Macrobenthic fauna with special reference to the ecology and population structure of a tubicolous amphipod, Chelicorophium madrasensis (Nayar, 1950) in a tropical estuary, southwest coast of India

Abstract

The ecology and population structure of the corophid amphipod Chelicorophium madrasensis (Nayar, 1950) was studied for 1�year in the Cochin estuary (CE), a tropical monsoonal estuary along the southwest coast of India. The incidence of Chelicorophium madrasensis in CE was a new distributional record from the south-west coast of India. Among the macrobenthic population, this species contributed in substantially higher density (> 90%) and biomass at the sampling location. This species showed a statistically significant positive correlation with salinity, benthic chlorophyll a, and fine sediment texture (clay and silt). The species also exhibited a significant seasonality in population dynamics, with a marked decline during the southwest monsoon which is characterized by remarkable decline in salinity and substantial changes in the substratum stability. The sex ratio was skewed towards dominance of females throughout the year. Though C. madrasensis is a continuous breeder, its peak breeding in the CE coincided with the pre-monsoon, which is characterized by mesohaline salinity and availability of surplus food. The study also showed that the high density of C. madrasensis in turn supported the sustenance of two carnivorous isopods. This study points to the fact that a strong and intricate abiotic-biotic interaction between the flora, fauna, and physical environment contributed to higher standing crop of the amphipod C. madrasensis at the study site.