Circulation, Cross-Shelf Exchange, and Blue Mussel (Mytilus Edulis) Population Connectivity in a Complex, Tidally Driven System Leann M
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The University of Maine DigitalCommons@UMaine Electronic Theses and Dissertations Fogler Library Summer 7-27-2018 Circulation, Cross-Shelf Exchange, and Blue Mussel (Mytilus edulis) Population Connectivity in a Complex, Tidally Driven System LeAnn M. Conlon University of Maine, [email protected] Follow this and additional works at: https://digitalcommons.library.umaine.edu/etd Part of the Oceanography Commons Recommended Citation Conlon, LeAnn M., "Circulation, Cross-Shelf Exchange, and Blue Mussel (Mytilus edulis) Population Connectivity in a Complex, Tidally Driven System" (2018). Electronic Theses and Dissertations. 2894. https://digitalcommons.library.umaine.edu/etd/2894 This Open-Access Thesis is brought to you for free and open access by DigitalCommons@UMaine. It has been accepted for inclusion in Electronic Theses and Dissertations by an authorized administrator of DigitalCommons@UMaine. For more information, please contact [email protected]. CIRCULATION, CROSS-SHELF EXCHANGE, AND BLUE MUSSEL (MYTILUS EDULIS) POPULATION CONNECTIVITY IN A COMPLEX, TIDALLY DRIVEN SYSTEM by LeAnn M. Conlon B.S. University of Wisconsin-Eau Claire, 2010 M.S. University of the Virgin Islands, 2013 A DISSERTATION Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy (in Oceanography) The Graduate School The University of Maine August 2018 Advisory Committee: Huijie Xue, Professor of Oceanography, University of Maine, Co-Advisor Philip O. Yund, Downeast Institute Senior Scientist, Co-Advisor Neal R. Pettigrew, Professor of Oceanography, University of Maine David W. Townsend, Professor of Oceanography, University of Maine Ron J. Etter, Professor of Biology, University of Massachusetts- Boston CIRCULATION, CROSS-SHELF EXCHANGE, AND BLUE MUSSEL (MYTILUS EDULIS) POPULATION CONNECTIVITY IN A COMPLEX, TIDALLY DRIVEN SYSTEM by LeAnn M. Conlon Dissertation Co-Advisors: Dr. Huijie Xue and Dr. Philip O. Yund An Abstract of the Dissertation Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy (in Oceanography) August 2018 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. ACKNOWLEDGEMENTS The author thanks committee members Huijie Xue, Phil Yund, Neal Pettigrew, Dave Townsend, and Ron Etter for helpful guidance, discussion, and feedback. Thanks to Steve Cousins for his technical support, Scott Morello for data collection and calculation of reproductive output and spawning time estimates, Kelly Cole for valuable feedback, Changsheng Chen for providing the boundary conditions used for the model, and Mark Bertness for the use of the R/V Buba. This research was funded by NSF grant numbers OCE-13-33797, OCE-14-58239, 1532013 and #11A-1355457 to the University of Maine and OCE-13-33755 and OCE-14-58188 to the Downeast Institute. Project data are available at http://www.bco-dmo.org/project/527082. Computations involved in this study were done using the clusters of the Advanced Computing Group at the University of Maine. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS ............................................................................................ ii LIST OF TABLES ......................................................................................................... ix LIST OF FIGURES ......................................................................................................... x Chapter 1.INTRODUCTION ........................................................................................................ 1 1.1 Introduction ........................................................................................................... 1 1.2 Population Connectivity ......................................................................................... 2 1.3 Gulf of Maine Circulation ...................................................................................... 4 1.3.1 Large-Scale Circulation Patterns ...................................................................... 4 1.3.2 The Gulf of Maine Coastal Current .................................................................. 6 1.4 Cross-Shelf Exchange ............................................................................................ 7 1.5 Bivalve Larvae ....................................................................................................... 8 1.5.1 Background ..................................................................................................... 8 1.5.2 Bivalve Settlement and Recruitment .............................................................. 10 1.6 Approach ............................................................................................................. 11 2.MODEL VALIDATION AND CIRCULATION ........................................................ 11 2.1 Chapter Abstract .................................................................................................. 12 2.2 Introduction ......................................................................................................... 13 2.2.1 Using Numerical Models to Understand Circulation ...................................... 13 iii 2.2.2 Study Location: The Eastern Maine Coast ..................................................... 15 2.3 Methods ............................................................................................................... 18 2.3.1 Numerical Model ........................................................................................... 18 2.3.2 Observations .................................................................................................. 22 2.3.3 Model-Data Comparisons .............................................................................. 22 2.4. Model-Data Comparison ..................................................................................... 24 2.4.1 Temporal Validation ...................................................................................... 24 2.4.1.1 Validation at Buoy I ................................................................................ 24 2.4.1.2 Validation at Tide Gauges ....................................................................... 27 2.4.1.3 Causes for Discrepancies in Temporal Data ............................................. 28 2.4.2 Spatial Data Comparisons .............................................................................. 31 2.4.2.1 CTD Validation ....................................................................................... 31 2.4.2.2 Current Profile Data Validation ............................................................... 34 2.5. Nearshore Circulation ......................................................................................... 37 2.5.1 Tidal Currents ................................................................................................ 37 2.5.2 Residual Flows .............................................................................................. 38 2.5.2.1. Frenchman Bay ...................................................................................... 41 2.5.2.2 Pleasant and Western Bays .....................................................................