Typically, in estuarine environments inhabited by P. viridis, the salinity drops to about 20& after heavy monsoon rainfall (Rajagopal et al. 1989). The timing and duration of the reproductive cycle of mussels are believed to be controlled by an interaction of environmental and endogenous factors (Seed 1976; Sastry 1979; Kautsky 1982; Rajagopal 1991). Barnes (1957) has
shown that synchronization of spawning in marine epibenthic communities is particularly tuned to the main phytoplankton blooms and only indirectly to temperature. Kautsky (1982) reported that food availability is the primary controlling factor for gonad growth in Baltic M. edulis. Relatively stable environments may promote year-round spawning, with a couple of identifiable peaks (Parulekar et al. 1982; Walter 1982). For example, in tropical waters of the Bay of Bengal, Rajagopal et al. (1998a, b) reported two spawning peaks. In subtropical environments the spawning is restricted to warmer months (Shafee 1989).