It is now generally accepted that the population ecology of coral reef fishes is significantly influenced by the dispersing effect of their pelagic larvae. However, the extent to which dispersal patterns of these larvae are influenced by their behavior is a highly controversial topic, and remains a critical question at the center of marine oceanographic and ecological research. This thesis examined the extent to which tropical reef fish larvae are capable of influencing their dispersal and settlement patterns by quantifying swimming performance and behavioural characteristics throughout their pelagic phase.

The first part examines the functional swimming performance of reef fish larvae focusing on factors influencing sustained ability. Results suggest that both food and swimming speed substantially influence sustained swimming capabilities. Some larval reef fishes can maintain swimming activity indefinitely given food and many reef fish families should be able to sustainably swim 2 – 3 times faster than the average current speeds reported around reefs. Previous flume-based estimates of sustained swimming appear to underestimate the potential abilities of reef fish larvae and that sustained swimming behaviour could have a greater impact on larval dispersal than previously thought. This finding is supported in the second part, which uses video techniques to obtain the first undisturbed observations of larval coral reef fish swimming behaviour. The results support experimental and in-situ evidence of high sustained swimming speeds in these larvae. However, the most striking aspect is 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 addition, the relative 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 third part examines the vertical distribution of late stage reef fish larvae using a novel light trap design enabling discrete depth sampling in the field. The largest numbers of late-stage reef fish larvae were found in the upper layers suggesting they migrate into surface waters at night, possibly as part of the settlement process. There were consistent size-specific vertical distributions among families, with larger individuals near the surface and smaller individuals in the middle of the water column, suggesting subtle differences in water column use within species. The presence of highly structured vertical distributions in late stage reef fish larvae provides evidence of differential water column use by settlement stage reef fish larvae, emphasising the potential importance of water column use in the overall dispersal and settlement strategies of reef fish larvae.

Overall, the results of this thesis show that tropical reef fish larvae are capable of exerting considerable control over their dispersal patterns during the larval phase, as well as modifying patterns of recruitment on reefs. These abilities need to be taken into consideration when constructing oceanographic models of dispersal. Furthermore, if the full potential of larvae behaviour is realised, it may be that reef fish populations of some families are maintained primarily by self-recruitment.