Lillis, A.; Snelgrove, P.V.R. (2010). Near-bottom hydrodynamic effects on postlarval settlement in the American lobster Homarus americanus. Marine Ecology-progress Series. 410 161-172.
Following a planktonic larval phase, American lobster Homarus americanus postlarvae seek out appropriate habitat in which to settle and develop through a shelter-restricted juvenile phase. Previous studies have shown that lobster postlarvae exhibit strong directional swimming ability, distinct bottom-searching behaviours, and clear responses to physical and chemical cues at settlement. However, most laboratory experiments have been conducted in still water and little is known about how hydrodynamics affect lobster settlement. We conducted flume experiments with different sizes of cobble to investigate the effect of moderate flow (similar to 7.5 cm s(-1) free stream velocity) on postlarval swimming behaviour and settlement. In 1 h trials, significantly more postlarvae settled in flow than in still water. Post larvae in flow were more likely to encounter bottom substrate than postlarvae in still water. Cobble size had no significant effect on settlement. Behavioural observations indicated that postlarval behaviour is modified by flow. In contrast to still water, postlarvae in flow appeared to deliberately sink and were entrained by bottom turbulence, thereby contributing to higher substrate encounter and settlement rates. Post larvae in flow performed significantly fewer dives and exhibited fewer bottom searching behaviours than postlarvae in still water. Bottom flow therefore affects settlement frequency by influencing encounter rates through an interaction between passive and active processes. These results suggest that lobster settlement behaviour may be affected by spatial and temporal differences in flow and should therefore be considered when examining and predicting settlement patterns.