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

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.