Soft-bottom Diversity Patterns in Marine Caves; Lessons from Crustacean Community

Depósito de investigación de la Universidad de Sevilla https://idus.us.es/ “This is an Accepted Manuscript of an article published by Elsevier in: JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY on 2013, available at: https://doi.org/10.1016/j.jembe.2013.04.009” 1 Soft-bottom diversity patterns in marine caves; lessons from 1 crustacean community. 2 3 Carlos Navarro-Barranco1, José M. Guerra-García1, Luis Sánchez-Tocino2, Pablo 4 Jiménez-Prada1, Sara Cea1, José Carlos García-Gómez1 5 6 1 Laboratorio de Biología Marina, Dpto. Fisiología y Zoología, Facultad de Biología, 7 Universidad de Sevilla. Avda Reina Mercedes 6, 41012 Sevilla, Spain. 8 2 Departamento de Biología Animal, Facultad de Ciencias, Universidad de Granada. 9 Campus Universitario de Fuentenueva, s/n., 18071 Granada, Spain. 10 11 Corresponding author. Carlos Navarro Barranco. Laboratorio de Biología Marina, Dpto. 12 Fisiología y Zoología, Facultad de Biología, Universidad de Sevilla. Avda Reina 13 Mercedes 6, 41012 Sevilla, Spain. E-mail: ca[email protected]. Tel: +34 954556229. 14 15 ABSTRACT 16 17 The marine caves studies are generally qualitative, focused on hard benthic 18 communities and are carried out in single caves. Therefore, the main ecological patterns 19 of such assemblages are poorly known, especially in soft bottoms. The aim of this study 20 was to test, for the first time, if there are constant diversity patterns in the macroinfauna 21 inhabiting submarine caves. The soft-bottom crustacean fauna of six Mediterranean 22 marine caves, never investigated until now, was studied using a multifactorial design. 23 Two stations were selected in each cave, one inside the cavity and the other in the 24 2 exterior area, to compare the differences between the crustacean communities of both 25 habitats. The caves selected had a wide range of profundity in order to explore the 26 influence of depth on the community. External sediments showed higher values of 27 species richness, and a significant decline in diversity values inside the caves is a 28 constant pattern in all caves studied. The abundance of organisms was strongly 29 influenced by depth: Deeper cave stations had lower number of individuals than 30 external stations, whereas at shallow sites caves provide a more stable environment, 31 which allows higher density of individuals. In contrast to was observed was in hard 32 benthic communities, small scale variability was similar outside and into the caves. The 33 results of this study also reflect that although an endemic cave fauna was not found, the 34 species composition at each cave was clearly different from that present in the exterior 35 habitat and also from that present in another caves sediments. This high variability and 36 strong individuality observed in soft soft-bottom marine caves suggest that there are 37 many and complex factors controlling these communities. 38 39 Keywords; Marine caves, Soft bottom communities, Crustaceans, Diversity patterns, 40 Mediterranean Sea. 41 42 1. INTRODUCTION 43 44 Marine ecologists and taxonomists have been attracted to submarine caves due 45 to the distinctive faunistic, biocenotic and ecological features of these habitats (Riedl 46 1966, Pérès 1967, Sarà 1974, Ott & Svoboda 1976, Cicogna et al. 2003). Although 47 marine cave assemblages were of great interest over the last decade, the knowledge of 48 3 marine cave environments is still fragmentary, because most studies are focused on a 49 small number of taxa and small geographic areas. 50 Most of the efforts in submarine caves have been devoted to the study of hard 51 benthic communities, whereas the number of investigations dealing with the 52 macroinfauna is very scarce (Akoumianaki & Hughes 2004, Bamber et al. 2008, 53 Monteiro-Marques 1981, Navarro-Barranco et al. 2012). Moreover, marine cave studies 54 are mainly qualitative, providing inventories of species and descriptions of distribution 55 patterns for several taxa. Only a few quantitative and experimental studies were 56 developed to determine the main factors governing the structure and organization of 57 marine cave habitats (e.g. Gili et al. 1986, Zabala et