Date of Award

Summer 7-27-2018

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography

Advisor

Huijie Xue

Second Committee Member

Philip O. Yund

Third Committee Member

David W. Townsend

Additional Committee Members

Neal R. Pettigrew

Ron J. Etter

Abstract

Because many marine species have a planktonic larval phase, an understanding of population connectivity (the exchange of individuals among populations) is critical for better understanding their adult populations. However, connectivity depends on both circulation patterns and any interacting biological factors. Of particular importance to organisms originating nearshore is the amount of cross-shelf exchange, as larvae within the slower moving coastal boundary layer experience shorter dispersal distances. I investigated circulation patterns and cross-shelf exchange along the Eastern Maine coast, a region with strong tidal currents and a complex coastline bounded in the offshore direction by a faster moving coastal current. I used blue mussels (Mytilus edulis), a commonly occurring economically and ecologically important intertidal species, as a model organism to study population connectivity in this region. I created a high resolution circulation model of the eastern Maine coast with the Finite Volume Coastal

Ocean Model (FVCOM), and validated the model using spatial and temporal datasets. The model recreated observed data both spatially and temporally. The coastal current was present among all runs and moved on and off the shelf with tides and as the seasonal stratification evolved. Flow in nearshore areas tended to the southwest out of bays, was somewhat variable among months, and had two-layer flow modulated by wind. Cross-shelf exchange was spatiotemporally variable and was affected by tides and bathymetry, with flow either following bathymetric contours or being entrained nearshore in eddies along the inner edge of the coastal current. To simulate larval mussels, I coupled this circulation model with a Lagrangian particle tracking code to mimic the interaction between physical and biological factors. I saw some exchange of simulated larvae among neighboring bays and longer-distance transport following the coastal current, along with flow patterns that may have created a barrier to exchange between Canada and the Maine coast. Along-shelf transport of larvae was affected by cross-shelf exchange, with longer distance transport occurring in the coastal current. While physical factors created many of these patterns, connectivity was modulated by seasonal differences in spawning time and reproductive output. Lastly, an increase in temperature shortened larval development times and increased settlement.

Download

Included in

Oceanography Commons

Share