Contrasting life-histories, secondary production, and trophic structure ofPeracarid assemblages of the bathyal suprabenthos from the Bay of Biscay (NE Atlantic) and the Catalan Sea (NW Mediterranean)

The life-histories and the secondary production of four dominant peracarid crustaceans (the mysids Boreomysis arctica and Parapseudomma calloplura, th e amphipod Rhachotropis caeca, and the isopod ILyarachna longicornis) in ba thyal depths of the Bay of Biscay (NE Atlantic; between 383 and 420 m) and the Catalan Sea (Northwestern Mediterranean; between 389 and 1355 m) were e stablished. Both the Atlantic and the Mediterranean populations of the majo r part of the target-species had two generations/year with mean cohort-prod uction intervals (CPI) ranging from 5.5 mo for Ilyarachna longicornis to 6. 3 mo for Parapseudomma calloplura. The Hynes method showed secondary produc tion to vary in the Bay of Biscay between 0.113 mg DW m(-2) yr(-1) for I. l ongirostris and 3.069 mg DW m(-2) yr(-1) for P. calloplura, with P/B ratios between 4.57 (I. longirostris) and 7.93 (Boreomysis arctica). In the Catal an Sea, production varied between 0.286mg DW m(-2) yr(-1) for I. longirostr is and 1.096 mg DW m(-2) yr(-1) for P. calloplura, with P/B between 5.72 (I . longirostris) and 6.66 (P. calloplura). Application of two different empi ric models to the whole peracarid assemblage gave similar levels of seconda ry production in both study areas (between 29.26 and 32.14mgDWm(-2) yr(-1) in the Bay of Biscay; between 26.23 and 26.54 mgDW m(-2) yr(-1) in the Cata lan Sea). From the analysis of gut contents of 22 species the dominant spec ies in each study area were assigned to two basic trophic levels, detritus feeders and predators. Also, cumulative curves of dominance showed high div ersity (low dominance) for peracarid assemblages distributed at mid-bathyal depths (524-693 m) both in the Bay of Biscay off Arcachon and in the Catal an Sea off Barcelona. We also discuss and compare, both within and between areas, how environmental features may explain the observed diversity patter ns, the trophic structure, and the production results obtained for the supr abenthos assemblages. (C) 2001 Elsevier Science Ltd. All rights reserved.