al. 1989, Benedetti-Cecchi et al. 58 1996, 1998, Denitto et al. 2007). However, these works were generally carried out in 59 single caves, and therefore their results are difficult to extrapolate to other caves or 60 geographic areas. Although several quantitative studies were conducted simultaneously 61 in different caves, they were focused on hard-substrate communities (Bibiloni et al. 62 1989, Bussotti et al. 2006, Martí et al. 2004a). As a result, there is a lack of studies 63 dealing with the ecology of soft-bottom cave communities, and the general ecological 64 patterns of the main descriptors in these communities are still unknown. 65 Using a multifactorial sampling design, the spatial variation (submarine caves 66 vs. external habitats) of the soft-bottom crustacean community is explored in six 67 different marine caves of the coast of Granada (south Spain). There are many reasons 68 why crustacean community is considered as case study to explore ecological patterns in 69 soft bottoms: Among the macrobenthic fauna inhabiting marine sediments, crustaceans 70 are one of the most diverse and abundant groups (Dauvin et al. 1994, Prato and 71 Biandolino 2005, Lourido et al. 2008). Iliffe (2005) indicated that this group makes up 72 4 90% of species for anchialine caves. Moreover, crustaceans play an important role in 73 structuring benthic assemblages (Duffy and Hay 2000), and they are also sensitive to 74 many environmental conditions, such as depth (Carvalho et al. 2012), sediment 75 composition (De Grave 1999) and pollution (Gómez-Gesteira & Dauvin 2000, Guerra76 García & García-Gómez 2004, de-la-Ossa-Carretero et al. 2012). 77 The study area is a karstic region with a relatively low human impact, which 78 allow us to have many submarine caves with little anthropogenic influence and, a 79 priori, similar characteristics in a short stretch of coastline (about 30 km). The caves 80 selected have a wide range of depth (5–30 m deep); hence, the possible influence of the 81 depth in the patterns found can be explored. Riedl (1966) indicates that a displacement 82 associated with the depth occurs in caves communities. When depth increases, cave 83 species move towards the entrance due to the attenuation of light, hydrodinamism etc. 84 outside the cave. To our knowledge, no other studies were carried out to test the 85 importance of depth in marine cave communities. 86 Consequently, the main objective of this study is to assess diversity patterns of 87 soft-bottom crustacean community according to the depth and the location inside vs. 88 outside of marine caves. 89 90 2. MATERIALS AND METHODS 91 2.1. Study site 92 Six karstic marine caves of the Granada’s coast were selected to carry out this study 93 (Figure 1): Cueva de las Gorgonias (GR) (36°44’17’’ N, 46°46’42’’O, 6 m deep), 94 Cueva de Cantarriján (CN) (36°44’16’’N, 3°46’41’’O, 8 m deep), Cueva de los Treinta 95 Metros (TM) (36°43’12’’N, 3°44’9’’O, 30 m deep), Raja de la Mona (RM) 96 5 (36°43’10’’N, 3°44’6’’O, 30 m deep), Cueva de la Punta del Vapor (PV)(36°43’22’’N, 97 3°42’35’’O, 12 m deep) and Cueva de Calahonda (CL)(36°42’46’’N, 3°22’18’’O, 19 m 98 deep). All of them presented similar length (10–25 m) and morphology, with a single 99 submerged entrance followed by a rectilinear blind-ending tunnel without air chambers. 100 101 2.2. Sample collection 102 Two sampling stations were selected in each cave: one in the exterior area and 103 another inside the cave (each one approximately 10 m from the cave mouth). Four 104 replicate samples were taken for the crustacean study at each station using a hand-held 105 rectangular core of 0.025 m2 to a depth of 10 cm by SCUBA diving. Samples were 106 washed using a 0.5 mm mesh sieve with seawater, fixed with ethanol (70%) and stained 107 with rose bengal. Each sample was examined in the laboratory using binocular 108 microscopes. All crustacean specimens were counted and identified to species level 109 where possible. 110 In addition to the macrofaunal samples, three more sediment cores were 111 collected at each station for physicochemical analyses of the sediments. All samples 112 were immediately stored frozen until the laboratory analyses. Granulometric parameters 113 were determined following the method proposed by Guitián & Carballas (1976). 