Macrobenthic diversity and community structure at Cochin Port, an estuarine habitat along the southwest coast of India

Abstract

Estuarine habitats are highly dynamic owing to tidal and seasonal changes in physical and chemical properties, which, in turn, have a profound influence on the diversity and community structure of its living components. At the same time, estuaries have served as centres of maritime trade. Therefore, benthic organisms inhabiting the estuarine environment can act as bio-indicators of natural and anthropogenic changes, but our current knowledge of these components is still poor in the tropics. A study of the macrobenthos (principally comprising polychaetes), along with associated environmental variables was therefore assessed during October 2011 to November 2012 in and around Cochin port, a tropical estuarine habitat influenced by the monsoon and port-related activities. Our results showed that the diversity, abundance and community structure of the macrobenthos varied with season. Maximum diversity and abundance occurred following the southwest monsoon (post-monsoon II; November 2012), while both variables were at their minimum during the monsoon. The abundance of macrobenthos was lower in clayey-silt compared to sandy sediment. Polychaetes were the dominant organisms, followed by oligochaetes and amphipods. Sediment enrichment and seasonal changes in the sediment characteristics led to the dominance of opportunistic species such as Prionospio sp., Paraprionospio sp., Nephtys sp. and Oligochaeta observed during different seasons. Polychaete species such as Prionospio sp. (an indicator of oxygen depletion) and Cossura coasta (an indicator of sediment instability) were observed during the study. The multivariate index of trophic state (TRIX) indicated highly eutrophic waters and would be the main cause for the seasonal changes in the macrobenthos diversity. This study will serve as a baseline for future studies on the diversity of macrobenthos and benthic ecology of monsoon-influenced coastal habitats especially in a busy port subjected to severe physical and anthropogenic stress.