Recruitment of Coral Reef Fishes: Effects of Distribution of Predators and Shelter

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<jats:p>Factors affecting recruitment and early survivorship of juvenile coral reef fishes were studied on St. Croix, United States Virgin Islands. The faunal assemblage studied included diurnally active fishes found in the rubble/sand habitat. The most abundant members were: beaugregory (Stegastes leucostictus), foureye butterfish (Chaetodon capistratus), mahongany snapper (Lutjanus mahogoni), surgeonfishes (Acanthurus bahianus and A. chirurgus) and French grunt (Haemulon flavolineatum). During the period 1978—1981, set of experimental reefs constructed from Strombus gigas shells were built in various locations relative to a major reef. Recruitment of juveniles of almost all species in the rubble/sand fish assemblage occurred more heavily on reefs that were built 20—40 m away from the main reef (into the lagoon) than on those built at the edge of the backreef. A series of experiments revealed that this is probably due to two factors: differences in available shelter and differences in encounter rates with predators. Seagrass and algae, which provide shelter to very small juvenile fishes, are absent in a "halo" zone close to the reef due to the feeding activities of reef—associated grazers (fishes and urchins). Experiments with artificially produced halos and artificial seagrass and algae showed that part of the explanation for the observed spatial pattern of fish recruitment is the spatial pattern of the shelter provided by seagrass and algae. Experiments in which potential prey fish were tethered demonstrated that the risk of predation for small juvenile fishes was considerably higher close to the reef than it was 20 m away. The results of these experiments suggest that patterns of settlement and juvenile survivorship of coral reef fishes are affected by complex interactions with other reef organisms (in this case, he activities of reef—associated grazers that modify available shelter) and by the frequency of encounters with predators. If they survive, all of the juveniles, regardless of where they initially settle, eventually migrate to a nearby reef. The species studies here differed in the degree to which juveniles use the sea—grass/algal habitat as a refuge from predation; these differences suggest that spatial patterns of recruitment, interacting with predation, may influence both population abundances and species composition of older juveniles on the reef.</jats:p>

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  • Ecology

    Ecology 66 (3), 1056-1066, 1985-06

    Wiley

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