Date of Award

Summer 8-19-2022

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography

Advisor

Huijie Xue

Second Committee Member

Andrew C. Thomas

Third Committee Member

Neal R. Pettigrew

Additional Committee Members

Philip O. Yund

Ron J. Etter

Abstract

Sections of the coastal Gulf of Maine (GoME) differ in circulation, temperature, salinity, and primary production. These regional differences as well as their temporal changes, together with biological factors, such as the vertical migration, pelagic larval duration, etc., determine marine larval transports, and further affect the population connectivity, and community assembly in the intertidal GoME. To investigate the variations of coastal currents in the GoME, we built a high-resolution circulation model covering the shelf seas from Long Island Sound to the Gulf of St. Lawrence, This model was quantitatively validated with observed sea surface height (SSH), time series of temperature, salinity, and velocity, composite temperature and salinity characteristics from CTD stations, and ADCP transects. Overall, the circulation model successfully reproduced the seasonal and interannual variations of SSH, temperature, salinity, and velocity in the nearshore and coastal GoME, while the performance in predicting velocity in the offshore GoME was less successful. To study the alongshore and cross-shore material transport and population connectivity of Mytilus edulis, we evaluated a particle tracking model with satellite-tracked drifters. It can reproduce the general patterns of drifter tracks in the coastal GoME within the period of a month, though the separation distances between drifters and simulated particles generally accumulate by 3km/day. Our model showed that in the northeast corner of the GoME, the Eastern Maine Coastal Current (EMCC) possesses two cores, an offshore and a nearshore core that peak in summer and spring, respectively. The two cores can be traced back to outflows from the Bay of Fundy along both sides of the Grand Manan Island. The two cores gradually merge as flowing southwestward, but split into two branches again east of Mount Desert Rock, where the nearshore branch flows along the coast to feed the Western Maine Coastal Current (WMCC) (i.e., the connectivity between the EMCC and the WMCC), while the offshore branch turns southward to recirculate in the eastern GoME. The offshore veering occurs further northeastward in late winter and summer, but gradually shifts southwestward from summer to winter. The connectivity between the EMCC and the WMCC generally peaks twice annually, with the highest connectivity in winter and then a secondary peak in late spring or early summer. The WMCC is generally southwestward with an offshore and a nearshore core, fed by the extension of the EMCC and runoff from the Penobscot and Kennebec-Androscoggin Rivers, respectively. A sea level dome can form offshore of Casco Bay during late fall and early winter in some years associated with the northeastward alongshore wind, resulting in the northeastward flows (i.e., the counter-WMCC) on the inshore side of the dome. Diagnosis of momentum balance demonstrates that the EMCC is primarily driven by the offshore pressure gradient force (PG), while both the WMCC and counter-WMCC in late fall and early winter are mainly driven by PG and wind. The general dispersal patterns in the nearshore and coastal GoME consist of relatively uniform grounding along the coast, alongshore transport to the western GoME by the coastal currents and offshore transport to the interior gulf by the wind-driven surface current. Alongshore transport generally follows three prototypical steps: offshore dispersal along with sinking, alongshore transport, and onshore dispersal along with surfacing. Transports to the interior GoME occur prominently offshore of Penobscot Bay and east of Cape Cod, likely due to the offshore veering of EMCC, and variations of isobath inclination, respectively. Inshore of 80 m isobath, the consistent cross-shore flows result in very similar cross-shore transport between years and months, while offshore of 80 m isobath, the influence of variable coastal currents gradually emerges, which alters the cross-shore transport. In the eastern GoME, dispersal of M. edulis larvae exhibits three prototypical patterns: self-seeding, exchanges among beds in the same and neighboring bays, and southwestward alongshore transport. Self-seeding and exchange result in two settlement clusters, in Frenchman Bay and Pleasant-Western Bay, while additional alongshore transport originates in further eastern spawning beds and occurs via the EMCC. Spawning beds that produce a large amount of larvae can modulate the settlements in other beds, and further affect the overall metapopulation. Higher temperature can result in more self-seeding and exchanges among beds in the same and neighboring bays. Moreover, Passamaquoddy Bay, Blue Hill Bay and Penobscot Bay may also contribute to the M. edulis population in the eastern GoME.

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