Recruitment and the local dynamics of open marine populations

The majority of marine populations are demographically open; their replenishment is largely or exclusively dependent on a supply of juveniles from the plankton. In spite of much recent research, no consensus has yet been reached regarding the importance of recruitment relative to other demographic processes in determining local population densities. We argue 1. that demographic theory suggests that, except under restrictive and unlikely conditions, recruitment must influence local population density to some extent. Therefore, 2. the question as to whether the size of a particular population is limited by recruitment is misguided. Finally, 3. the effect of recruitment on population size can be difficult to detect but is nonetheless real. A major weakness of most existing studies is a lack of attention to the survival of recruits over appropriate scales of time and space. Acknowledgment of the multifactorial determination of population density should guide the design of future experimental studies of the demography of open populations.