114 Organic matter and nitrogen percentage in the sediment, together with the composition 115 of phosphorus, lead and copper, were determined following the same methodology of 116 Navarro-Barranco et al. (2012). 117 118 2.3. Data analysis 119 Mean and standard deviation of crustacean abundances, number of species and 120 Shannon-Weaver diversity index (Shannon & Weaver 1963) were calculated for each 121 6 sampling station. Spatial patterns of these parameters were examined using an analysis 122 of variance with the following factors: position (Po), depth (De) and site (Si). Po was a 123 fixed factor with two levels: outside and inside the caves. De, a fixed factor orthogonal 124 with Po, presented three levels: shallow (for caves between 0 and 10 m deep), medium 125 (10–20 m) and deep (20–30 m). Si was a random factor nested with De and with 2 126 levels (two marine caves at each depth level). Four samples of sediment were 127 considered from each cave (n = 4). Prior to ANOVA analyses, the homogeneity of 128 variances was tested using Cochran’s test and appropriate transformations were applied 129 to data when necessary (Underwood 1997). When ANOVA indicated a significant 130 difference for a given factor, the source of difference was identified using the Student131 Newman-Keuls (SNK) tests. 132 Following the same three-factor design, a distance-based permutational 133 multivariate analysis of variance (PERMANOVA, Anderson 2001) was carried out to 134 test differences in the crustacean species composition. A total of 65 variables (taxa) 135 were included in the multivariate data set, and analysis was based on fourth root 136 transformed data. The similarity matrix was calculated using the Bray-Curtis similarity 137 index. Terms found to be significant in the analysis were examined individually using 138 appropriate pair wise comparisons. Non-parametric multidimensional scaling (MDS) 139 was also carried out to examine differences in the crustacean assemblage composition 140 among positions and depths (Clarke & Warwick 1994). The similarity percentages 141 procedure (SIMPER) was used to calculate the contribution of each species to the 142 observed value of the Bray-Curtis similarity among positions and the dissimilarity 143 between positions. A cut-off criterion was applied to allow identification of a subset of 144 species whose cumulative percentage contribution reached 90% of the similarity or 145 dissimilarity values and was considered as ‘important’ in characterizing or separating 146 7 positions. The same three-factor design applied before was used to explore differences 147 in the abundance of the ‘most important species’ characterizing or separating positions. 148 The similarity values for each station (obtained from the comparison among 149 replicates in PERMANOVA) can be used to estimate the small-scale variability in the 150 crustacean assemblage composition. One-way ANOVA was used to test whether the 151 homogeneity in species composition within stations changes between positions. 152 A Principal Component Analysis (PCA) was also carried out to observe the 153 relationships between environmental measures and sampling stations. ANOVAs were 154 performed using the GMAV5 program (Underwood et al. 2002), and multivariate 155 analyses were carried out using the PRIMER v.6 + PERMANOVA package (Clarke & 156 Gorley 2001). 157 158 3. RESULTS 159 160 A total of 65 species were recorded during this study. Thirty six species were 161 found inside the caves, while 58 were present in the exterior stations. In both stations, 162 amphipods were the richest group (Figure 2a), with 43 species in total, followed by 163 cumaceans (9 species), tanaids (6), decapods (4) and isopods (2). Amphipods were also 164 the most abundant group in the study, with approximately 60% of individuals. Inside the 165 cave, tanaids was the group with higher abundance of organisms (Figure 2b). However, 166 their abundance was highly variable (while in Cantarriján cave, 95% of species belong 167 to tanaids; this value was only 5% in the other shallow cave). 