddu et al., 2010). Finally water depth did not 793 794 play an important role in driving these faunal variables (see Figure 5C and 7B). We also 795 796 observed the lack of any relationships between macrofauna and grain size (Table S3) 797 798 suggesting that the textural characteristics did not play any significant key role in controlling 799 800 the faunal distribution. 801 802 803 804 805 In conclusion, the analyses conducted on macrofaunal assemblages along longitudinal 806 807 gradients at large spatial-scales (from the Gulf of Lyon to the Ligurian Sea and Southern 808 809 Adriatic) in the Mediterranean Sea suggest that canyons by increasing β-diversity (i.e., the 810 811 species turnover between canyons and open slopes) due to the spatial and trophic variability 812 813 observed between canyons and slopes and among the different biogeographic regions. 814 815 816 817 Acknowledgements 818 819 This study has been conducted in the framework of the Projects: HERMES (Hotspot 820 821 822 Ecosystem Research on the Margin of European Seas), MERCES (Marine Ecosystem 823 824 Restoration in Changing European Seas; Grant Agreement No. 689518), DG-ENV project 825 826 IDEM: Implementation of the MSFD to the Deep Mediterranean Sea (contract EU No 827 828 11.0661 /2017/750680/SUB/EN V.C2), and RITMARE (Ricerca Italiana per il Mare) funded 829 830 by the Ministero dell’Istruzione, dell’Università e della Ricerca. 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Macrobenthic 1170 1171 community structure over the continental margin of Crete (South Aegean Sea, NE 1172 1173 Mediterranean). Prog Oceanogr 46: 401–428. 1174 1175 Vetter E.W., Dayton P.K. 1998. Macrofaunal communities within and adjacent to a detritus- 1176 1177 rich submarine canyon system. Deep Sea Research II 45, 25–54. 1178 1179 Vetter E.W., Dayton P.K. 1999. Organic enrichment by macrophyte detritus, and abundance 1180 1181 1182 patterns of megafaunal populations in submarine canyons. Marine Ecology Progress Series 1183 1184 186, 137–148. 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 20 1199 1200 1201 1202 1203 Figure captions 1204 1205 1206 Figure 1. Location of the sampling stations in the three sites of Western and Central 1207 1208 Mediterranean Sea. Black circles: open slope stations, grey circles: canyon stations. 1209 1210 Figure 2. The multidimensional scaling (MDS) applied on presence/absence data of the three 1211 1212 regions considered. The upper panel represents the analysis of all the data, in the lower panel 1213 1214 are presented the results of analysis excluding the three outliers. 1215 1216 Figure 3. Results of the SIMPER analysis between the three regions and characteristic taxa . 1217 1218 Figure 4. Average values ± standard error of A: abundance, B: number of taxa, C: biomass. 1219 1220 Fig. 5. Linear regression between depth and macrofaunal parameters in the three sites. A: 1221 1222 1223 abundance, B: number of taxa and C: biomass. 