9415601 Madin The goal of this project is to determine the abundance and distribution of macrozooplankton and fishes in the Arabia Sea, and to estimate their contribution to the vertical flux of organic matter in these environments. The monsoonally forced Arabian Sea ecosystem is one of the most productive in the world, but with sharp, seasonal contrasts in production and sedimentation. The system is unusual in the distribution and comparison of its fauna, and in the pathways by which surface production is distributed into the water column and sea floor. The Somali coastal upwelling zone is a productive region supporting a high-biomass, low- diversity pelagic fauna, and the equatorial Indian Ocean is a typical oligotrophic zone with a high diversity of inadequately known species. Many questions remain to be answered on the role of such processes as defecation and diel vertical migration of large organisms in regulating vertical fluxes of material in these contrasting regimes. Specific objectives of the study include: 1) determination of distribution and abundance of macrozooplankton and fishes; 2) determination of the extent and timing of diel vertical migration of zooplankton and fish; 3) examination and quantification of stomach contents and egestion rates of macrozooplankton; 4) use of trawl collections to provide ground-truth calibration of concurrent acoustic sampling by other investigators; and 5) analysis of the species diversity and zoogeography of macrozooplankton and fishes in the Arabian Sea and adjacent equatorial Indian Ocean. Our results will contribute to understanding community structure and trophic dynamics in the Arabian Sea and Indian Ocean pelagic ecosystems. The cruises will be concurrent with two of the JGOFS Pelagic Process cruises, and our data will bear on JGOFS objectives of measuring and understanding vertical fluxes in the Arabian Sea.
