Demersal Assemblages on the Soft Bottoms off the Catalan-Levante Coast of the Spanish Mediterranean

Hindawi Publishing Corporation Journal of Marine Biology Volume 2011, Article ID 976396, 16 pages doi:10.1155/2011/976396 Research Article Demersal Assemblages on the Soft Bottoms off the Catalan-Levante Coast of the Spanish Mediterranean Mariano Garcı́a-Rodrı́guez,1 Pere Abelló,2 Angel Fernández,3 and Antonio Esteban3 1 Instituto Español de Oceanografı́a, Servicios Centrales, Corazón de Marı́a 8, 28002 Madrid, Spain 2 Institut de Ciències del Mar (CSIC), Passeig Marı́tim 37-49, 08003 Barcelona, Spain 3 Instituto Español de Oceanografı́a, Centro Oceanográfico de Murcia, C/ Varadero 1, San Pedro del Pinatar, 30740 Murcia, Spain Correspondence should be addressed to Mariano Garcı́a-Rodrı́guez, Received 12 May 2011; Revised 11 August 2011; Accepted 12 September 2011 Academic Editor: Jakov Dulčić Copyright © 2011 Mariano Garcı́a-Rodrı́guez et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The analysis of 255 bottom trawl samples obtained in annual experimental surveys (2007–2010) along the western Mediterranean shows the existence of five well-defined demersal assemblages that follow a depth distribution: (a) upper shelf assemblages, including two assemblages differentiated by the type of substrate (sand-muddy and terrigenous muddy bottoms); (b) a middle shelf assemblage; (c) an upper slope assemblage; (d) a middle slope assemblage. Faunally, they are dominated by fish (37% of 452 total species), followed by crustaceans (22%), molluscs (17%), echinoderms (9%), and other invertebrates (15%). The assemblages identified showed major alterations on the shelf and shelf edge and less pronounced ones on the upper and middle slope. The average diversity values were more or less high, evidencing the high species richness in the western Mediterranean. The identified assemblages may facilitate future multispecies fisheries management based on an ecosystem approach. 1. Introduction An assemblage is a group of species whose distribution in space and time overlaps in a certain area, sharing a same habitat, bathymetric range, and so forth. A species assemblage describes the collection of species making up any cooccurring community of organisms in a given habitat or fishing ground. Often, these assemblages are also called communities. In biological terms, a community is a group of interacting organisms sharing a populated environment. In the case of the demersal species, species that dwell at or near the bottom interacting among them according to their behaviour, the identification of these assemblages according to species composition, spatial distribution, and stability will allow to determine the degree of incidence of the impacts of anthropic origin, specially trawl fishing, on them. The impacts of fishing on ecosystems are diverse in nature [1–3]. Trawling cannot only cause damage to physical components of the habitats, and therefore implying a reduction in biodiversity, but also changes the community structure, species abundance, and their size structure. In summary, it can be said that in addition to the physical alteration of habitats, fishing causes a reduction in population size of both target and nontarget species, alters their demographic structure, and substantially modifies the structure and composition of communities [4–8]. Communities less impacted by trawling sustain more biogenically habitatstructured communities (e.g., more abundance of sessile suspension feeders at the less disturbed sites versus higher dominance of small invertebrates at the disturbed site) [9]. Consequently, the knowledge of the different communities inhabiting the trawled bottoms is fundamental to understand the dynamics of communities and populations and their relationships with the structure of the habitats and environmental factors, as well as the fishing impacts on them. Demersal fish communities and the depth distribution of their component species have been studied in various areas of the Mediterranean Sea, such as the Tyrrhenian Sea [10], the Ionian Sea [11], the Aegean Sea [12, 13], the Adriatic Sea [14], and the Gulf of Lions [15]. The studies referring to demersal fish communities in the Spanish Mediterranean include those of the Balearic Islands [16–18], on the shelf Journal of Marine Biology 42.5 9◦ 56 W 2 44◦ 4 N 9◦ 8◦ 7◦ 6◦ 5◦ 4◦ 3◦ 2◦ 1◦ 0◦ 1◦ 2◦ 3◦ 4◦ 44◦ 44◦ 43◦ 43◦ ◦ ◦ 42 41◦ 41.5 41◦ 40◦ 40◦ 39◦ 39◦ 38◦ 38◦ 37◦ Mediterranean Sea 37◦ 36◦ 41 42 Iberian Peninsula 4◦ 6 E 42 Cape Creus 36◦ 9◦ 8◦ 7◦ 6◦ 5◦ 4◦ 3◦ 2◦ 1◦ 0◦ 1◦ 2◦ 3◦ 4◦ 35◦ 57 N 40.5 40 39.5 39 38 Cape Palos 38.5 Mediterranean Sea 37.5 −1 −0.5 0 0.5 1 1.5 2 2.5 3 3.5 Figure 1: Location of study area and sampling points. Cumulative data from MEDITS surveys series for the period 2007–2010. and slope of Catalonia [19, 20], in the Alboran Sea [21] and in the Gulf of Alicante [22]. The species that inhabit deep zones, below 1000 m, have been studied in the Catalan Sea [23]. Crustacean communities have been studied in the Catalan Sea [24–26], elasmobranch communities in the Balearic Islands [27], and cephalopod communities both in the Balearic Islands [28] and on the Mediterranean coast of the Spanish mainland [29], while the relationships between macro-epibenthic communities and fish were studied in the Balearic Islands [30]. On the other hand, fisheries must be managed not only to optimize catches, but to attain sustainability of the resources and ecosystems. In this sense, the traditional approach, based on single stock assessment, represents an inadequate management strategy for multispecies fisheries [31]. The integrated assessment of fisheries requires studies that focus on the ecosystem as a whole rather than on a single species, and that considers fishing activities as key pressures affecting various components of the ecosystem. In this sense, the use of an ecosystem approach to fisheries management (EAFM) may provide a holistic view of the ecosystem-fisheries interactions, while trophic indicators could therefore be used to support the implementation of an EAFM by providing information on the state of the ecosystem [32]. However, studies dealing on demersal assemblages as a whole, that is, not limited to a specific community or taxocenosis but considering all the species, including fish, crustaceans, cephalopods, and other invertebrates, and thus encompassing the relationships between macro-epibenthic invertebrates and demersal fish are scarce in the western Mediterranean [33–35] as well as on the Spanish coast [30, 36, 37]. In the Spanish Mediterranean, the total trawl fleet in 2009 was composed by 797 vessels [38]. It operates mainly in local fishing grounds, although a limited number of vessels work in French waters of the Gulf of Lions. The fleet can be divided into three groups: ves (...truncated)