RECRUITMENT LIMITATION, MORTALITY, AND POPULATION REGULATION IN OPEN SYSTEMS - A CASE-STUDY

Investigated the role of recruits in determining and regulating local population size of a sessile colonial invertebrate, Cellepora pumicosa (Bryozoa, Ascophora). Recruitment into a field population over 18mo was less than post-recruitment mortality, causing a decline from 230 to 64 colonies (6.1 to 2.3% cover). The mortality rate was density independent. Colony growth rate declined among larger individuals, which usually regressed in size (shrank) before they died. Modelling based on measured demography demonstrates that observed levels of recruitment and mortality will limit the population size to very low levels, although relatively small increases in number of recruits would yield a substantially larger population. In comparison, post-recruitment mortality would have to decrease greatly and remain density independent to achieve the same result. -from Author