Award: OCE-1458154

Understanding how populations are connected through dispersal is critical for ecology, evolution, conservation and management, and will play a crucial role in predicting how organisms might respond to contemporary anthropogenic stresses. Many marine organisms disperse in the water column as small larvae. Tracking minute pelagic larvae that drift with the ocean currents and potentially travel tens to hundreds of kilometers during several weeks of development is extremely difficult. We used trace element fingerprints (TEF) derived from the chemical signatures found in calcified structures, such as shells, to quantify dispersal and population connectivity in the blue mussel (Mytilus edulis) throughout the Gulf of Maine over three years (2015-2017). TEFs vary geographically, characterize different water masses, and can be used to identify the location where shell material was deposited. Here we expanded the spatial scale of our previous NSF supported research to encompass most of the Gulf of Maine. Our results indicate that 1) TEFs differ strongly among mussel populations throughout the Gulf of Maine, which has allowed us to assign settlers to natal sites. 2) Inter-annual differences in TEFs, dispersal and connectivity are apparent. 3) Our estimates of larval dispersal and population connectivity indicate that connectivity among populations is typically downstream (NE – SW) of the major coastal currents, although there is some dispersal against the mean flow of the coastal currents. While upstream dispersal may seem odd, it is consistent with what has emerged from preliminary runs of our numerical bio-physical model. 4) We implemented a Bayesian Infinite Mixture Model that takes into account the contribution from potential unsampled mussel populations, allowing us to compare estimates of population connectivity to results from a standard Discriminant Function Analysis. 6) We also developed a hierarchical approach to identify the natal sites of mussels based on TEFs that provides more accurate estimates of dispersal within the Gulf of Maine. Broader Impacts The empirical estimates of dispersal and population connectivity provide important insights into which populations are most important to maintain mussels in the Gulf of Maine and should aid in developing more efficient conservation and management strategies. Four graduate students and ten undergraduate students were trained on a variety of techniques including estimating connectivity, trace elemental fingerprints, population genetics and the physical oceanography in the Gulf of Maine. They were also trained more generally on how to design experiments, test hypotheses and present their findings. Our students included those from various programs at UMB to maximize involvement of underrepresented groups (e.g. REU, Bridges to Baccalaureate Program, Initiative for Maximizing Student Diversity, McNair program). A postdoc was also trained in estimating population connectivity and he developed the software to use a Bayesian infinite mixture model for more accurately assigning mussels to natal sites based on TEFs. Last Modified: 04/30/2020 Submitted by: Ron J Etter