Biogeography and Population Connectivity of Coral Reef Fishes

Most fundamentally, the distribution of populations and species is a function of both habitat availability and dispersal ability. Understanding the patterns that result from the interaction of these factors is one of the central aims of ecology. It has long been recognized that populations are not evenly distributed throughout the entire geographic range of the species. Populations occupy spatially distinct patches of suitable habitat that are separated from each other by areas of unsuitable habitat. Depending on factors such as the distance between populations, the nature of the intervening environment, and the relative mobility of the organisms in question, areas of unfavorable habitat may or may not prevent movement of individuals among patches. Given a long enough period of isolation between populations of the same species, speciation or local extinction may result. The degree of connectivity among populations therefore has major ecological and evolutionary implications. Though the implications of connectivity have long been acknowledged and explored in terrestrial organisms, variable connectivity patterns are only beginning to be recognized as an important driver of present-day population dynamics in the marine realm. It had long been assumed that, due to the lack of visible barriers and the presumed ability of larvae to passively disperse great distances by riding ocean currents, marine organisms dispersed freely and had high levels of population connectivity throughout their ranges. Recent studies in coastal habitats, however, have revealed that the larvae of many coral reef fish species actually settle much closer to their natal reefs than previously thought (Almany et al., 2007; Jones et al., 1999; Kingsford et al., 2002; Planes et al., 2001, Swearer et al., 1999; Taylor & Hellberg, 2003). Similarly, population structure has been found in pelagic species such as cod (Bentzen et al., 1996; Ruzzante et al., 2000) and tuna (Block et al., 2005; Carlsson et al., 2004). The existence of patchy marine populations, especially if the patches are not connected by migration or dispersal, has enormous implications for biodiversity conservation and management. For instance, isolated populations are more prone to extinction than are more connected ones (Munday, 2004). In this chapter we present an overview of the distribution and population connectivity patterns of coral reef fishes and the methods that have been used to quantify them. We argue that widespread variability in predicted and observed patterns can be explained via the interaction between reef fish life history traits and oceanographic conditions. We emphasize throughout the importance of understanding the