PREFERENTIAL SURVIVORSHIP OF BROODING CORALS IN A REGIONAL EXTINCTION

Approximately half of the Caribbean Oligocene reef coral fauna became locally extinct during the Early Miocene; roughly two thirds of the ge nera driven to local extinction still survive in the Indo-Pacific. Cor al genera with lecithotrophic larvae (brooders) preferentially survive d, over those with planktotrophic larvae (broadcasters). Among 37 gene ra for which we inferred reproductive mode, 73% of brooding genera sur vived the Oligocene/Miocene extinction events, while only 29% of the b roadcasting genera survived. The proportion of brooders to broadcaster s also increased markedly. During the late Oligocene, 47% of Caribbean reef coral genera were broadcasters, but in the middle Miocene, only 32% of the genera were broadcasters. Survivorship in Puerto Rican reef s was correlated with tolerance of cold and turbid conditions. Genera tolerant of both cold water and turbidity had much higher survival rat es than those tolerant of turbidity alone. Only 25% of the genera that could tolerate neither cold water nor turbidity survived. Most of the eurytopic genera were brooders, while most of the stenotypic genera w ere broadcasters. We present two hypotheses that may account for the p referential survivorship of brooders: the recruitment hypothesis, and the dispersal hypothesis. The recruitment hypothesis holds that broode rs survive preferentially because lecithotrophic larvae have higher re cruitment success than do planktotrophic larvae in marginal habitats, such as upwelling zones. This is supported by the correlation of brood ing and eurytopy. The dispersal hypothesis suggests that brooders surv ive preferentially because lecithotrophic larvae, which typically inhe rit zooxanthellae from the egg, have a longer larval lifespan and, hen ce, a wider potential dispersal range, than planktotrophic larvae, whi ch typically capture zooxanthellae from the water column. Biogeographi c range data, however, do not support this second hypothesis: modern I ndo-Pacific brooding and broadcasting genera have nearly identical ran ges, and many brooding species have narrower longitudinal ranges than do broadcasting species. Preferential survivorship of brooding corals contrasts sharply with survivorship patterns among molluscs during ext inction events; among molluscs, broadcasters are favored over brooders . A major increase in upwelling at the Oligocene/Miocene boundary was probably responsible for this extinction/geographic restriction event. Preferential survival of brooding and mired mode coral genera appears to be a product of their being better able to recruit and survive in marginal conditions such as upwelling zones.