Monsoon influences on micronekton of the Banda Sea (Indonesia)

Abstract

Spatial and seasonal variations in abundance, biomass, composition, horizontal and vertical distribution of mesopelagic fishes and crustaceans of the eastern Banda Sea sampled by a RMT 8 during the southeast monsoon (August 1984) and northwest monsoon (February 1985) are described. Total micronekton biomass decreased by about one third from August (0.14 g C·m −2) to February (0.10 g C·m −2), less than, but in accordance with, observed differences on other trophic levels in the pelagic ecosystem. The seasonal differences in total biomass were largely due to differences in specific weight of the organisms, rather than to changes in abundance. Spatial variation in micronekton biomass was largest during the southeast monsoon, with relatively low values in the area with most upwelling, the Aru Basin. Biomass distributions differed for micronekton, zooplankton and phytoplankton, indicating that upwelling in these waters occurs spotwise both spatially and in time. During the northwest monsoon the micronekton was more uniformly distributed. The taxonomic composition of mesopelagic fish and crustaceans, studied by sorting in some major groups, did not show large differences in relative abundances. Most groups decreased from August to February, except for stomatopods and leptocephali, which increased. Differences in the adult/juvenile ratios between the seasons varied per group, but in all cases juveniles were present in both periods, suggesting a continuous reproduction with seasonal differences in intensity. The micronekton did not show seasonal changes in the vertical distribution and diel migration.