A Study of the Temporal and Spatial Distribution of Ichthyoplankton and Post-larval Penaeids Recruiting into a Louisiana Tidal Pass

Abstract

This dissertation attempts to better understand astronomical, meteorological, and oceanographic forcing of offshore-spawned, estuarine-dependent species from continental shelf to estuarine waters through tidal passes. The vertical distribution of zoo-/ichthyoplankton within the inner continental shelf from the Louisiana Offshore Oil Platform monitoring project (1978-1995) provided an important offshore end member for the estuarine recruitment study, and is potentially useful in predicting vulnerabilities to past and future oil spills. The role that atmospheric cold front passages may have on densities and movement of zoo-/ichthyoplankton recruiting through the Bayou Tartellan tidal pass, Louisiana, were analyzed using a Generalized Additive Model. The pre-frontal phase, with dominant southern quadrant winds, leading to coastal setup, can enhance flood tides and increase larval recruitment. Post-frontal phase strong northerly winds can enhance ebb tides, which could have negative estuarine retention implications. Lateral differences across Bayou Tartellan at a bulkheaded northern edge, center channel, and a natural-sloping southern shore edge were analyzed using a Zero Inflated Negative Binomial model to determine if behaviorally-mediated, lateral movements by larger larvae could enhance estuarine recruitment/retention. During inflows, estuarine-dependent larvae generally utilized the surface of the center channel and had much lower densities towards the edges. During outflows, larger larvae were more numerous along the southern edge, where velocities were slower. Finally, otolith age and growth data for Micropogonias undulatus and Brevoortia patronus were analyzed for growth rates and microstructure differences associated with oceanographic variability along their recruitment corridors from offshore spawning grounds through the coastal boundary layer, and into the tidal pass. Growth rates from a Laird-Gompertz model for M. undulatus were similar to previous studies. Otolith microstructure suggested ingress through the coastal boundary layer/estuarine waters occurred at approximately 40 days post hatch, and had a marked effect on growth. A two-cycle, Laird-Gompertz growth model for B. patronus suggested a growth stanza at 35 days post hatch, which most likely reflects changing oceanographic conditions during transport and biological consequences of a shift in ontogenetic feeding strategy from selective particulate feeder to an omnivorous filter feeder, with a strong initial growth rate decreasing rapidly after the beginning of the transition in feeding strategy.