1224 1225 Fig. 6. Relative abundance of the trophic groups in the assemblages of the two topographic 1226 1227 habitats (canyon and open slope) in the three sites studied. Susp: suspension feeders, dep- 1228 1229 susp: deposit-suspension feeders, dep: deposit feeders, dep-graz: deposit feeders-grazers, dep- 1230 1231 pred: deposit feeders-predators, pred: predators. 1232 1233 Fig. 7. Relationship between organism individual size vs longitude (A) and vs depth (B). 1234 1235 Black triangles represent the average value; standard error is indicated, when not visible it is 1236 1237 included in the marker size. 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 21 1259 1260 1261 1262 1263 Supporting Material 1264 1265 1266 Table S1. Complete list of taxa found in the three studied areas. 1267 1268 Table S2. Species contributions, in percent, to the dissimilarity (diversity), between canyon 1269 1270 and open slope within each site. 1271 1272 Table S3. Result of the regression analysis between the contribute of the mud fraction to the 1273 1274 sediment composition and the principal macrofaunal parameters. 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 22 1319 1320 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 1 2 3 Table 1. Station depth, geographic coordinates, sampling device and percentage of mud in the sediment 4 texture. N.d.: not determined. 5 6 7 Depth Latitude Longitude Sampling Mud 8 9 (m) N E device % 10 Catalan Southern Open Slope (SOS) 398 42° 08.85' 03° 35.06' multi-corer 69 11 margin 985 42° 07.72' 03° 46.63' 87 12 1887 42° 07.05' 04° 02.74' 77 13 R/V Universitatis Cap de Creus Canyon (CCC) 960 42° 18.47' 03° 36.60' 80 14 October 2005 1434 42° 12.64' 03° 49.22' 86 15 16 R/V Thetys II 1870 42° 12.88' 04° 15.43' 68 17 August 2006 Lacaze-Duthiers Canyon (LDC) 434 42° 34.44' 03° 24.04' 76 18 990 42° 26.56' 03° 31.83' 80 19 1497 42° 21.96' 03° 49.41' 56 20 Northern Open Slope (NOS) 334 42° 34.13' 03° 39.19' 71 21 1022 42° 26.49' 03° 51.32' 77 22 23 Ligurian Open Slope (LMOS) 222 44° 18.79' 08° 40.22' box-corer 98 24 margin 507 44° 16.22' 08° 40.30' 99 25 1054 44° 11.37' 08° 40.52' 99 26 R/V Minerva Uno 1516 44° 03.40' 08° 39.16' 99 27 May 2013 2005 43° 55.02' 08° 38.17' 96 28 Polcevera Canyon (PC) 252 44° 21.87' 08° 49.33' 99 29 540 44° 21.23' 08° 50.19' n.d. 30 31 963 44° 18.72' 08° 49.88' 94 32 1623 44° 10.58' 08° 45.71' 99 33 Bisagno Canyon (BC) 225 44° 21.13' 08° 54.74' 96 34 496 44° 20.12' 08° 54.64' 92 35 1946 44° 00.71' 08° 49.10' 98 36 South Adriatic Canyon B (CB) 370 41° 22.10' 17° 06.70' multi-corer 39 37 38 margin 446 41° 21.71' 17° 07.75' 65 39 590 41° 20.63' 17° 11.02' 19 40 N/O Urania Open Slope (SAMOS) 196 41° 21.30' 17° 05.96' 11 41 May 2006 406 41° 20.08' 17° 10.32' 44 42 908 41°13.70' 17° 35.15' 68 43 Canyon C (CC) 341 41° 19.07' 17° 05.15' 1 44 45 435 41° 19.47' 17° 09.75' 63 46 593 41° 18.18' 17° 12.51' 57 47 618 41° 18.84' 17° 14.66' 48 48 721 41° 18.43' 17° 15.61' 58 49 50 51 52 53 54 55 56 57 58 59 60 61 62 Table 2. Results of Analysis of similarities (ANOSIM), applied on the presence/absence data, between sites 63 (Catalan margin, Ligurian margin and South Adriatic margin) and between Canyon and Open Slope inside 64 65 each site. A): abundance of taxa matrix, B): abundance of trophic groups matrix. 