Local retention of production in marine populations: Evidence, mechanisms, and consequences

Abstract

A major unanswered question in marine ecology is the degree of connectedness between local populations. Put another way, what proportion of young arriving into a local population are products of local production? What is the source of recruits for any local population, and where do the young produced in a local population go? The answers to these questions are unknown for most widespread species with a pelagic larval phase. Proper marine management depends on knowledge in this area: the efficacy of any reserve design, for example, is highly dependent on the degree to which it is reliant on other populations for recruitment, and the degree to which it supplies other areas. Since most marine animals have a pelagic larval stage, the paradigm thus far has been to assume extensive dispersal and massive export (e.g., Thorson, 1950; Vance, 1973). In this view, connectivity is pervasive and extensive, with local populations receiving their young from the ‘larval pool’ to which most populations contribute. In such ‘open’ populations, recruitment is essentially independent of local production, and local dynamics are determined solely by recruitment and post-recruitment mortality (Warner and Hughes, 1988; Caley et al., 1996). To evaluate the appropriateness of this view, we convened a Working Group at the National Center for Ecological Analysis and Synthesis. Our goal was to examine the evidence for open vs closed marine populations from a wide variety of viewpoints. The following fields were represented: