Modeling the Dispersion of Eastern Oyster Larvae (\u3ci\u3eCrassostrea virginica\u3c/i\u3e) and its Effects on the Movement of Disease Resistant Genes in the Delaware Bay Estuary

This study combines several models to address two primary research questions. How does the interaction of larval biology and environmental variability determine the spatial distribution of oyster larvae in Delaware Bay? What is the role of larval dispersion in the transference of disease-resistant genes? The particle-tracking module in the Regional Ocean Modeling System (ROMS) was converted into an Individual-Based model representing Eastern oyster larvae that has growth and vertical migration. Exchange of larvae between natural oyster reefs was estimated and used in an Individual-Based genetic model that simulates the genetic structure of eastern oysters. Particles were released from a number of reefs at several times and tracked until they reached a competent settlement size (330 µm). The simulated dispersal patterns showed that oyster larvae tend to drift down-estuary during the spawning season. The net result is that mixing of oyster larvae throughout Delaware Bay is extensive. Larval success is strongly affected by variability of temperature and salinity. Low temperature and salinity increases development times, which decreases the larval success. A stronger influence in the larval success is driven by salinity. The permanent salinity gradient in the estuary maintains an along estuary gradient in larval success. Larvae released in the upper bay populations encounter lower salinity than larvae release in the middle-lower bay populations. River discharge and spring-neap tides are the main forcing of the residual circulation. salinity and stratification in the Delaware estuary, playing an important role in the larval success and dispersion. Years with low success are related to large events of river discharge within the spawning season. Large river discharge also enhances the down-estuary dispersal pattern. Larvae released during spring tides are transported down-estuary to high salinity areas increasing the larval success of upper and middle bay reefs. The dominant. inflows in the subsurface layer and over the shoals during neap tides reduced the larval success by transporting larvae to low salinity areas. Thus, neap tides could be important in sustaining upper bay populations by increasing the export of larvae from middle to upper estuary populations. Nevertheless. the low exchange rates suggest that. this mechanism by itself can not completely explain the survival of upper estuary populations. The well-mixed conditions over most of the estuary maintain larvae distributed throughout the water column and overcome the effects of larval swimming behavior. The genetics simulations show larval dispersal might be important in the movement of disease-resistant genes from high (middle-lower bay) to low (upper bay) disease-resistant populations. The transference of the resistant trait will occur in periods of 5 to 100 years. The results of this research confirm that biophysical processes influence the dispersion pattern of oyster larvae, and thereby, the pattern of recruitment and genetic dispersal throughout Delaware Bay