Environmental influences on larval duration,growth and magnitude of settlement of a coral reef fish

The influence of environmental variables on the planktonic growth, pelagic larval duration and settlement magnitude was examined for the coral reef surgeonfish Acanthurus chirurgus. Newly settled fish were collected daily from patch reefs in the San Blas Archipelago, Caribbean Panama for 3.5 years. Environmental influences on growth were examined at three different life history stages: from 0 to 6 days, 7 to 25 days and from 26 to 50 days after hatching. Larval growth was correlated, using multiple regression techniques, with a combination of factors including solar radiation, rainfall, and along-shore winds. Depending on the life history stage, these accounted for 13–38% of the variation in growth rates when all the months were included in the analyses. Correlations between environmental variables and growth also varied among seasons and were stronger in the dry than in the wet season. During the dry season solar radiation, rainfall and along-shore winds described 57%, 86% and 74% of the variability in growth between 0 and 6 days, 7 and 25 days and 26 and 50 days, respectively. During the wet season rainfall, along-shore winds and temperature only described 38% of the variability in early growth and 27% of growth just before settlement. No significant model was found to describe growth 7–25 days after hatching during the wet season. Rainfall, solar radiation and along-shore winds were negatively correlated with growth up to 25 days after hatching but positively correlated as larvae approached settlement at a mean age of 52 days. Over 65% of the variability in pelagic larval duration was accounted for by a regression model that included solar radiation and along-shore winds. When data sets from wet and dry seasons were analysed separately, along-shore winds accounted for 67% of the change in larval duration in the dry season, and solar radiation accounted for 23% of the variation in larval duration in the wet season. Only 22% of the variability in settlement intensity could be described by solar radiation and temperature, when all months of the year were included in the analysis. Solar radiation and rainfall were included in a regression model that accounted for 40% of the variation in numbers of fish settling during the dry season. This study suggests that the levels of solar radiation, along-shore winds and rainfall during the early larval life can have important effects on the growth, larval duration and consequently, the settlement magnitude of marine fishes. Results also highlight the need to account for seasonality and ontogeny in studies of environmental influences.Communicated by G.F. Humphrey, Sydney