Food consumption by bathyal decapod crustacean assemblages in the western Mediterranean: predatory impact of megafauna and the food consumption-food supply balance in a deep-water food web

14 pages, 4 figures, 4 tables

Estimates of the daily ration consumed by decapod assemblages were obtained from 2 continuous sampling cycles conducted over the middle and lower slope (610-710 m and 1178-1240 m depth respectively) of the Catalan Sea (NW Mediterranean). Annual food consumption by decapods decreased from 82.2 mg dry weight (DW) m-2 yr-1 on the middle slope to 20.4 mg DW m-2 yr-1 on the lower slope. Additionally, from literature sources, the food consumption by fishes and the secondary production of macrobenthos and macroplankton were assessed for our deep-sea area. Combining the food consumption of megafauna (decapod crustaceans plus fishes), a model of the food supply-food consumption balance was proposed for the middle slope, the only depth stratum for which adequate information exists. On the middle slope, annual food consumption by megafauna amounted to 160 mg DW m-2 yr-1 while secondary production by the dominant macrobenthic taxa (suprabenthos, epibenthos and infauna) was estimated at 150 mg DW m-2 yr-1. Benthos was the main contributor to the food supply in our megafaunal mid-slope communities. The mean annual contribution of macroplankton was secondary, although it can be seasonally important. Euphausiids were the dominant macroplankton taxon over the middle slope, and only 10.6% of their secondary production (7.3 mg DW m-2 yr-1) was estimated to be consumed by decapods, whereas the total estimated euphausiid production consumed by our mid-bathyal community hardly attained 20%. Our results showed a tight equilibrium between food consumption and food supply on the middle slope. Estimated food consumption by midslope megafauna (0.059 g C m-2 yr-1) is equivalent to calculated values for production by benthic and suprabenthic macrofauna. This value is also consistent with estimates of mid-slope organic carbon through sedimentation (1.8 g C m-2 yr-1), after correcting for metabolism by benthos (from macrofauna to sediment bacteria). These results are consistent with the commonly accepted idea that food is the main limiting factor in deep-sea trophic webs

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