Recruitment failure, life histories, and long-term decline of Caribbean corals

Population decline, local extinction, and recovery are profoundly influenced by variation in demography and life-history traits. In open populations, changes in patterns of recruitment may also have a major influence on the size of local populations, particularly for short-lived organisms. We examine here the demographic processes underlying a slow decline of corals on Jamaican reefs, where coral cover has decreased by fourfold over a 16-yr period. We divided the study into three approximately equal intervals (1977–1982, 1982–1987, and 1987–1993) and constructed size-based transition matrices for each of three abundant species of corals (Montastrea annularis, Agaricia agaricites, and Leptoseris cucullata) that differ substantially in life history: Montastrea is slower-growing, longer-lived, and has lower rates of recruitment than the other two species. Rates of survival, population growth (λ), and recruitment declined substantially over time for all species and the stable size structures became increasingly dominated by small colonies. Elasticity and life table response analysis showed that changes in the persistence of large colonies had the biggest impact on population growth in all species. Simulations indicated that the levels of larval recruitment required to maintain populations at 1977 levels increased sharply over time, even as the actual recruitment rate declined. Recruitment failure was much more important to A. agaricites and L. cucullata than to M. annularis, which could survive long periods with minimal larval input. Recovery of these populations will require an increase in both survival and recruitment. The likelihood of the latter will depend on the scale of larval dispersal, and on the impact of large-scale mortality of adults on stock-recruitment relationships. Differences in connectivity and life histories of corals will determine future patterns of recovery or further decline