66 67 68 69 A) R p 70 Catalan margin vs Ligurian margin 0.409 0.001 71 72 Catalan margin vs South Adriatic margin 0.150 0.018 73 Ligurian margin vs South Adriatic margin 0.505 0.001 74 75 76 Catalan margin 77 78 Canyon vs Open Slope -0.066 0.667 79 Ligurian margin 80 Canyon vs Open Slope 0.142 0.138 81 South Adriatic margin 82 83 Canyon vs Open Slope -0.142 0.786 84 85 86 B) R p 87 88 Catalan margin vs Ligurian margin 0.222 0.005 89 Catalan margin vs South Adriatic margin 0.072 0.186 90 91 Ligurian margin vs South Adriatic margin 0.392 0.002 92 93 94 Catalan margin 95 Canyon vs Open Slope 0.263 0.079 96 Ligurian margin 97 98 Canyon vs Open Slope 0.058 0.290 99 South Adriatic margin 100 Canyon vs Open Slope 0.194 0.190 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 Table 3. Station depth, total abundance (mean±standard error), number of taxa and percentage of the 124 contribution of the main taxa to the total abundance. An: Annelida, Cr: Crustacea, Mo: Mollusca, Si: 125 Sipuncula, Ec: Echinodermata, Ot: others. 126 127 128 N. 129 Depth Total abundance taxa An Cr Mo Si Ec Ot 130 ind * m-2 % % % % % % 131 2 50 50 0 0 132 Catalan Southern Open Slope (SOS) 398 84.9±11.5 0 0 133 margin 985 81.2±44.4 9 48 4 9 26 0 13 134 1887 63.7±21.2 3 33.34 0 0 33.32 0 33.34 135 Cap de Creus Canyon (CCC) 960 109.4±17.9 9 56 15 21 8 0 0 136 1434 21.2±11.5 1 100 0 0 0 0 0 137 1870 0 0 0 0 0 0 0 0 138 Lacaze-Duthiers Canyon (LDC) 434 203.7±28.9 4 62 0 13 25 0 0 139 0 0 0 0 0 140 990 0 0 0 141 1497 63.7±17.3 1 100 0 0 0 0 0 142 Northern Open Slope (NOS) 334 254.6±28.9 2 50 0 0 0 50 0 143 1022 127.3±23.1 1 0 100 0 0 0 0 144 Ligurian Open Slope (LMOS) 222 364.6±57.2 15 85 11 2 0 2 0 145 margin 507 95.1±41.2 7 83 17 0 0 0 0 146 2 80 0 0 20 0 147 1054 59.5±11.7 0 148 1516 44.6±14.9 3 67 33 0 0 0 0 149 2005 15.0±15.0 1 100 0 0 0 0 0 150 Polcevera Canyon (PC) 252 396.4±97.4 15 76 10 8 2 4 0 151 540 83.2±54.8 5 57 29 14 0 0 0 152 963 198.2±28.6 16 56 24 0 20 0 0 153 1623 38.6±8.9 3 100 0 0 0 0 0 154 155 Bisagno Canyon (BC) 225 291.3±48.7 10 85 7 8 0 0 0 156 496 55.5±28.6 7 72 14 14 0 0 0 157 1946 57.7±57.7 3 33 67 0 0 0 0 158 South Canyon B (CB) 370 183.0±83.3 2 50 0 50 0 0 0 159 Adriatic 446 457.9±183.3 3 20 0 0 20 60 0 160 margin 590 0 0 0 0 0 0 0 0 161 9 23 47 0 7 10 13 162 Open Slope (SAMOS) 196 2747.3±1066.7 163 406 183.0±57.7 2 50 0 0 0 50 0 164 908 274.7±126.7 2 67 33 0 0 0 0 165 Canyon C (CC) 341 915.8±366.7 6 10 0 70 0 0 20 166 435 91.5±46.2 1 0 100 0 0 0 0 167 593 274.5±144.3 1 0 0 0 0 100 0 168 1 0 0 0 0 100 0 169 618 183.0±86.6 170 721 0 0 0 0 0 0 0 0 171 172 173 174 175 176 177 178 179 180 Table 4. Station depth, total biomass (mean±standard error) and percentage of the contribution of the main 181 taxa to the total biomass. An: Annelida, Cr: Crustacea, Mo: Mollusca, Si: Sipuncula, Ec: Echinodermata, Ot: 182 183 others. 