CAREER: Connectivity Among Marine Fish Populations: Emphasizing Ecological Links Between Estuaries and the Coastal Ocean through an Integrated Program of Interdisciplinary Res/Educ

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The need for spatially?explicit models of marine populations has become obvious as fisheries scientists search for alternatives to traditional management strategies for marine resources. Efforts to develop spatial models for marine fish populations have been handicapped, however, by the absence of quantitative estimates of exchange rates among geographically?separated groups ("connectivity"). This lack of knowledge is primarily due to the difficulty of conducting mark?recapture studies in species that are characterized by the production of large numbers of small pelagic offspring that suffer high initial mortality rates. In this study, Dr. Thorrold will continue development and application of a marking approach that relies upon natural variations in the geochemistry of fish otoliths (ear bones) as a marker of source location. Recent work suggests that it is possible to track individual fish from juvenile nursery areas to adult spawning locations using these geochemical signatures as a natural tag of natal location. The otolith is an ideal natural tag because:Deposition time of any material in the otolith can be determined by reference to periodic increments in the otolith.Otoliths are metabolically inert, and material is not re?worked or re?sorbed after deposition.The chemical composition of the otolith reflects, to some degree, the environment in which the fish has lived. They will begin with a series of laboratory studies to investigate factors influencing the elementalcomposition of otoliths in larval Atlantic silversides (Menidia menidia). Then characterizegeochernical signatures in otoliths of young?of?the?year (YOY) Menidia from 10 estuaries along the coastof New England. Otoliths will be assayed for VC, 8"0, "Sr/16 Sr ratios, and a number of trace elements(Mg/Ca, Mn/Ca, Sr/Ca and Ba/Ca). This process will include the development of a technique forquantifying 87 Sr/ 86 Sr isotope ratios in otoliths using multi?collector inductively coupled plasma massspectrometry. The resulting multivariate chemical signatures in these otoliths will be used to developmaximum likelihood estimators to classify adult Menidia returning to estuarine waters to spawn thefollowing year. Otoliths ftom spawning adults will be sectioned to reveal the section of the otolith laiddown during juvenile residency in their natal estuary. A combination of micro?drilling and laser ablationICP?MS will be used to assay geochemical signatures in this portion of the otolith. Adult fish collectedfrom each of the 10 estuaries will be assigned to natal estuary based on the MLE algorithm developedfrom ground?truthed signatures of juveniles captured in the estuaries the previous year. These data willprovide quantitative estimates of connectivity through natal homing and straying in a coastal fish specieson an unprecedented spatial scale. More generally, the study will provide a framework for research aimedat quantifying connectivity in marine ecosystems through the use of natural signatures in calcifiedstructures of marine organisms. The educational component of the proposed research will include thedevelopment of topics courses in fisheries ecology and oceanography for the MIT[WHOl joint program inbiological oceanography, the mentoring of undergraduates on summer student fellowships at WHOI, andthe development and implementation of teacher training workshops for high school teachers inMassachusetts. They will focus on a common fish species that is a critical component of coastal habitatswith which students are most familiar. The ability to track the movements of fish from the backdoors oflocal students to other estuarine and coastal habitats will stress the interconnectedness of salt marshes,estuaries and the coastal ocean.