SPAWNING AND RECRUITMENT OF THE BLUEHEAD WRASSE THALASSOMA-BIFASCIATUM IN BARBADOS, WEST-INDIES

Spawning and recruitment periodicity and post-recruitment mortality were investigated in the bluehead wrasse Thalassoma bifasciatum on fringing reefs on the west coast of Barbados by direct census and by otolith dating techniques. Spawning was seasonal, occurring primarily between January and August. Recruitment was seasonal, and was significantly correlated with spawning with time lags of 1 and 2 mo. This is consistent with the 45 d (range 33 to 64 d) larval life of T. bifasciatum, and suggests that seasonal variation in spawning is the principal factor driving seasonal variation in recruitment. Spawning frequency was higher around new and full moons (spring tides) than around first and last quarters (neap tides), but recruitment did not differ significantly with lunar phase. Daily spawning was more frequent during ebb tides than flood tides, with peak spawning occurring near the beginning of ebb tide. Surface currents on the study reefs were offshore on 96 % of the 94 occasions monitored, regardless of tidal phase. Surface currents at ebb tide were faster than at flood tide, and ebb tide currents were faster during spring tides than neap tides. The data suggest that both daily and lunar spawning cycles are influenced by daily and lunar variation in the speed of offshore currents. Population densities on all reefs had returned to pre-recruitment levels within 3 mo of the end of seasonal recruitment. Monthly mortality (% dying per month) on each study reef during the post-recruitment period was correlated with population density on that reef at the start of the month. This may suggest that post-recruitment mortality is density-dependent, but it could result from the covariance of density with age. However, the mean monthly mortality rate over the post-recruitment period on each reef was significantly correlated with recruitment strength to that reef. This suggests that post-recruitment mortality is density-dependent, and hence that post-recruitment processes influence the population dynamics of bluehead wrasse in Barbados.