Apart from flow, settlement pattern in marine mussels is influenced by other factors such as
substratum (Rajagopal 1991; Lasiak and Barnard 1995; Rajagopal et al. 1998a, b). P. viridis selects a favourable surface prior to the secretion of byssus (Nishida et al. 2003). According to Widdows (1991), settlement-ready pediveliger larvae of mussels can delay the process of settlement and metamorphosis for several weeks until a suitable substratum is found, though such a delay may result in a decline in the number of offspring surviving. Alfaro et al. (2005) studied early settlement patterns of P. canaliculus within water tanks exposed to different water flow regimes and oxygen concentrations. Hatchery-reared larvae and wild juvenile mussels (0.5 –3.0 mm shell length) were used for the experiments. Settlement of larvae increased with increasing water flow; also higher oxygen concentrations appeared to enhance larval settlement but not in juveniles. Interestingly, the experiments suggested that exploratory behaviour
(i.e., settlement and re-settlement) takes place within low and medium water flows, but not under high water flows. This study clearly pointed to the complexity of larval and juvenile settlement and re-settlement processes in P. canaliculus. It would be interesting to investigate if similar mechanisms operate for P. viridis as well.