Settling larvae of a small coral-reef fish discriminate reef features at large, but not small, spatial scales

Larval settlement of a small coral-reef fish, the bridled goby (Coryphopterus glaucofraenum), to five entire reefs over 4 yr decreased with increasing cover of hard substrate (rock and coral). Experimentally increasing rock cover on these large reefs caused a reduction in settlement that lasted 3 yr, confirming that settling coral-reef fish discriminate among sites at the mesoscale (hundreds of meters to tens of kilometers). Counterintuitively, a smallscale manipulation of rock cover and an observational study both suggest that settlers show no response to rock cover at the microscale (few to tens of meters). Habitat selection at settlement can, thus, set initial benthic population size at much larger spatial scales than previously recognized, a finding consistent with the good swimming and sensory capabilities of late-stage larvae. Most benthic marine invertebrates and fishes have a pelagic larval stage. How these larvae colonize suitable adult habitats is critical to understanding their evolution, population biology, and community dynamics (Caley et al. 1996). The rate at which larvae become established in benthic habitats, a process referred to as settlement, shows clear spatial patterns at domains ranging from centimeters to hundreds of kilometers in extent (Doherty 1991). It is well-known that settling larvae can select specific habitats at microscales, over distances from a centimeter to a meter, (review by Kingsford et al. 2002). Experiments have revealed that larvae choose sites according to a variety of physical attributes (Sale et al. 1984; Butman 1987), some of which arise from the presence of conspecifics (Knight-Jones 1953) or other species (Sale et al. 1984). Related research has identified a variety of chemical, auditory, visual, and other cues that larvae use to make these finely resolved choices about where to settle (review by Kingsford et al.