184 185 186 187 Depth Total biomass An Cr Mo Si Ec Ot 188 -2 189 mg *m % % % % % % 190 Catalan Southern Open Slope (SOS) 398 13546.8±7505.6 1 99 0 0 0 0 191 margin 985 545.2±397.4 15 1 0 2 0 82 192 1887 385.6±172.5 8 0 0 28 0 64 193 Cap de Creus Canyon (CCC) 960 314.9±187.9 51 16 1 32 0 0 194 1434 12.4±6.4 100 0 0 0 0 0 195 0 0 0 0 0 0 196 1870 0 197 Lacaze-Duthiers Canyon (LDC) 434 355.2±173.2 85 0 9 6 0 0 198 990 0 0 0 0 0 0 0 199 1497 1.9±0.6 100 0 0 0 0 0 200 Northern Open Slope (NOS) 334 7471.4±692.8 0.03 0 0 0 99.97 0 201 1022 43.3±23.1 0 100 0 0 0 0 202 94 2 4 0 0 0 203 Ligurian Open Slope (LMOS) 222 132.6±67.3 204 margin 507 11.6±7.8 62 38 0 0 0 0 205 1054 21.2±12.7 81 0 0 19 0 0 206 1516 23.2±19.6 84 16 0 0 0 0 207 2005 0.1±0.1 100 0 0 0 0 0 208 Polcevera Canyon (PC) 252 1620.4±885.7 45 53 0 0 2 0 209 540 108.9±82.6 12 86 2 0 0 0 210 85 2 0 13 0 0 211 963 93.8±31.1 212 1623 17.5±14.9 100 0 0 0 0 0 213 Bisagno Canyon (BC) 225 628.1±79.3 99 1 0 0 0 0 214 496 13.5±9.8 97 1 2 0 0 0 215 1946 65.6±65.6 37 63 0 0 0 0 216 South Canyon B (CB) 370 675.4±115.5 76 0 24 0 0 0 217 6 0 0 21 73 0 218 Adriatic 446 17.4±15.6 219 margin 590 0 0 0 0 0 0 0 220 Open Slope (SAMOS) 196 1435.8±1132.1 4 95 0 0.4 0.5 0.1 221 406 999.3±346.4 57 0 0 0 43 0 222 908 527.4±317.5 7 93 0 0 0 0 223 Canyon C (CC) 341 27.7±20.2 3 0 95 0 0 2 224 435 131.8±49.1 0 100 0 0 0 0 225 0 0 0 0 100 0 226 593 400.8±109.7 227 618 680.9±173.2 0 0 0 0 100 0 228 721 0 0 0 0 0 0 0 229 230 231 232 233 234 235 236 1 2 3 Supporting Material 4 5 Table S1. Complete list of taxa found in the three studied areas. The taxonomical level used for 6 7 statistical analysisis reported in bold. Und.: undetermined or damaged specimens that cannot be 8 determined for their conditions; juv.: juvenile specimens; “+ and -”: are for present and absent. 9 South Adriatic 10 Catalan margin Ligurian margin 11 margin Open Open Open 12 Canyon Canyon Canyon Slope Slope Slope 13 14 Phylum Arthropoda 15 Subphylum Crustacea 16 Class Malacostraca 17 Order Decapoda 18 Infraorder Caridea 19 20 Caridea und. - - + - - - 21 Family Acanthephyridae 22 Acanthephyra eximia - - - - - + 23 Infraorder Brachyura 24 Family Leucosiidae 25 26 Ebalia sp. - - - - - + 27 Family Xanthidae 28 Xantho pilipes - + - - - + 29 Infraorder Gebiidea 30 31 Family Thalassinidae - + - - - - 32 Order Amphipoda 33 Amphipoda und. - - + - - - 34 Infraorder Lysianassida 35 Family Ampeliscidae 36 37 Ampelisca sp. - - - + - - 38 Family Phoxocephalidae 39 Harpinia cf. dellavallei - - + - - - 40 Harpinia truncata - - - + - - 41 Paraphoxus oculatus - - - + - - 42 43 Family Urothoidae 44 Urothoe cf. elegans - - + + - - 45 Infraorder Corophiida 46 Family Ischyroceridae 47 Jassa marmorata - + - - - - 48 49 Family Corophiidae 50 Leptocheirus cf. mariae - - + - - - 51 Infraorder Hadziida 52 Family Maeridae 53 54 Othomaera schmidtii - - - + - - 55 Infraorder Amphilochida 56 Family Oedicerotidae 57 Westwoodilla caecula - - + - - - 58 59 60 61 62 63 Order Isopoda 64 Superfamily Anthuroidea 65 Family Antheluridae 66 Pilosanthura cf. fresii - - + - - - 67 Family Anthuridae - - - - + - 68 69 Superfamily Cymothooidea 70 Family Cirolanidae 71 Natatolana borealis + - + - - - 72 Infraorder Epicaridea + - - - - - 73 Order Cumacea 74 75 Cumacea und. + - - - - - 76 Family Lampropidae 77 Platysympus typicus - - + - - - 78 Family Leuconidae 79 