Mesozooplankton community structure in the upper 1,000 m along the western Bay of Bengal during the 2002 fall intermonsoon

Abstract

Background: Stratification, no upwelling, sediment load, and heavy cloud cover are known to limit primary production in the western Bay of Bengal. Studies on primary consumers in this area are few. Recent studies in the Bay have shown the role of cold-core eddies in enhancing the biological production. This study was carried out to provide a detailed account of variation in mesozooplankton biomass, abundance, and copepod assemblages between cold-core eddy and non-eddy regions in the western Bay. Results: In this study carried out in the western Bay during fall 2002 intermonsoon, we observed a very high zooplankton biovolume of 2.2 ml/m 3 in the mixed layer at station WB3 located within a shallow cold-core eddy. Zooplankton from 29 groups were observed during this study. Calanoid and poecilostomatoid copepods substantially contributed to the total zooplankton abundance and carbon biomass. Below the 200 m depth, there were fewer groups but higher proportion of copepods. Copepodites of calanoids were more abundant between 500 and 1,000 m at the WB3 eddy station. Invertebrate eggs made up a staggering 65% of the total collection in the 200-to 300-m stratum at WB1, a location in the other cold-core eddy. Copepod species diversity (3.39 to 4.77) and richness (2.32 to 4.84) were lower at WB3. Among 147 copepod species in 69 genera found, Oncaea venusta (17% of the total copepod abundance), Paracalanus indicus (5.4%), Lucicutia flavicornis (5.1%), and Pleuromamma indica (4.5%) were the four most dominant ones.

Spatial structuring of zooplankton communities through partitioning of habitat and resources in the Bay of Bengal during spring intermonsoon

“…During the summer monsoon 2001, Fernandes and Ramaiah (2009) listed 163 species of copepods, of which 132 represented the order Calanoida. Similar species and diversity were recorded from this region during the fall intermonsoon (Fernandes, 2008;Fernandes and Ramaiah, 2013). Li et al (2017) identified 187 zooplankton species including the most diverse copepods from the surface along 10°N in the Bay of Bengal.…”

“…The biomass below the mixed layer, especially in the central bay, was very low and so also were the numbers of zooplankton groups, which were the least during this study compared to the other seasons even as copepod distribution remained unchanged (Fernandes et al, 2008;Fernandes and Ramaiah, 2013). The larger, faster moving zooplankton such as the euphausids having capabilities to traverse greater distances (Longhurst, 1976) were present in small numbers.…”

Vertical distribution of planktonic ostracods (Halocyprididae) in the northeastern and central South China Sea: Significance of large‐sized species in deep waters

“…In contrast, there were two cold eddies that were not completely removed by the Kuroshio intrusion at the sampling site in the NESCS during March. Cold eddies were conducive to seawater stirring, allowing more nutrients to enter the ocean mixing layer, thereby promoting higher primary productivity (Fernandes & Ramaiah, 2013; Li et al, 2017; Sardessai et al, 2007). In Li et al (2017) with same sampling stations as this study, phytoplankton blooms and high Chl a were found in the centre of a cold eddy when a branch of Kuroshio Current intruded into the NESCS with a mesoscale eddy pair in March 2016 (Li et al, 2017).…”

Mesozooplankton production, grazing and respiration in the Bay of Bengal: Implications for net heterotrophy

“…Observations during the International Indian Ocean Expedition (Panikkar and Rao 1973) and those later (see Madhupratap et al 2003) highlight winter monsoon peaks in zooplankton biomass. Recently, spatial variability in zooplankton biomass, abundance and composition in the Bay during summer monsoon and fall intermonsoon seasons were reportedly attributed to mesoscale cold core eddies (Fernandes 2008;Fernandes and Ramaiah 2009;Fernandes and Ramaiah 2013).…”