Patterns and processes of brachyuran crab settlement to Caribbean coral reefs

Many workers have examined the processes influencing the recruitment of temperate marine invertebrates but comparatively little is known about their tropical counterparts. Brachyuran crustaceans are important constituents of coral reefs, yet remain largely under-studied. To examine the temporal patterns of tropical brachyuran larval abundances and postlarval settlement, we deployed 3 replicate light traps nightly for 7 mo Flay to November 1996) at Barbados, West Indies. Wind data and tidal and large-scale flow due to currents were measured concurrently. Light traps collected a total of 320 896 zoeae tall stages and families combined) and 452 741 megalopae dominated by the families: Majidae, Xanthidae, Grapsidae, and Portunidae. While overall abundances of first-stage zoeae remained continuous over the sampling interval, postlarval settlement was more variable. Using time series analysis, periodicity in the larval and postlarval abundances was identified as: first-stage zoeae, 29 d; Majidae postlarvae, 31 d; Xanthidae postlarvae, 15 d; Grapsidae postlarvae, 28 d and Portunidae postlarvae, 21 to 22 d. We analyzed temporal patterns of zoeal abundance and megalopal settlement with respect to cyclical environmental cues as well as the mean daily wind and ambient current regime. Larval abundance was associated with the first quarter moon and minimum amplitude tides, while postlarvae were generally more abundant on the third quarter moon. Majidae postlarvae were distributed over a relatively broad period of the lunar cycle, encompassing 3 peaks occurring during the quarter moons and new moon. This pattern likely results from a strong correlation between Majidae postlarval settlement and ebb tides occurring in complete darkness. Xanthidae and Grapsidae postlarval settlement occurred predominately during the third quarter moon and intermediate to minimum amplitude tides. Postlarval abundances of these families were most tightly correlated to the maximum daily tidal range. Only Portunidae postlarvae were not influenced by proximate environmental cues such as the lunar and tidal amplitude cycles. During the study, wind was nearly consistently from the northeast, while data from an offshore current meter demonstrated that the current flowed predominately toward the north. In general, patterns of larval abundance and postlarval settlement were not as closely correlated to the wind and ambient currents as to the proximate environmental cues such as hours of darkness and the tidal cycle. We propose that cyclical environmental parameters are likely important cues to coastal species living in highly dynamic physical environments.