Influence of algal cell concentration, salinity and body size on the filtration and ingestion rates of cultivable Indian bivalves

Abstract

The effect of varying algal cell concentration, salinity and body size on the filtration (FR) and ingestion rate (IR) of three species of cultivable Indian bivalves, (green mussel <i style="">Perna viridis</i>, the backwater oyster <i style="">Crassostrea madrasensis</i> and the shortneck clam <i style="">Paphia malabarica</i>) were investigated under laboratory conditions. Axenic cultures of the unicellular alga <i style="">Isochrysis galbana</i> were used in the test solutions. The filtration and ingestion capacities of the different species in the order of high to low was <i style="">Crassostrea</i> > <i style="">Perna </i>> <i style="">Paphia</i>. The differences in the FR and IR have been attributed to the epifaunal habitat of the first two species as compared to the infaunal habitat of the latter. Increasing algal cell concentrations resulted in escalating FR and IR until a threshold of 10⁵ cells.ml^-1 in the case of <i style="">Crassostrea</i> and <i style="">Perna</i> and 7.5x10⁴ in the case of <i style="">Paphia</i>. However, at this concentration all the species showed production of pseudofaeces and therefore the critical cell concentration was one step lower to the threshold level. The FR and IR were significantly higher in larger bivalves and the peak was observed at the ambient natural salinities of the respective species tested.