Structure and dynamics of food webs in the water column on shelf and slope grounds of the western Mediterranean

Inglés. Benthic–pelagic coupling is an important process connecting species throughout the water column, particularly,in deep-sea systemswhere faunal assemblages can be dense if indirectly sustained by production fromthe above.Through stable isotope analyses, this study explored the sources of production, trophic structure, and benthopelagiccoupling in two locations with contrasting oceanographic conditions from the western Mediterranean,in the Balearic (BsB) and the Algerian (AsB) sub-basins. The samples of 89 dominant species (23 decapods, 19cephalopods, 33 fishes, among the other taxa), inhabiting the hyperbenthic and pelagic domains, from theshelf break (250 m), upper slope (650 m), and middle slope (850 m) were analyzed. Results suggested longfood webs of approximately four trophic levels (TrLs) that were sustained by planktonic source material inshallowerwaters and degraded particulate organic matter of planktonic origin in deeperwaters.Most of the collectedspecies (70%) occupied intermediate trophic positions between the 3rd and 4th TrLs. The species δ15Nandδ13C values exhibited a broad range, consistent with the high diversity that might be attributed to the oligotrophicconditions. As the depth increased, stronger segregation occurred between the trophic groups, and spatialdifferenceswere found among consumers of the two locations. Species in the AsB always had consistently higherδ15N values than in the BsB, which could possibly be attributed to the basal δ15N that was present through thefoodweb. Despite the contrasting basin characteristics, a similarly close bentho-pelagic coupling pattern was observedat both locations, except at the deepest ground, especially at the AsB,where themean δ13Cvalues fromthehyperbenthic and pelagic compartments were more distant. This could be related to the higher degree ofreworking of organicmatter in the AsB. Overall, these findings suggested the need for a depth-stratified approachto analyze deep-sea food webs in the study site in future studies

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