168 According to PERMANOVA analysis, there were significant differences in the 169 composition of species between external and internal stations (Table 1), and SIMPER 170 showed a dissimilarity of 83.1% in the species composition between both habitats. 171 8 Within positions, cave stations only presented a similarity of 4.9%, whereas the stations 172 situated outside the caves had 47.7% of similarity. Table 2 showed the most important 173 species in characterizing and separating positions. Only the abundance of Siphonocetes 174 sabatieri, Diogenes pugilator, Megaluropus monasteriensis and Pariambus tipicus were 175 significantly different between positions, with higher abundances in the external 176 stations. Although some taxa, such as all Harpinia species, showed higher abundance 177 inside the caves, no species presented a significant preference to cave stations. The 178 MDS analysis (Figure 3) did not reflect a clear separation in species composition 179 between internal and external stations. Only in some cases, such as medium depth 180 stations, open and cave stations were clearly separated. 181 The three-way ANOVA for diversity, number of species and abundance of 182 individuals showed different patterns for each case (Table 3). Regarding the abundance 183 values, although all caves showed significant differences between internal and external 184 stations (with the exception of Treinta metros cave) (Figure 4), no consistent pattern 185 was found, with Po x De and Po x Si(De) interactions. Species richness was always 186 higher in external stations than in internal stations. However, according to SNK tests, 187 these differences were only significant for Pta Vapor, Calahonda and Raja de la Mona. 188 Diversity values presented the clearest pattern, with significant higher values outside the 189 caves, consistent for all depths and site levels. 190 The similarity values for species composition between replicates within stations 191 are represented in Figure 5. One-way ANOVA did not find significant differences 192 among positions, so it can be assumed that there was similar small-scale variability in 193 both habitats. 194 Table 4 shows the physicochemical characteristics of the sediment for each 195 station. In the PCA analysis (Figure 6), axis 1 explains a 49% of variation and 196 15 355 Bussotti S, Terlizzi A, Fraschetti S, Belmonte G, Boero F (2006) Spatial and temporal 356 variability of sessile benthos in shallow Mediterranean marine caves. Mar Ecol Prog Ser 357 325:109-119 358 359 Carvalho S, Cunha MR, Pereira F, Pousão-Ferreira P, Santos MN, Gaspar MB (2012) 360 The effect of depth and sediment type on the spatial distribution of shallow soft-bottom 361 amphipods along the southern Portuguese coast. Helgol Mar Res DOI 10.1007/S10152362 011-0285-9 363 364 Cicogna F, Bianchi CN, Ferrari G, Forti P (2003) Grotte marine: cinquant’anni di 365 ricerca in Italia. CLEM, Ministero dell’Ambiente e della tutela del Territorio, Rome 366 367 Clarke KR, Gorley RN (2001) PRIMER (Plymouth Routines in Multivariate Ecological 368 Research) v5: User manual/tutorial. PRIMER-E Ltd, Plymouth 369 370 Clarke KR, Warwick RM (1994) Changes in marine communities: an approach to 371 statistical analysis and interpretation. Natural Environment Research Council, UK 372 373 Corriero G, Liaci LD, Ruggiero D, Pansini M (2000) The sponge community of a semi374 submerged Mediterranean cave. Mar Ecol 21: 85-96 375 376 Dauvin JC, Iglesias A, Lorgeré JC (1994) Circalittoral suprabenthic coarse sand 377 community from the Western English Channel. J Mar Biol Assoc UK 74:543-562 378 379 Denitto F, Terlizzi A, Belmonte G (2007) Settlement and primary succession in a 380 shallow submarine cave: spatial and temporal benthic assemblage distinctness. Mar 381 Ecol 28: 35-46 382 383 De Grave S (1999) The influence of sedimentary heterogeneity on within maerl bed 384 differences in infaunal crustacean community. Est Coast Shelf Sci 49:153-163 385 386 16 de-la-Ossa-Carretero JA, Del-Pilar-Ruso Y, Giménez-Casalduero F, Sánchez-Lisazo JL, 387 Dauvin JC (2012) Sensitivity of amphipods to sewage pollution. Est Coast Shelf Sci 388 96:129-138 389 390 Duffy JE, Hay ME (2000) Strong impacts of grazing amphipods on the organization of 391 a benthic community. Ecol Monogr 70:237-263 392 393 Fichez R (1990a) Decrease in allochthonous