reported increased settlement of P. viridis under high flow conditions. The high settlement intensity was attributed to enhanced propagule flux rate to the substratum, because of increased water flow. High velocity would permit settlement of only those larval forms, which have the ability to withstand high shear force. Mussel larvae are capable of settling at high water velocities (Neitzel et al. 1984; Rajagopal 1997), and it is reported that at velocities as high as 3.5 m s)1, mussels could settle and colonise new surfaces (Neitzel et al. 1984). Rajagopal et al. (1998b) also studied depth-related variation in green mussel settlement (Figure 4). Plantigrades preferred intermediate depth (4 m) to near-surface (1 m) or near-bottom (7 m), which is probably related to the subtidal habitat of the mussels. Depth-wise differences in spat fall are likely if the larvae are non-uniformly distributed in the water column or alternatively, the settling larvae prefer discrete light regimes (Figure 5). However, this depth-related feature was not apparent at high flow conditions as was observed at the intake point of a power station, owing probably to turbulent water flow, which would disturb any vertical distribution of larvae or prevent the larvae from exercising their light preferences.