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theses

The Atlantic surfclam, Spisula solidissima, is one of the most commercially important species along the Northeast U.S. coast. Similar to many other benthic invertebrates, surfclam life history includes a dispersive larval stage. Larval dispersal plays a key role in determining connectivity among geographically distinct populations, and is further influenced by physical dynamics and larval behavior. In this graduate work, a coupled modeling system combining a physical circulation model of the Middle Atlantic Bight (MAB), Georges Bank (GBK) and the Gulf of Maine (GoM), and an individual-based surfclam larval model has been implemented to study surfclam larval transport pathways, inter-population connectivity patterns, as well as the associated physical mechanisms. Model results show a mean along-shore connectivity pattern from the northeast to the southwest among the surfclam populations. High-frequency (periods of 2~10 days) variation in larval along-shore drift is found to be due to along-shore surface wind stress variation, with the seasonal variation speculated to be driven mainly by changes in the across-shelf density gradient. Surfclam across-shelf larval movement is also highly correlated with the along-shore surface wind stress as mediated by coastal upwelling and downwelling episodes. This correlation is further dependent on larval vertical distribution with respect to the thermocline, which is a direct result of the mutual interaction of the physical environment and larval behavior. Water temperature is found to play a dominant role in larval settlement patterns. In the vertically integrated time-mean heat balance regulating water temperature on the MAB shelf, surface air-sea heat flux and horizontal heat advection are the two most important terms. Seasonal variation of water temperature is mainly controlled by the seasonally varying surface heat fluxes. Across-shore horizontal heat advection variations associated with different coastal across-shore circulation patterns contribute water temperature variations on shorter time scales from days to weeks. The long-term (e.g., decadal or longer) variation of water temperature is likely due to the variation of along-shore heat advection from the mean along-shore barotropic current acting on the mean along-shore temperature gradient, related to the large-scale coastal current system running from Labrador in the north to Cape Hatteras in the south.

ETD_5985

Ph.D.

Includes bibliographical references

by Xinzhong Zhang

doi:10.7282/T3KD20JF

ETD doctoral

The author owns the copyright to this work.