organic inputs in dark submarine caves, 394 connection with lowering in benthic community richness. Hydrobiologia 207:61-69 395 396 Fichez R (1990b) Absence of Redox Potential Discontinuity in Dark Submarine Cave 397 Sediments as Evidence of Oligotrophic Conditions. Est Coast Shelf Sci 31:875-881 398 399 Gili JM, Riera T, Zabala M (1986) Physical and biological gradients in a submarine 400 cave on the western Mediterranean coast (NE Spain). Mar Biol 90:291-297 401 402 Gómez-Gesteira JL, Dauvin JC (2000) Amphipods are good bioindicators of the impact 403 of oil spills on soft-bottom macrobenthic communities. Mar Pollut Bull 40:1017-1027 404 405 Gray JS (1997) Gradients in marine biodiversity. In: Ormond R, Gage J, Grassle JF 406 (eds) Marine biodiversity: patterns and processes. Cambridge University Press, 407 Cambridge, p 18-34 408 409 Gray JS (2002) Species richness of marine soft sediments. Mar Ecol Prog Ser 244:285410 297 411 412 Guerra-García JM, García-Gómez JC (2004) Crustacean assemblages and sediment 413 pollution in an exceptional case study: a harbour with two opposing entrances. 414 Crustaceana 77:353-370 415 416 Guitián F, Carballas T (1976) Técnicas de análisis de suelos. 2º ed. Pico Sacrp, Santiago 417 de Compostela 418 419 17 Harmelin JG, Vacelet J, Vasseur P (1985) Les grottes sous-marines obscures: un milieu 420 extreme et un remàrquable biotope refuge. Téthys 11:214-229 421 422 Harmelin JG (1997) Diversity of bryozoans in a Mediterranean sublittoral cave with 423 bathyal-like conditions: role of dispersal processes and local factors. Mar Ecol Prog Ser 424 153:139-152 425 426 Hernández-Arana HA, Rowden AA, Attrill MJ, Warwick RM, Gold-Bouchot G (2003) 427 Large-scale environmental influences on the benthic macroinfauna of the souther Gulf 428 of Mexico. Est Coast Shelf Sci 58:825-841 429 430 Hesse PR (1971) Textbook of soil chemical analysis. J.Murray, London 431 432 Hoey GV, Degraer S, Vincx M (2004) Macrobenthic community structure of soft433 bottom sediments at the Belgian continental shelf. Est Coast Shelf Sci 59:599-613 434 435 Iliffe TM (2005) Biodiversity in anchialine caves. In: Culver DC, White WB (eds) 436 Encyclopedia of Caves. Elsevier Academic Press, London, pp 24-30 437 438 Kendall MA, Widdicombe S (1999) Small scale patterns in the structure of macrofaunal 439 assemblages of shallow soft sediments. J Exp Mar Biol Eco 237:127-140 440 441 Levin L, Thomas CL (1988) The ecology of xenophyophores (Protista) on eastern 442 Pacific seamounts. Deep-Sea Res 35:2003-2027 443 444 Lourido A, Moreira J, Troncoso JS (2008) Assemblages of peracarid crustaceans in 445 subtidal sediments from the Ría de Aldán (Galicia, NW Spain). Helgol Mar Res 62:289446 301 447 448 Martí R, Uriz JM, Ballesteros E, Turon X (2004a) Temporal variation of several 449 structure descriptors in animal-dominated benthic communities in two Mediterranean 450 caves. J Mar Biol Ass UK 84:573-580 451 452 18 Martí R, Uriz JM, Ballesteros E, Turon X (2004b) Benthic assemblages in two 453 Mediterranean caves: species diversity and coverage as a function of abiotic parameters 454 and geographic distance. J Mar Biol Ass UK 84:557-572 455 456 Martí R, Uriz JM, Turon X (2005) Spatial and temporal variation of natural toxicity in 457 cnidarians, bryozoans and tunicates in Mediterranean caves. Sci Mar 69:485-492 458 459 Martínez J, Adarraga I (2001) Distribución batimétrica de comunidades 460 macrobentónicas de sustrato blando en la plataforma continental de Guipúzcoa (Golfo 461 de Vizcaya). Bol Inst Esp Oceanogr 17:33-48 462 463 Monteiro-Marques V (1981) Peuplements des planchers envasés de trois grottes sous464 marines de la région de Marseille. Etude préliminaire. Téthys 10:89-96 465 466 Morrisey DJ, Howitt L, Underwood AJ, Stark JS (1992) Spatial variation in soft467 sediments benthos. Mar Ecol Prog Ser 81:197-204 468 469 Navarro-Barranco C, Guerra-García JM, Sánchez-Tocino L, García-Gómez JC (2012). 