Surface cyclopoid copepod assemblages in relation to environmental conditions near undisturbed coral reefs of Minicoy, southeastern Arabian Sea, a part of the Indian Ocean

Abstract

The cruise conducted in the spring inter-monsoon (pre-monsoon) of April 2015 in the frame of a funded project epitomized an open ocean survey that allowed procuring a quasi-synoptic picture of cyclopoid copepod community structure in 18 open ocean stations of the Minicoy Island, Lakshadweep archipelago, off the southwestern Indian coast, based on the analysis of standing stock and composition in the integrated 0-10 m water column. The main objective was to explore the community structure of cyclopoid copepods prevailing here and which environmental variable influences the same. It is witnessed that sea surface temperature (SST) (30.42 ± 0.19°C), sea surface salinity (SSS) (33.56 ± 1.15 psu), and dissolved oxygen (DO) (4.32 ± 0.06 ml/L) with SSS and DO are the best matching variables diversifying cyclopoid copepod species (av. abundance 700 ± 386 no. of individuals/100 m 3). Average zooplankton biomass (0.03 ml/m 3) and abundance (8,989 ± 3,866 no. of individuals/100 m 3) were also observed. Fifty-one cyclopoid copepod species belonging to four families and seven genera were identified, with the dominance of high saline species such as Sapphirina, Copilia, Farranula, and Oncaea. An abundance biomass curve (ABC) plot analysis indicated an undisturbed community with normal environmental conditions. TAXDTEST (taxonomic distinctness) depicted a diverse condition where all points clustered together within a 95% confidence level. Our results indicate that the cyclopoid copepod assemblage near Minicoy Island is a diverse, undisturbed community and hypothesize that the stable environmental conditions during pre-monsoon (spring inter-monsoon) preferred the diversification of cyclopoid copepods with the prevalence of high saline species. The data evolved could be used as a standard reference/benchmark to detect any deviation from an undisturbed/diverse community status of Minicoy Island in the looming scenario of climate change in and around the Indian Ocean.

Environmental DNA captures diurnal fluctuations of surface eukaryotes on a tropical coral reef

“…When applying molecular methods to assess the abundance of planktonic organisms, such as copepods and dinoflagellates, a consideration of the source of genetic material is also required. Reported densities of zooplankton and phytoplankton at similar Indian Ocean sites vary significantly, with estimates of up to 50 × 10 6 and 15 × 10 6 cells L −1 , respectively, as well as average copepod densities of 3700 individuals/100 m 3 (Radhakrishnan et al., 2020; Shaama et al., 2020; Soondur et al., 2022). With a total volume of 3 L filtered per sample, it is certain that whole microplankton would have been processed and contribute to relative read frequency recorded here.…”