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Environmental drivers of megafaunal assemblage composition and biomass distribution over mainland and insular slopes of the Balearic Basin (Western Mediterranean)

TitleEnvironmental drivers of megafaunal assemblage composition and biomass distribution over mainland and insular slopes of the Balearic Basin (Western Mediterranean)
Publication TypeArticolo su Rivista peer-reviewed
Year of Publication2013
AuthorsFanelli, E., Cartes J.E., Papiol V., and López-Pérez C.
JournalDeep-Sea Research Part I: Oceanographic Research Papers
Volume78
Pagination79-94
ISSN09670637
KeywordsAssemblage composition, Assemblage structure, Balearic Islands, Balearic Sea, Benthic megafauna, benthos, Biomass, bottom trawling, Catalonia, community composition, concentration (composition), Deep sea, Ecosystems, Energy Transfer, Environmental variables, Fish, Fisheries, Food Supply, Hydrographic conditions, isotopic composition, Majorca, marine sediment, Mediterranean Sea, Mesoscale, net primary production, prey availability, Significant differences, Spain, trophic interaction
Abstract

The influence of mesoscale physical and trophic variables on deep-sea megafauna, a scale of variation often neglected in deep-sea studies, is crucial for understanding their role in the ecosystem. Drivers of megafaunal assemblage composition and biomass distribution have been investigated in two contrasting areas of the Balearic basin in the NW Mediterranean: on the mainland slope (Catalonian coasts) and on the insular slope (North of Mallorca, Balearic Islands). An experimental bottom trawl survey was carried out during summer 2010, at stations in both sub-areas located between 450 and 2200m water depth. Environmental data were collected simultaneously: near-bottom physical parameters, and the elemental and isotopic composition of sediments. Initially, data were analysed along the whole depth gradient, and then assemblages from the two areas were compared. Analysis of the trawls showed the existence of one group associated with the upper slope (US=450-690m), another with the middle slope (MS=1000-1300m) and a third with the lower slope (LS=1400-2200m). Also, significant differences in the assemblage composition were found between mainland and insular slopes at MS. Dominance by different species was evident when the two areas were compared by SIMPER analysis. The greatest fish biomass was recorded in both areas at 1000-1300m, a zone linked to minimum temperature and maximum O2 concentration on the bottom. Near the mainland, fish assemblages were best explained (43% of total variance, DISTLM analysis) by prey availability (gelatinous zooplankton biomass). On the insular slope, trophic webs seemed less complex and were based on vertical input of surface primary production. Decapods, which reached their highest biomass values on the upper slope, were correlated with salinity and temperature in both the areas. However, while hydrographic conditions (temperature and salinity) seemed to be the most important variables over the insular slope, resource availability (gelatinous zooplankton and Calocaris macandreae) predominated and explained 59% of decapod assemblage variation over the mainland slope. Both fish and decapods were linked to net primary production recorded over the mainland 3 months before sampling, while the delay between the input of food from the surface and fish abundance was only 1 month on the insular slope. Our results suggest that trophic relationships over insular slopes probably involve a shorter food chain than over mainland slopes and one that is likely more efficient in terms of energy transfer. © 2013 Elsevier Ltd.

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URLhttps://www.scopus.com/inward/record.uri?eid=2-s2.0-84879583771&doi=10.1016%2fj.dsr.2013.04.009&partnerID=40&md5=a5745941b4ed03e6e92f4f8737de1a33
DOI10.1016/j.dsr.2013.04.009
Citation KeyFanelli201379