Larval dispersal and population connectivity in anthozoans

Concern about the future of coral reef communities, and the recognition that larval dispersal plays a key role in the resilience of populations has spurred research to determine whether populations are connected by larval exchange or instead maintained by local supply of larvae. In the process of these endeavors, the generalized belief that marine populations were well connected via larval dispersal gave way to the notion that local retention of larvae is common among many benthic species, and that patterns of population connectivity are very complex owing to the multitude of factors and scales involved in larval transport. This review synthesizes the progress in our understanding of the processes affecting dispersal and connectivity in anthozoans (primarily corals), and examines the caveats inherent to the genetic and modeling approaches used in most connectivity studies. Conclusions about the scales of larval dispersal in anthozoans are often species-specific and almost always location- specific. However, some generalities can be recognized. Extreme cases of larval philopatry are more common in brooders. Conversely, large-scale dispersal is seemingly more common in broadcast spawners where a pre-competency period and a potentially long-lived dispersal phase provides a template for more distant dispersal. In between these extremes the divide is less clear and complex patterns of connectivity are widespread between the two developmental modes. Resolving connectivity at scales relevant to demographics remains a major challenge and considerable methodological improvements are needed. Nevertheless, both genetic analyses and biophysical modeling are rapidly maturing and provide increasingly sophisticated analyses of connectivity.