Date of Award
Doctor of Philosophy (PhD)
Oceanography and Coastal Sciences
James H. Power
Field studies were conducted to characterize flow fields and their effect on larval transport and retention within Barataria Bay, Louisiana. Drifter tracking and passive larval sampling was conducted monthly during the spring and summer months from 1994 through 1996. Fifteen drifter tracking sessions were conducted over full tidal cycles (diurnal). Drifter positions were determined approximately every thirty minutes using a GPS receiver. A spline interpolation was used to estimate drifter positions at synchronous five-minute intervals. An analytical methodology of Okubo and coworkers was used to compute deformations; and changes in patch variances from the drifter positions. Mean tidal advection and current speeds for each tracking session were also calculated. Blue crab (Callinectes sapidus) was selected as a model species and artificial substrates were used to sample blue crab megalopae during tracking sessions and at three fixed locations within Barataria Bay. Maximum advection during a tidal phase exceeded 9,400 m. Tides appear to be the most important factor in larval advection, but wind forcing appears to be important in altering the direction of advection and the encounter rates with the shoreline. Coastal topography and bathymetry also altered the direction of tidal advection and increased deformation rates. Passive larvae within 3 km of the tidal passes at the start of an ebb tide are at risk of exportation to the Gulf of Mexico. Maximum current speeds were 8--33 cm s -1 in the upper embayments, and 16--41 cm s-1 in the main section of Barataria Bay. The order of magnitude was 10-5--10-4 s-1 for mean horizontal divergence and mean stretching deformation; 10 -7--10-4 s-1 for mean shearing deformation rates; and 10-6--10 -4 s-1 for mean relative vorticity. Mean increases in the patch variances were <1--4 m per five-minute time interval. Most blue crab megalopal settlement occurred in July and August in low and intermediate salinities. Settlement was episodic in both time and space with over 85% of the settlement at fixed sampling sites occurring in only 30% of the sampling time and at only one site, and 79% of the settlement during tracking sessions occurring in just a single tracking session.
Schaefer, Terry L., "A Drifter Study of Advection, Deformations, and Patch Variances With Application to Larval Transport and Dispersal in Barataria Bay, Louisiana." (2001). LSU Historical Dissertations and Theses. 248.