Spatial variability in mesozooplankton community structure in the Seychelles-Chagos Thermocline Ridge during spring intermonsoon

Abstract

The significant upwelling region known as Seychelles-Chagos Thermocline Ridge (SCTR) is formed by strong air to ocean interactions that affects the sea surface temperature and marine ecosystems. To evaluate the spatial variability in mesozooplankton community structure in the SCTR, the mesozooplankton community and related environmental factors were analyzed. Survey along the 60°E and 67°E (from 3°S to 12°S) at 7 depth layers within 0-1,000 m in the southwestern Indian Ocean was conducted during spring inter-monsoon (6-18 April, 2018) by using multiple opening/closing net and environmental sensing system (MOCNESS). The mesozooplankton community was divided into 3-4 groups (similarity 30-50%) that distinguished environmental regions in the SCTR. In the epipelagic (surface to 200m) zone of transect 60°E, upwelling indicator species of Oncaea media and copepodites of Oncaea were abundant, while foraminiferans and other cyclopoid copepods were abundant in transect 67°E. The depth layers 4 & 5, and 6 & 7 had same clustering of stations. The depth layers 4 & 5 showed distinctive clustering of stations in different transects that was distinguished by abundance of copepod nauplius, mollusk larvae, and copepodites of Scolecithrix, Oithona, and Oncaea. The depth layers 6 & 7 were distinguished by the abundance of foraminiferans, calanoid copepodites of Rhincalanus, and copepodites of Oncaea and Oithona species. The spatial variability in mesozooplankton structure showed the complexity of water column in the SCTR region during the spring inter-monsoon.