Temporal variability in copepod gut pigments over the central western continental shelf of India

Abstract

The Indian Western continental shelf (IWCS) is amongst the most productive regions of the world, being noteworthy for upwelling (south-west monsoon) and downwelling (north-east monsoon) that tunes the water biogeochemistry. The present study provides baseline information on temporal variation of in situ copepod gut pigments from IWCS. The copepods were collected between November 2011 and October 2013 and gut pigment contents and composition were estimated using the gut fluorescence method. Results revealed that copepods procured high gut pigment content in monsoon that coincided with ambient water pigment credited to discrete upwelling. Fluorometric analyses of copepod orders revealed presence of gut chlorophyll a (Chl a) throughout the study with highest gut Chl a (0.31 ± 0.25 ng copepod−1; N = 21) and total gut pigments (2.01 ± 2.15 ng copepod−1; N = 21) recorded in Calanoida. Consecutively, Calanoida and Poecilostomatoida chiefly consumed autotrophic biomass that was evident from presence of canthaxanthin and astaxanthin as dominant gut pigments. Interestingly, the marker pigment of Cryptophyceae was present only in Calanoida during monsoon and post-monsoon. Collectively these results conclude that copepods predominantly showed omnivory with discrete temporal variability by grazing upon autotrophic biomass that in turn probably supports the fishery.