The dispersal of tropical coral reef fish larvae: Genetic markers, planktonic duration and behavior

The majority of coral reef fishes possess an early planktonic larval phase. The possession of this planktonic phase has led to the assumption that reef fish populations are mainly replenished by outside sources. Ichthyoplankton surveys, biogeographic analyses and population genetic studies largely supported this assumption. The importance of local recruitment, however, has never been explored as a mechanism in replenishing these populations. This study used the sequence variation of the mtDNA control region to determine the degree of larval dispersal in a local population of the rabbitfish Siganus fuscescens in the northwestern Philippines. It was hypothesized that this reef fish could be maintained by self-recruitment since it lays demersal eggs. The phylogenetic analysis and the analysis of molecular variance of the control region sequences of the neighboring adult populations of S. fuscescens indicated population genetic structuring that implied low larval exchange. This finding was confirmed by high relatedness of the local juvenile S. fuscescens to the local adults. A comparative analysis of the population genetic structure and the juvenile affinities of the pelagic egg spawning S. argenteus, indicated that the demersal egg type most probably led to S. fuscescens local recruitment. The short planktonic larval duration (14 days) of S. fuscescens is probably another passive mechanism for local recruitment. This planktonic larval duration is the shortest known for tropical coral reef fishes. There is also evidence that larval S. fuscescens may actively return to their natal reefs based on the field larval release experiments. These field observations provided valuable insights and possibly the first solid evidence that larval behavior can be an active mechanism for reef fish larvae to return to where they were born. Two other independent and very recent findings have also indicated recruitment through retention of locally spawned reef fish larvae. This evidence of local recruitment now points to the necessity of developing population models that relate recruitment to the local spawning populations. There is evidence that patterns of recruitment may not be completely independent of local population dynamics, as previously suggested.