Biomass, vertical distribution and community structure of mesozooplankton in the Sulu Sea and its adjacent waters

The Sulu Sea is a semi-isolated basin in which of the mesopelagic layer and below (>ca. 600 m) are homogeneous with high temperature (ca. 10 °C). The biomass, abundance, vertical distribution, and community structure of mesozooplankton in the upper 1000 m in the Sulu Sea and its adjacent Celebes and South China seas were investigated in February 2000 and November–December 2002. The total mesozooplankton biomass in the 0–1000 m water column was higher in the Sulu (19.6 g m−2) and the Celebes seas (19.7 g m−2) than in the South China Sea (15.0 g m−2). The total biomass in the mesopelagic layer (400–1000 m) was fairly constant in these seas, ranging 4.48–4.99 g m−2, and did not show significant variation. Likewise, there was no significant deviation from an exponential decrease in biomass and abundance with depth. The vertical distribution patterns of higher taxonomic groups also did not show specific patterns in the Sulu Sea compared to the other areas. Cluster analysis based on the Bray–Curtis dissimilarity indices applied to higher mesozooplankton taxa indicates several distinct communities between different depth layers, rather than between stations or sea areas. These results suggest that warm and homogeneous mesopelagic water in the Sulu Sea does not drastically influence the total mesozooplankton standing stocks, vertical distribution patterns, and the community structure at the higher taxonomic levels compared with those in its adjacent seas. However, the composition of copepods from the 2000 cruise indicates marked differences in the composition of calanoid families between the Sulu and Celebes seas, with dominance of Eucalanidae, Metridinidae, and Lucicutiidae in the layer of lower dissolved oxygen in the Sulu Sea, suggesting difference in community structure at lower taxonomic levels (genera and/or species) between these areas.