Parrotfish recruitment revisited: a key role for sea surface currents

Abstract

Despite considerable attention to the role of parrotfish assemblages in maintaining coral reef ecosystem integrity, little is known about the factors affecting parrotfish settlement, which could play an important role in structuring parrotfish assemblages. Here, I expand on a previous study that sought to identify environmental correlates of the temporal patterns of recruitment of Sparisoma parrotfishes onto standardized settlement units sampled at 52 consecutive 10-day intervals over an uninterrupted 17-month period on the west coast of Barbados (W.I.). By (1) including previously unavailable satellite-derived island-wide current speed data in the analyses and (2) using a more flexible (non-linear) analytical framework, the re-analysis increased the variance explained from 24% to 74%. Furthermore, island-wide current speed had stronger predictive power than all of the previously identified environmental correlates of Sparisoma recruitment, i.e. sea surface temperature and chlorophyll a concentration, and lunar phase, underscoring a dominant role for large-scale, transport-related physical processes in driving parrotfish settlement. Relationships between Sparisoma recruitment and the environmental correlates were better explained as non-linear functions, with a hump-shaped relationship for current speed. Most variability in current speed reflected external forcing due to the passage through Barbados of a large, slow-moving, low-salinity intrusion of South American riverine origin. Considering the high recruitment variance explained and that satellite-derived data on key environmental correlates are publicly available, prediction of temporal patterns of parrotfish settlement in Barbados might be more feasible than previously expected.