Observation on the community structure of brown mussel Perna indica from the intertidal rocky shores of Vizhinjam, southwest coast of India

The percentage occurrence by weight of the brown mussel as Perna indica well as the various associated organisms in the community from an intertidal rocky habitat of Vizhinjam for the various months is estimated. The associated organisms on the mussel ccmmunity include, algae, sponges, sea anemones, planarians, polychaetes, sipunculids, amphipods, isopods, cirriped, crabs and gastropods. The percentage biomass of associated organisms range from 2 to 12.29 in the mussel community in various months. Cirriped form the most dominant biofouling organism on mussel. The community starts establishing on the onset of SW monsoon. A clear or distinct succession of associated organisms on the mussel was not observed in various months or season, though the biomass was found to fluctuate without any aistinct trend, in various months. The population of mussel is multimodal in size. The length ranges from 2 mm to 54 mm in a population of nearly one year old. The rate of growth of mussel in the intertidal area is estimated to be 5 mm in the first few months and 4 mm per month in the latter part of the first year. The mortality rate is not estimated though assumed to be of high order judging from the presence of dead attached shells among the living ones. Some modes remain without registering any growth for a period. In the present study the estimated grovrth rate is only for one year since second year population could not be analysed due to total exploitation of the community from the site of collection by local people. It was observed that wherever, there is a profuse settlement of Cellana radiata, Balanus amphitrite or thick algal growth on the rocks the mussel was virtually absent or scarcely populated. However Balanus amphitrit coula establish on mussel very successfully. The influence of pre-existing population of Cellana radiata and B. triteamphi on the settlement of brown mussel spat is not ascertained. Rocks on the lower intertidal zones have denser population of mussels than on upper ones that are subjected to more prolonged exposure at low tides