Demographic Consequences of Variable Recruitment to Coral Reef Fish Populations: A Congeneric Comparison of Two Damselfishes
Abstract:Alternative ecological models make different predictions about the long-term influences of recruitment, mortality and density upon the demography and abundance of populations of coral reef fishes. Recent validation of protocols for aging tropical fish to year-class provided the basis for testing some of these predictions. Specifically, we assessed the influence of recruitment variability on populations by comparing age structures for two species of damselfish (Pomacentrus moluccensis and P. wardi) with long-term (9 year) recruitment records from seven coral reefs located on the southern Great Barrier Reef. Detailed comparisons are given for two reefs: Wistari, which was a high recruitment reef for P. wardi and a low recruitment reeffor P. moluccensis, and Lady Musgrave, which displayed the opposite pattern. Both species lived longer on Wistari relative to Lady Musgrave suggesting that longevity is controlled by local predator populations independent of conspecific density. On Wistari, where turnover was lower, the age structures of both species were positively correlated with the initial sizes of the corresponding year-classes (for the 9 youngest cohorts). On Lady Musgrave, clear relationships were only evident for the 4/5 most recent year-classes because of the depletion of older cohorts. Most age structures contained evidence of one or more dominant cohorts among the older age classes attributable to strong recruitment in the past. Age-specific mortality schedules varied between reefs; a linear model provided the best fit in all cases although those from Wistari had little slope and high variability relative to populations from Lady Musgrave. The mortality schedules for P. wardi contained possible evidence of compensatory responses among cohorts but these patterns were weak and ambiguous compared to the influence of temporal and spatial variability in recruitment on age structure and abundance. The latter was able to account for 90% of the variability in abundance observed across species and reefs for the full data set. These comparisons indicate that the abundances of both species were determined by variable patterns of recruitment interacting with relatively uniform and non-compensatory mortality. Consequently, coral reefs that received higher recruitment of either species simply accumulated more fish with no evidence of saturation from the highest levels observed over a 9-year period.
Document Type: Research Article
Publication date: 1994-01-01
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