Temporal patterns of settlement in the temperate reef fish Paralabrax clathratus

Variation in settlement of kelp bass, Paralabrax clathratus, from the pelagic to benthic environment was monitored daily during the summer 1998 on the leeward side of Santa Catalina Island, California. Settlement collectors were placed underwater on buoy lines at 5 to 7 m depth to provide a standardized form of spatial and structural refuge for settling larvae. SCUBA divers retrieved and replaced collectors each day for 58 d and totaled the number of kelp bass settlers found. Settlement of kelp bass occurred nonrandomly around the lunar cycle, suggesting a semi-lunar pattern of settlement just after the new and full moons, with peak settlement occurring approximately 5 d after the full moon. A high, positive correlation was found between settlement and tidal amplitude, and between settlement and onshore winds. A high negative correlation was found between settlement and sea surface temperature. This indicates a strong relationship between settlement of kelp bass and high amplitude tides, drops in sea surface temperature and strong onshore winds. These results suggest that internal tidal bores were a likely means of onshore transport, because bores produce near-bottom onshore flow and are prevalent during high amplitude or spring tides, but especially, they coincide with abrupt drops in sea surface temperature. Back-calculated spawn dates of successful settlers suggested a semi-lunar pattern of spawning just after the new and full moons, with peak activity occurring near the full moon. Kelp bass that settled at spring tides were significantly younger and smaller than kelp bass that settled at neap tides, thus suggesting that settlement of kelp bass is enhanced and larval durations shortened by oceanographic features such as internal tidal bores. Therefore, behavioral or passive synchronization to the lunar and/or tidal amplitude cycles by adult kelp bass during spawning and by kelp bass larvae during settlement result in predictable peaks in daily settlement.