Influences of predators and conspecifics on recruitment of a tropical and a temperate reef fish

An active debate has focused on whether patterns in the abundance of reef fishes are primarily determined by the supply of larvae or by subsequent interactions occurring on the reef. By manipulating the presence of predators and the density of older conspecifics on small standardized reefs, we tested the influences of these 2 factors - and interactions between them - on recruitment of reef fishes. To assess the generality of our findings, we conducted similar experiments on 2 closely related species in 2 different systems: 1 tropical and 1 temperate. At Santa Catalina Island (a temperate site in southern California, USA) we worked with the blackeye qoby Coryphopterus nicholsii and at Lee Stocking Island (a tropical site in the Bahamas) we studied the bridled goby Coryphopterus glaucofraenum. Predators reduced recruitment of blackeye gobies, but in contrast, in one experiment, recruitment of bridled gobies was positively affected by 1 class of predators (reef residents) and unaffected by transient predators. In another experiment, recruitment of bridled gobies was unaffected by either class of predators; however, there was little statistical power to detect a similar positive effect of predators. Older conspecifics (adults and subadults) did not significantly influence recruitment of blackeye gobies, but recruitment of bridled gobies was negatively related to density of adult conspecifics. For both species, the presence of predators did not influence the relationship between recruitment and the density of older conspecifics. Our results suggest that patterns of abundance among local populations of reef fishes can be decoupled from patterns of larval supply by reef-based biotic processes (namely predation and intraspecific interactions). However, the influences of older conspecifics and predators varied widely between the 2 quite similar species that we studied. This underscores the need to understand the specific reasons for such differences in order to make predictions regarding the relative importance of these processes in novel circumstances.