Predation in marine protected areas: Preliminary results of the effects on growth and survivorship of newly-settled coral reef fishes

Substantial attention has been paid to the implementation and efficacy of marine protected areas. As a result, data are available on the increased abundance of large piscivorous and commercially-important fishes within marine protected areas. Fewer studies have evaluated the indirect effects of this build-up, such as the influence on recruitment and survivorship, of young fishes. Higher predation pressures in marine protected areas should lead to lower post-settlement survival rates of newly recruited fishes as well as higher selective mortalities. For example, surviving recruits in these areas may exhibit traits such as faster growth rates and larger sizes-at-age than elsewhere. Due to the constraints of testing these hypotheses in marine protected areas (e.g. permit restrictions, confounding environmental variables), mesocosm tanks were constructed in order to run experimental trials in a controlled setting. Recruits of the bluehead wrasse, Thalassoma bifasciatum, were collected from the field, transplanted in natural densities to replicate experimental tanks and then subjected to three treatments-high predation or SPA (reflecting predator densities in marine protected areas), lower predation or NSP (reflecting predator densities in non-protected areas) and control treatments (CON) with no predators. Survivorship of recruits was recorded and compared among treatments to evaluate differential predatioan rates. To evaluate selective mortality, growth rates of individual recruits as recorded in otoliths) were compared between the initial population of recruits and the survivors of each treatment. Differences in post-settlement survival and selective mortality among treatments will enhance our understanding of ecological processes occurring within marine protected areas by shedding light on factors affecting successful recruitment of fishes to these areas.