Recruitment limitation is the theoretical basis for stock enhancement in marine populations

Coral reefs support great biological diversity, which has been equated with ecosystem stability and strong interactions (e.g. competition, predation) among species, making them poor candidates for stock enhancement. Sustained monitoring of reef fish dynamics and large-scale natural experiments suggest otherwise; lessons that can be extended logically to other systems. Under normal circumstances, natural variations in recruitment modify patterns of abundance and demography. Post-settlement predation provides imperfect compensation for variable replenishment, and the persistence of dominant cohorts in populations suggests that numerical density dependence is limited to juveniles. Following major disturbances that result in expanded resources, the densities of specialists show little change, apparently because of limiting larval supply. Some coral reefs have low larval supply because of poor connectivity with other spawning sources. Such units have most potential to benefit from sea ranching and they provide natural laboratories for low risk trials into stock enhancement. The broad geographical distribution of strong cohorts suggests that recruitment limitation may be a chronic condition. While this provides a theoretical basis for enhancing most reefs and, by analogy, other systems, it is not clear whether the stocking costs, particularly 'predator swamping', are affordable. Where indicated, sea ranching may be more benign ecologically when applied selectively within metapopulations than to enhance single-unit stocks.