What Controls Tropical Reef Fish Populations: Recruitment or Benthic Mortality? An Example in the Caribbean Reef Fish \u3cem\u3eHaemulon flavolineatum\u3c/em\u3e

Recruitment from a planktonic larval stage has been proposed to be an important factor in limiting populations of marine organisms, particularly tropical reef fishes. We monitored recruitment and population densities of juvenile size classes In French grunt Haemulon flavolineatum (Haemulidae) from October 1978 through December 1980 In a portion of Tague Bay, St. Croix, U. S. Virgin Islands. Within our study area, 95 % of new recruits settled onto the sand and seagrass lagoon floor and within a few weeks migrated to nearby reefs; the remaining 5\u2710 settled directly onto reef structures. Mean annual recruitment rate was 1.8 recruits per m2 of lagoon floor, equivalent to 44 recruits per m2 of juvenlle (backreef) habitat per yr and among the highest recruitment rates yet reported for reef fishes. Post-settlement mortality was also very high. during the first month of benthic life it was 0.9 and during the first year was \u3e 0.992. We propose a sensitivity analysis criterion for determining the relative influence of multiple factors or processes that limit adult population size The criterion we used is the relative sensitivity of adult population size to proportionate changes in those factors or processes. Using an open, density-independent model of benthic population dynamics for French grunts, we estimate that changes In post-recruitment mortality rate will have a 100 times greater effect on the abundance of large juveniles than a proportionate change In recruitment rate Therefore we conclude that, whether or not mortality is density-independent, the factors controlling benthic mortality are much more Important in the benthic population dynamics of French grunts than is the recruitment rate. The same analysis is applied to other coral reef fishes for which appropriate data are available; we conclude that for 2 out of 3 species for which recruitment limitation has been demonstrated, changes in benthic mortality are likely to have a stronger influence on adult population sizes than are proportionately equivalent changes in recruitment rate