Across-shelf transport of gastropod larvae in the central Bahamas: rapid responses to local wind conditions

Abstract

Surveys for veliger larvae of the large gastropods Strombus gigas and Strombus costatus were carried out in duplicate transects running offshore (0.26-5 km) from Lee Stocking Island, Exuma Cays, Bahamas. The across-shelf distribution of the larvae during the 1991 spawning season was highly variable over periods of 3-6 days. Larvae of both species are known to inhabit the upper few meters of the water column, and analysis of wind stress patterns over the study period showed that across- shelf distribution of the larvae was affected by wind forcing. Seaward (recruitment-unfavorable) transport near Lee Stocking Island was most highly correlated with wind stress toward the north- northwest (335-357°). The resultant wind stress during the study was toward 279°, suggesting that recruitment of conch to nursery grounds on the Great Bahama Bank in the Exuma Cays occurs under anomalous summer wind conditions. The correlation between the across-shelf distribution of conch veligers and wind stress was highest with extinction coefficients of 0.17-0.23 in the exponentially filtered wind stress. This indicates that larval distribution over the 5-km-long transects responded rapidly to changes in wind stress. Over 75% of the effective wind stress occurred over just 6-8 h preceding collections; therefore, short-term changes in wind stress, such as afternoon strengthening of the trade winds, may have a significant influence on across-shelf larval transport.