Distribution and abundance of benthic macroorganisms in and around Visakhapatnam Harbour on the east coast of India

Benthic communities form an important component of the marine food chain. Their occurrence also provides information on the health of the ecosystem. A study was carried out to understand the distribution and abundance of macrobenthos along with sediment characteristics and physicochemical parameters in Visakhapatnam harbour, a major port along the east coast of India. In all 84 macrobenthic taxa were reported from the port area of which 60 were polychaetes and 24 were other invertebrate taxa. Our observations revealed an increase in the number of polychaete species observed over the last 20 years from this region. An earlier study reported 38 polychaete species in 1975 and a year later the number of polychaete species reported were 12, indicating an increase in the number of polychaete species in the present study to about 150%. The macrobenthic abundance and dominance of species varied with the seasons. Pre-monsoon was dominated by Cirratulus sp., during monsoon tanaids were dominant indicating a seasonal shift in the occurrence and dominance of macrobenthos. During post-monsoon, Cossura coasta was dominant followed by Nephtys dibranchis and amphipods. Sediment characteristics (sand, silt and clay), organic carbon and dissolved oxygen were the important factors to influence the abundance and species diversity. The abundance of macrobenthic forms also varied with inner and outer harbour region. Higher species diversity was observed in the outer harbour suggesting outer harbour to have semi-polluted conditions such as higher dissolved oxygen (DO) and salinity, low nutrients (nitrite, nitrate and silicate), and low organic carbon of the sediment.