| Summary: | Zostera marina L. (eelgrass) is an ecologically important seagrass found in estuaries of the coasts of the North Atlantic, North Pacific, and Europe. This aquatic plant contributes to the high productivity of an estuary ecosystem providing a number of species with habitat, shelter, nursery areas, and food sources. Eelgrass also enhances sediment stability protecting the coast against surface erosion, increases sedimentation and provides nutrients (nitrogen, phosphorus, carbon) to the water column, and improves water clarity. Eelgrass is the dominant seagrass of the temperate waters of the North Atlantic coast with a productivity exceeding most cultivated crops. It successfully inhabits a range of sediments, salinity ranges, and water temperature ranges forming a multidimensional meadow with its linear strap-like leaves and horizontal stems (rhizomes). Zostera is a diploid organism and reproduces vegetatively and sexually. Meadows are primarily maintained via vegetative growth of lateral shoots, but underwater pollination is necessary for seed set and the establishment of new seagrass beds. Zostera's growth is limited by light penetration. The increase in light attenuation found in coastal communities due to human perturbation has reduced the abundance and depth distribution of eelgrass beds. The world-wide decline in eelgrass coverage due to eutrophication has steadily worsened in the last two decades. The potential loss of this valuable aquatic plant from Long Island Sound requires the intervention of conservationists. Knowledge of genetic structure and gene flow is essential in restoring eelgrass beds. This provides managers with the information needed to properly choose individual plants for mitigation in order to maintain and/or enhance diversity. Genetic diversity is an important component of species survival providing individuals with evolutionary flexibility and the ability to respond to changing environmental pressures. Investigations evaluating genetic variability and structure of Zostera marina are few. It is one of the few seagrass species so far investigated that exhibits protein polymorphism. The aim of this study was to investigate isozyme variability patterns in three different populations of eelgrass from Long Island Sound. With the use of starch gel electrophoresis, twenty-one enzyme systems extracted from eelgrass leaves were screened on a tris-citrate, pH 7 gel/buffer system. Of the sixteen enzymes that showed activity, five (acid phosphatase, malate dehydrogenase, peroxidase, phosphoglucoisomerase, and superoxide dismutase) proved to be polymorphic showing variation within and between the three populations examined. Genetic varibility was based on fifteen loci. Percent polymorphic loci ranged from 20.0 % to 33.3 % with the Bushy Point, Groton, population expressing the highest number (5) of variable loci. Reasons for the populations' deviations from Hardy-Weinberg equilibrium were interpreted by x2 and F statistics. Average FST (0.055) suggested a low divergence between the populations. This was further supported by genetic identity coefficients ranging from 99.3 % to 99.9 %. The high genetic similarity between the populations suggests that plants from either site could be utilized for transplantation to other sites in the Sound without the potential loss of genetic diversity. The value of knowing the genetic structure of eelgrass can assist a manager in restoring these ecologically important aquatic plants to an area of great economic importance. "Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Arts in Biology."; Thesis advisor: Clayton A. Penniman.; M.A.,Central Connecticut State University,1996; Includes bibliographical references (leaves 38-44).
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