Distribution, abundance, and feeding ecology of decapods in the Arabian Sea, with implications for vertical flux

Macrozooplankton and micronekton samples were collected on two cruises in t he Arabian Sea conducted during the Spring Intermonsoon period (May) and th e SW Monsoon period (August) of 1995. Discrete depth samples were collected down to depths of 1000-1500 m. Quantitative gut content analyses were perf ormed on four species of decapod shrimps, Gennadas sordidus, Sergia filictu m, Sergia creber, and Eupasiphae gilesii, as well as on the pelagic crab Ch arybdis smithii. Of the shrimps, only S. filictum and S. creber increased s ignificantly in abundance between the Spring Intermonsoon and SW Monsoon se asons. These four species were found at all depths sampled, and most did no t appear to be strong vertical migrators. G. sordidus and S. filictum did a ppear to spread upward at night, especially during the SW Monsoon, but this movement did not include the entire population. S. creber showed signs of diel vertical migration only in some areas. All four shrimp species except, to some degree, S. creber lived almost exclusively within the oxygen minim um zone(150-1000 m), and are likely to have respiratory adaptations that al low them to persist under such conditions. Feeding occurred at all depths t hroughout these species' ranges, but only modest feeding occurred in the su rface layer (0-150 m). G. sordidus appeared to feed continuously throughout the day and night, Estimated contribution of fecal material to vertical fl ux ranged from < 0.01-2.1% of particulate flux at 1000 m for the shrimps an d 1.8-3.0% for C. smithii. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.