Undisturbed swimming behaviour and nocturnal activity of coral reef fish larvae

Larval dispersal is shaped by the interaction between oceanographic processes and larval behaviour. To evaluate the potential impact of larval behaviour on this process, we quantified the undisturbed swimming speeds and nocturnal swimming activity of 5 reef fish species throughout their larval phase. We used video techniques to obtain undisturbed observations of swimming behaviour in captive bred larvae. The results conclusively demonstrate that larvae maintain relatively high swimming speeds throughout development. Speeds were consistent among 3 anemonefish species (Amphiprioninae; Amphiprion melanopus, A. percula and Premnas biaculeatus), which swam an average of 3.9 and a maximum of 8.4 body lengths (bl) s(-1). However, differences may exist among taxa in the undisturbed swimming speeds of larvae. Highest speeds were recorded in the damselfish Pomacentrus amboinensis (Pomacentridae) and the slowest speeds in the cardinalfish Sphaeramia nematoptera (Apogonidae). The results support short-duration experimental and in situ evidence of high sustained swimming speeds. However, it is striking that larvae routinely swim at such speeds without external stimuli. The proportion of time larvae spent swimming at night increased rapidly towards the end of the larval phase in all 5 species examined. In addition, the undisturbed swimming speeds of larvae were significantly greater at night than during the day. Patterns of nocturnal activity appear to relate to the active nocturnal settlement behaviour of larvae. The pattern of swimming, and speeds achieved, suggest that an active behavioural mechanism for self-recruitment is well within the capabilities of the reef fish larvae examined.