Influence of river discharge on zooplankton diet in the Godavari estuary (Bay of Bengal, Indian Ocean)

Abstract

In estuaries, detrital (i.e., non-living) organic matter (OM) contributes significantly to the particulate organic matter (POM) pool and we hypothesize that it may be a major source of estuarine zooplankton diet. To test this hypothesis, the isotopic composition of carbon (d13C) and nitrogen (d15N) of phytoplankton, zooplankton, and POM was assessed in the Godavari estuary (Bay of Bengal, Indian Ocean) during wet (November) and dry periods (January). As a result of higher riverine discharge, POM concentrations and values of the C/Chl-a ratio during the wet period were higher than those measured during the dry one. Relatively lower δ13CPOM values were observed during wet than dry period and contrasting to that was found for δ15NPOM. Detritus from fresh water algae and C3 plants contributed significantly to the POM pool during the wet and dry period, respectively. Based on isotopic mixing model, detrital OM and phytoplankton mostly characterized the POM pools during the wet and dry periods, respectively. Accordingly, our results suggest also that the zooplankton diet was mostly supported by detrital OM during the wet period and by both phytoplankton and detrital OM during the dry one. The zooplankton trophic level (TL, 2.7) during the wet period was relatively higher than that (1.9) during the dry one, suggesting a relative higher preference for detritus than phytoplankton during the wet period. The results of this study allowed us confirming that detrital OM can significantly support zooplankton production in the Godavari estuary.

Nutrient, phytoplankton, and zooplankton variability in the Indian Ocean

“…Among key issues unexplored in regional food-web investigations are the nutritional sources and grazing pathways that sustain zooplankton stocks during different seasons. Isotope measurements have suggested, for example, that zooplankton in river-influenced areas during the SWM might derive more food value from suspended detritus than phytoplankton (Mukherjee et al, 2018). High zooplankton biomass during the SIM has also been attributed to enhanced fluxes via the microbial loop (Madhupratap et al, 1996a;Jyothibabu et al, 2008b;Anjusha et al, 2013), but the magnitudes of grazing flows from heterotrophic bacteria and dominant picophytoplankton (e.g., Brown et al, 1999Brown et al, , 2002 have not been measured for any season.…”

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

“…Zooplankton biomass in the mixed layer during SpIM in the Arabian Sea was found to be on par with the biomass during the more (primary) productive monsoons because of the microbial loop (Madhupratap et al, 1996). Mukherjee et al (2018) in a study off the coast of the Bay of Bengal found that detrital organic matter is a major source of zooplankton diet.…”