80 Leucon (Epileucon) longirostris - - - + - - 81 Order Tanaidacea 82 Superfamily Apseudoidea 83 Family Apseudidae 84 Fageapseudes retusifrons - - - + - - 85 86 Class Hexanauplia 87 Subclass Copepoda - - + + - + 88 Class Ostracoda 89 Order Podocopida 90 Family Cyprididae - - + - - - 91 92 Phylum Annelida 93 Class Polychaeta 94 Polychaeta und. + - - + + + 95 Subclass Sedentaria 96 Infraclass Canalipalpata 97 98 Canalipalpata und. + + - - + - 99 Family Spionidae - - + + - + 100 Family Ampharetidae - - + + - - 101 Family Terebellidae + - - - - - 102 103 Polycirrus sp. - - - - - + 104 Infraclass Scolecida 105 Family Capitellidae - + + + - + 106 Notomastus sp. + - - - - - 107 Family Maldanidae - - + + - - 108 109 Family Ophelidae + - - - - - 110 Family Orbinidae - - + - - - 111 Family Paraonidae - + + + - - 112 Family Chaetopteridae - + - - - - 113 Subclass Echiura 114 115 Order Echiuroidea 116 Family Thalassematidae 117 118 119 120 121 122 Maxmuelleria gigas - + - - - - 123 Subclass Errantia 124 Order Eunicida 125 FamilyEunicidae - - + + - - 126 Family Lumbrineridae - - + + - - 127 128 Family Onuphidae - - + + - - 129 Order Phyllodocida 130 Family Acoetidae - - + - - - 131 Family Sigalionidae - - + - - - 132 Family Glyceridae - - + + - - 133 134 Family Paralacydonidae - - - - + - 135 Family Pilargidae 136 Ancistrosyllis cf. groenlandica - + - - - - 137 Family Nereididae - + - - - - 138 139 Family Syllidae - - - + - - 140 Family Phyllodocidae - - + - - - 141 Class Clitellata 142 Subclass Oligochaeta + - + + - + 143 Phylum Mollusca 144 145 Class Bivalvia 146 Order Pectinida 147 Family Pectinidae 148 Aequipecten opercularis - - - - + - 149 Order Arcida 150 151 Family Arcidae 152 Bathyarca philippiana - - - - + - 153 Order Venerida 154 Family Veneridae 155 Clausinella fasciata - - - - + - 156 157 Pitar rude - - - - + - 158 Lajonkairia lajonkairii - - - - + - 159 Superfamily Galiommatoidea 160 Family Lasaidae 161 162 Kellia suborbicularis + - - - - - 163 Order Nuculida 164 Family Nuculidae 165 Ennucula tenuis - - + + - - 166 Nucula sulcata + - + - - - 167 168 Order Nuculanida 169 Family Nuculanidae 170 Nuculana fragilis - + - - - - 171 Nuculana sp. juv. + - - - - - 172 Order Lucinida 173 174 Family Thyasiridae 175 Thyasira flexuosa - - + - - - 176 177 178 179 180 181 Phylum Echinodermata 182 Class Ophiuroidea 183 Ophiuridea juv. - - - + - - 184 Order Amphilepidida 185 Family Amphiuridae 186 187 Amphiura chiajei - - - - - + 188 Amphiura filiformis - - - - + + 189 Order Ophiurida 190 Family Ophiuridae 191 Ophiura lacertosa - - + - - - 192 193 Class Echinoidea 194 Subclass Euechinoidea - + - - - - 195 Phylum Sipuncula - 196 Sipuncula und. - - - - - + 197 198 Class Sipunculidea 199 Order Golfingiida 200 Family Golfingiidae 201 Golfingia (Golfingia) elongata - - + - - - 202 Golfingia sp. - + - - - - 203 204 Nephasoma (Nephasoma) constrictum - - + - - - 205 Family Phascolionidae 206 Onchnesoma steenstupii steenstupii + + - - - - 207 Onchnesoma sp. + - - - - - 208 Class Phascolosomatidea 209 210 Order Phascolosomatida 211 Family Phascolosomatidae 212 Phascolosma (Fisherana) capitatum - + - - - - 213 Phascolosoma (Phascolosoma) agassizii - - + - + - 214 Phascolosoma (Phascolosoma) granulatum - - + + - - 215 216 Phylum Platyhelminthes 217 Class Rhabditophora 218 Order Proseiata 219 Family Monocelididae 220 221 Boreocelis sp. - + - - - - 222 Phylum Nematoda - - - - + + 223 Phylum Nemertina - + - - - - 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 Table S2. Percentage contribution of the various taxa to the dissimilarity (diversity) between 240 241 canyon and open slope within each sampling site. Rel. abun.: relative abundance; Cum. cont.: 242 cumulative contribution; 0: absence; “+”: higher abundance; “-“: lower abundance. 243 244 Catalan margin 245 diversity = 95% 246 247 Open Slope Canyon 248 Rel. abun. Rel. abun. Cum. cont.% 249 Oligochaeta 0 + 11.70 250 Ischyroceridae + 0 19.96 251 Phascolionidae - + 27.98 252 Capitellidae 253 - + 35.40 254 Euechinoidea + 0 41.05 255 Pilargidae + 0 46.70 256 Nereidae + 0 51.74 257 Xanthidae + 0 56.79 258 259 Terebellidae 0 + 61.70 260 Monocelididae + 0 65.40 261 Thalassematidae + 0 69.11 262 Nuculidae 0 + 72.58 263 Ophelidae 0 + 75.57 264 265 Canalipalpata - + 78.41 266 Nuculanidae 0 + 80.68 267 Ligurian margin 268 diversity = 82% 269 270 Open Slope Canyon 271 Rel. abun. Rel. abun. Cum. cont.% 272 Onuphidae + - 8.41 273 Paraonidae - + 15.72 274 Lumbrineridae - + 21.17 275 276 Maldanidae + - 26.32 277 Eunicidae + - 30.67 278 Nuculidae + - 34.64 279 Glyceridae - + 38.44 280 Phascolosomatidae + - 42.04 281 282 Thyasiridae + 0 45.64 283 Capitellidae + - 48.61 284 Syllidae 0 + 51.34 285 Caridea + 0 54.01 286 Apseudidae 287 0 + 56.65 288 Orbinidae + 0 59.27 289 Ampharetidae + - 61.88 290 Cirolanidae + 0 64.48 291 Oligochaeta + - 67.01 292 293 Sigalionidae + 0 69.26 294 295 296 297 298 Copepoda 299 + - 71.39 300 Spionidae - + 73.25 301 Cypridinidae + 0 75.09 302 Phoxocephalidae - + 76.92 303 Urothoidae - + 78.63 304 305 Ophiuridae - + 80.32 306 South Adriatic margin 307 diversity = 88% 308 Open Slope Canyon 309 Rel. abun. Rel. abun. Cum. cont.% 310 311 Amphiuridae + - 16.08 312 Terebellidae + 0 27.80 313 Oligochaeta + 0 36.99 314 Leucosiidae + 0 45.28 315 Acanthephyridae 316 + 0 52.39 317 Nematoda + - 58.48 318 Veneridae 0 + 63.07 319 Anthuridae 0 + 67.44 320 Spionidae + 0 71.73 321 322 Canalipalpata 0 + 75.12 323 Pectinidae 0 + 78.51 324 Capitellidae + 0 81.54 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 Table S3. Result of the regression analysis between the mud fraction to the sediment composition 358 359 and the principal macrofaunal parameters. ns: not significant. 360 361 362 363 R n p 364 Catalan margin 365 Density vs Mud fraction 0.2588 9 ns 366 Number of taxa vs Mud fraction 0.4569 9 ns 367 Biomass vs Mud fraction 0.2717 9 ns 368 369 370 Ligurian margin 371 Density vs Mud fraction 0.0265 10 ns 372 Number of taxa vs Mud fraction 0.2280 10 ns 373 Biomass vs Mud fraction 0.1517 10 ns 374 375 South Adriatic margin 376 377 Density vs Mud fraction 0.5643 9 ns 378 Number of taxa vs Mud fraction 0.6192 9 < 0.05 379 Biomass vs Mud fraction 0.2149 9 ns 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413