No abstract

No abstract

No abstract

Within Barnegat Bay, New Jersey, Zostera marina populations have declined by 62% over the last 20 years, and restoration efforts have met with mixed success. We have completed a microsatellite-based genetic investigation of eight populations of Z. marina within Barnegat Bay to determine whether the genetic stock origins of the plants used in management projects may affect restoration success. Additionally, we assessed the genetic diversity of Z. marina in Barnegat Bay to better understand its population structure. Clonal diversity ranged from 0.70 to 0.95 for the populations studied. Individually, Barnegat Bay populations are not genetically diverse, and there is also little divergence among populations. The Atlantic populations had mean Hobs values (0.20-0.34) that were far lower than the Hexp values (0.69-0.83). Also, the F IS values in all of the eastern populations indicate a surfeit of homozygotes over heterozygotes, suggesting a low degree of outcrossing in the Barnegat Bay populations. Six of the ten populations studied (Ham Island, Manahawkin Bay, Shelter Island, Marsh Elder, Harvey Cedar Sedge, and Long Island) show evidence of historical bottlenecks. Mean estimated F ST values would suggest that most alleles are undergoing moderate genetic differentiation, with values that range from 0.06 to 0.13. Oyster Creek and Sedge Island demonstrate the largest estimated effective population sizes and may be the most appropriate populations for use in future eelgrass restoration projects.

The American lobster Homarus americanus and kelp Laminaria longicruris and L. saccharina are prominent and often intimately associated members of the subtidal community in the western North Atlantic Ocean. However, no one has identified the nature of this relationship or specifically investigated whether kelp beds are a superior habitat for lobsters. We conducted field studies in 1990 and 1991 at a coastal site centrally located along the Gulf of Maine. USA, to determine how lobsters use kelp beds as habitat. Identically sized and spaced plots of live and artificial (plastic) kelp were established and monitored for lobster population densities. Adjacent featureless sediment plots of identical size served as controls. Lobster population density and biomass were significantly higher in both real and artificial kelp treatments than in non-kelp control plots (p < 0 0001). The change in lobster density was apparent the day following placement of the expenment, so a secondary trophic effect such as attracting prey into treatments is unlikely to have occurred. Thus, kelp beds can affect local lobster population dens~ties by providing shelter for lobsters, thereby concentrating individuals and increasing the local carrying capacity of potential lobster habitats The effect of kelp beds on the local carrying capacity of lobster habitats was further explored by test~ng how lobsters respond to differing patch sizes. A graded size series of circular patches of artificial kelp was established, in which kelp blade density and total area were held constant for each treatment. Treatments were subdivided into four 1 m', two 2 m*, or one 4 m2 patches. Experiments were surveyed for lobster population density and size structure to determine if statistical differences existed among treatments. Lobster density was significantly greater in the smallest patches (p c 0.001). Moreover, lobsters typically occupied the edges of kelp beds, and their abundance within kelp patches corresponded to the patch's perimeter-to-area relationship. This suggests that 'edge effects' influence the local carrying capacity for lobsters by influencing the lobsters' choice of kelp beds as habitat.

No abstract

No abstract

Zostera marina (eelgrass) can be found in the North Atlantic on the coast of Europe and on the east and west coasts of North America. Over the last 30 years, this once robust species has been reduced to sparse patchy populations due to disease and anthropogenic effects. In order to better understand the consequences of this devastation on the population genetics of the species, we have analyzed the population structure of western Atlantic Z. marina, employing microsatellite DNA polymorphisms. Although high fixation index values suggest moderate genetic differentiation among most of the Z. marina sites, population diversity was low. This lack of diversity was supported by a general dearth of observable heterozygotes in these sites; mean observed heterozygosity values (0.14-0.46) were lower than the mean expected heterozygosity values (0.57-0.81). Additionally, the mean F(IS) (coefficient of local inbreeding) values in these sites were positive, again indicating a surfeit of homozygotes. Allelic richness suggests that Chesapeake Bay has the greatest internal genetic diversity of the sites studied. Inbreeding seems prevalent in these American populations, suggesting possible reproductive fitness problems in the future. There is evidence of demographic bottlenecking and particularly low genetic diversity in Long Island. Northern Maine had the highest effective population size, suggesting a possible use in future restoration projects.