MEPS 124:31-42 (1995)  -  doi:10.3354/meps124031

Little is known of the sources of mortality that affect local population dynamics of coral-reef fishes. To examine the role of predation, resident piscivorous fishes [moray eels (Muraenidae), large squirrelfishes (Holocentridae), groupers (Serranidae), and snappers (Lutjanidae)] were removed from 3 of 6 isolated patch reefs of living coral near Lee Stocking Island, Bahamas, in 1992. All 6 reefs were then seeded with natural densities of newly settled recruits of 3 species: Chromis cyanea (blue chromis, Pomacentridae), Halichoeres pictus (rainbow wrasse, Labridae), and Thalassoma bifasciatum (bluehead wrasse, Labridae). Controls showed that any secondary effects of transplanting new recruits were negligible. Over the next month, survivorship of C. cyanea (mean: 41.3%) and H. pictus (80.8%) on the predator-absent reefs was significantly greater than on the predator-present (control) reefs (9.4% for C. cyanea and 43.2% for H. pictus). No statistical difference was evident for T. bitasciatum (48.5 vs 37.8% survival), perhaps because juveniles of this species are cleaner fish and/or because they were less conspicuous to predators than the other species. Although the size distributions of the wrasses did not differ between treatments, the size distribution of C. cyanea shifted significantly. At the end of the experiment, surviving C. cyanea were slightly larger on the predator-present reefs (mode = 4.0 cm total length, TL) than on the predator-absent reefs (mode = 3.5 cm TL), despite no significant difference at the start of the experiment (mode for both treatments = 3.0 cm TL). We interpret this size shift as predators differentially consuming smaller recruits and/or surviving recruits growing faster after densities were reduced by predators. Preliminary remote video monitoring of the activity of transient piscivores [mostly jacks (Carangidae)] over the experimental reefs suggested that such predators may regularly visit isolated reefs in search of prey. If so, transient predators may have accounted for the surprisingly low first-month survivorship (about 40 to 80%) of new recruits on reefs where resident predators were removed. In any case, we conclude that resident predators can substantially alter the local density and size structure of reef fishes shortly after they settle from the plankton. Because piscivores differentially affected the survivorship of different species, predation may also influence the structure of reef-fish communities by altering the relative abundances of prey species established at the time of settlement.

Coral-reef fishes . Predation . Recruitment . Size distribution . Survivorship