ABUNDANCE OF POSTLARVAL CALLINECTES-SAPIDUS, PENAEUS SPP., UCA SPP., AND LIBINIA SPP. COLLECTED AT AN OUTER COASTAL SITE AND THEIR CROSS-SHELF TRANSPORT

The abundance of the megalopae of Callinectes sapidus, Uca spp., and L ibinia spp. and the post-larvae of Penaeus spp. settling on collectors hung from the end of the Army Corps of Engineers' Field Research Faci lity (FRF) pier in Duck, North Carolina, USA, was measured daily durin g the period 2 August through 3 November 1994. During this period the coastal oceanography was dominated by the effects of the winds; winds from the NE tended to generate surface onshore now and downwelling whi le those from the SW tended to generate surface offshore flow and upwe lling. If the post-larvae were transported shoreward by coastal curren ts then variations in their abundance should relate to the physical pa rameters which generate the transporting currents. Using time-series a nalysis the daily abundance of post-larvae was statistically analyzed and compared to along- and cross-shore wind stress, along- and cross-s hore current speed near the bottom (23 m) and near the surface (4 m), and temperature, salinity, and current speed measured at the end of th e FRF pier. Fourier analysis suggested that the abundance of post-larv al C. sapidus and Penaeus spp. varied on a semi-lunar cycle, e.g. 15 d . No cycles were apparent in the Fourier analysis of the abundance of Uca spp. megalopae and the megalopae of Libinia spp. varied on an 18 d cycle. Significant cross-correlations were found between the log-tran sformed daily abundance of post-larval C. sapidus and Penaeus spp. and the maximum daily tidal range, which, coupled with the Fourier analys is, suggests that peak catches of these postlarvae tended to occur at and just after the spring tides. The cross-correlation analysis sugges ts that abundance of Uca spp. megalopae was weakly related to the tide s, with peak catches tending to occur around the spring tides. No sign ificant cross-correlations were found between the abundance of Libinia spp. megalopae and the maximum daily tidal range. To test for the eff ects of the other physical variables on post-larval abundance Autoregr essive Integrated Moving Average (ARIMA) models were fitted to the bio logical and physical data, and cross-correlations were run between the residuals from these models. The analysis suggests that the abundance of C. sapidus megalopae did not vary with any of the measured physica l variables, Penaeus spp. and Uca spp. tended to be more abundant duri ng periods of onshore surface now and downwelling, while Libinia spp. megalopae tended to be more abundant during periods of offshore surfac e flow and upwelling. The results of this study suggest that post-larv al C. sapidus and Penaeus spp. were transported shoreward by tidally d riven processes, both Penaeus spp. and Uca spp. were transported shore ward by wind-driven surface currents, and Libinia spp, megalopae were transported shoreward in near-bottom waters during upwelling events.