Pelagic decapods in the northern Benguela upwelling system: Distribution, ecophysiology and contribution to active carbon flux

Abstract: Decapods were sampled with a 1m2 MOCNESS (mainly upper 1000m) in the northern Benguela Current during three cruises in December 2009, September/October 2010 and February 2011. Although pelagic decapods are abundant members of the micronekton community, information about their ecophysiology is very limited. Species-specific regional distribution limits were detected for various decapod species (e.g. Plesionika carinata, Sergestes arcticus, Pasiphaea semispinosa). Significant diel vertical migration patterns were determined for three caridean and three penaeiodean species. Biomass was variable and ranged from 23 to 2770mg dry mass m−2 with highest values for P. semispinosa. Fatty acid and stable isotope analyses revealed that the examined decapod species are omnivorous to carnivorous except for the herbivorous to omnivorous species P. carinata. Calanid copepods such as Calanoides carinatus were identified as an important prey item especially for caridean species. Community consumption rates of pelagic decapods derived from respiration rates ranged from 7mgCm−2 d−1 (23°S) to >20mgCm−2 d−1 (19°S, 17°S). A potential active respiratory carbon flux was calculated for migrating pelagic decapods with 4.4mgCm−2 d−1 for the upper 200m and with 2.6mgCm−2 d−1 from the base of the euphotic zone to a depth of 600m. Overall, pelagic decapods apparently play a more prominent role in the northern Benguela Current ecosystem than previously assumed and may exert a substantial predation impact on calanid copepods (up to 13%d−1 of standing stock). [Copyright &y& Elsevier]