Community structure of macrobenthos in Ponnani estuary, South India with reference to occurrence of invasive alien species

Benthic organisms have been studied in past to assess the health of an aquatic ecosystem. Moreover, being sedentary forms they have been used as indicator organisms. In the present study, an attempt has been made to study the distribution and assemblage of major macrobenthic forms occurring in Ponnani estuary. A total of 23 genera of benthic invertebrate fauna belonging to 6 groups viz., Polychaetes, Bivalve, Gastropod, Amphipod, Isopod and Tanaidacian were recorded during the study. Faunistic study revealed that in high saline regions of the estuary (Veliyancode), a very good macrobenthic biodiversity was present. Bivalves were the major group enumerated from Veliyancode and Ponnani (39% and 35%, respectively), while in Biyyam predominance of gastropods (37%) were observed. Among the bivalve groups, presence of Maculista senhousia and Pholas candida, both considered as invasive species was noteworthy. Another interesting observation was the presence of Amphipod Melita zeylanica, another alien species evenly represented in all the three stations, indicating that the species had well established in Ponnani estuary. The present study is the first description of benthic organism assemblages inhabiting in the region. Results indicate that salinity is a major parameter that governs the diversity, occurrence, abundance and distribution of macrobenthos in Ponnani estuary. It also elucidates that any perturbance in the physico-chemical nature of the estuary favours the invasiveness of alien macrobenthic species in Ponnani backwaters.