470 Soft-bottom crustacean assemblages in Mediterranean marine caves: the cave of Cerro471 Gordo (Granada, Spain) as case study. Helgol Mar Res DOI 10.1007/s10152-012-0292472 5 473 474 Norén K, Lindergarth M (2005) Spatial, temporal and interactive variability of infauna 475 in Swedish coastal sediments. J Exp Mar Biol Eco 317:53-68 476 477 Ott JA, Svoboda A (1976) Sea caves as model systems for energy flow studies in 478 primary hard bottom communities. Pubbl Staz Zool Napoli 40:477-485 479 480 Pérès JM (1967) The Mediterranean benthos. Ocenogr Mar Biol Ann Rev 5:449-533 481 482 Poore G, Wilson GDF (1993) Marine species richness. Nature 361:597-598 483 484 19 Prato E, Biandolino F (2005) Amphipod biodiversity of shallow water in the Taranto 485 seas (north-western Ionian Sea). J Mar Biol Assoc UK 85:333-338 486 487 Rex MA (1993) Global-scale patterns of species diversity in the deep-sea benthos. 488 Nature 365:636-639. 489 490 Riedl R (1966) Biologie der Meereshöhlen. Verlag Paul Parey, Hamburg/Berlin 491 492 Robertson MR, Hall SJ, Eleftheriou A (1989) Environmental correlates with amphipod 493 distribution in a Scottish sea loch. Cah Biol Mar 30:243-258 494 495 Ros J, Romero J, Ballesteros E, Gili JM (1989) Buceando en las aguas azules. El 496 bentos. In: Margalef R (ed) El Mediterraneo Occidental. Omega, Barcelona, pp 235-297 497 498 Sanchez-Moyano E, García-Asencio I, García-Adiego E, García-Gómez JC, Leal499 Gallardo A, Ollero C, Fraidías-Amarillo J (2005) Vigilancia ecológica del litoral 500 andaluz. Consejería de Medio Ambiente, Junta de Andalucía, Sevilla 501 502 Sarà M (1974) Il popolamento delle grotte marine: interesse di una salvaguardia. Pub 503 Staz Zool Napoli 40:50-505 504 505 Shannon CE, Weaver N (1963) The mathematical theory of communication. University 506 of Illinois Press, Urbana 507 508 Snelgrove PVR (1998) The biodiversity of macrofaunal organisms in marine sediments. 509 Biodiv Conserv 7:1123-1132 510 511 Snelgrove PVR, Grassle JF, Petrecca RF (1992) Experimental evidence for aging food 512 patches as a factor contributing to high deep-sea macrofaunal diversity. Limnol 513 Oceanogr 41:605-614 514 515 Thrush SF (1991) Spatial patterns in Soft-bottom Communities. TREE 6(3):75-79 516 517 20 True MA (1970) Etude quantitative de quatre peuplements sciaphiles sur substrat 518 rocheux dans la region marsellaise. Bull Inst Océanogr Monaco 69(1401):1-48 519 520 Turon X, Martí R, Uriz JM (2009) Chemical bioactivity of sponges along an 521 environmental gradient in a Mediterranean cave. Sci Mar 73:387-397 522 523 Underwood AJ (1997) Experiments in Ecology: Their Logical Design and Interpretation 524 Using Analysis of Variance. Cambridge University Press, Cambridge 525 526 Underwood AJ, Chapman MG, Richards SA (2002) GMAV-5 for Windows. An 527 analysis of variance programme. University of Sydney, Australia. 528 529 Vacelet J, Boury-Esnault N, Harmelin JG (1994) Hexactinellid cave, a unique deep-sea 530 habitat in the scuba zone. Deep-Sea Res 41(7):965-973 531 532 Zabala M, Riera T, Gili JM, Barange M, Lobo A, Peñuelas J (1989) Water flow, trophic 533 depletion, and benthic macrofauna impoverishment in a submarine cave from the 534 western Mediterranean. Mar Ecol 10:271-287 535 536 FIGURE LEGENDS 537 538 Figure 1. Study area and position of marine caves studied. GR = Gorgonias; CN = 539 Cantarriján; TM = Treinta Metros; RM = Raja Mona; PV = Punta del Vapor; CL = 540 Calahonda. 541 542 Figure 2. Percentage (%) of crustaceans groups inside caves, outside caves and all 543 study, calculated in function of number of species (a) and number of individuals (b). 544 545 Figure 3. Two-dimensional MDS plot for species composition. Data were four rooth 546 transformed. Dashed lines grouped stations with similarities over to 40%. Continuous 547 lines grouped stations with similarities over to 60%. 548 549 21 Figure 4. Mean values ± SD of diversity, number of species and number of individuals 550 m-2 for each sampling station. Significance of differences between positions was also 551 represented. ** = p < 0,01; n.s. = Non significant. GR = Gorgonias; CN = Cantarriján; 552 TM = Treinta Metros; RM = Raja Mona; PV = Punta del Vapor; CL = Calahonda. 553 554 Figure 5. Similarity values (Bray-Curtis index) between replicates within each station. 555 GR = Gorgonias; CN = Cantarriján; TM = Treinta Metros; RM = Raja Mona; PV = 556 Punta del Vapor; CL = Calahonda. 557 558 Figure 6. Results of PCA for physico-chemical variables of the sediment. 559 560 561 562 22 563 564 23 565 24 566 567 568