Local-scale Patterns of Larval Settlement in a Planktivorous Damselfish—Do They Predict Recruitment?

Abstract

The degree to which local-scale spatial variation in larval supply predicted subsequent patterns in juvenile densities was examined for a planktivorous damselfish (Dascyllus trimaculatus) at Moorea, French Polynesia. D. trimaculatus young settle from the plankton to sea anemones, where they remain until becoming free-ranging adults. Daily settlement onto anemones without fish was estimated at several sites in a lagoon for one 14-day period and compared with patterns in the density of juveniles that had accrued after 10 successive settlement periods. Spatial variation attributable to larval supply occurred mostly among individual anemones, between the halves of each study site, and among different locations in the lagoon. In contrast, there was relatively little variation at any spatial scale in the density of young after 10 settlement pulses. Several mechanisms were examined that could account for the observed reduction in spatial variance through time, and three involving interactions with young already present were implicated. First, settlement was not independent of residents (the density of young already on an anemone); compared with the absence of fish, settlement was facilitated at low and inhibited at high densities of residents. Second, older juveniles moved among local anemones, and the immigration and emigration rates per capita varied with density on an anemone. Finally, per capita mortality during the first few days after settlement was density-dependent. These findings emphasize the critical need to distinguish among effects that arise from the delivery of larvae, the availability of appropriate habitat, and interactions that affect fish at settlement and immediately thereafter.