Eelgrass (Zostera marina L.) shoot density, seed-bearing shoot abundance, shoot length, and standing stock biomass were monitored during summer months from 1985 to 2000 at three locations in eastern Long Island Sound (LIS) near Millstone Power Station (MPS), Waterford, Connecticut, USA. Short-term declines in eelgrass abundance were directly associated with fouling and overgrowth of eelgrass on two occasions; once by blue mussels (Mytilus edulis) and once by a bloom of green algae (Cladophora spp.). Analysis of long-term trends indicated some degree of decline in most of the parameters examined at all three areas monitored. The spatial relationship of the long-term eelgrass declines suggests primary causal factors other than the power plant discharge or regional climate change. Two populations to the east of MPS and near the fringes of the thermal plume ( < 1.5 km from the MPS discharge to LIS) exhibited only slight declines over the 16-y study period and thermal input from MPS to these sites was minimal ( < 1 °C above ambient conditions). By comparison, heavy eelgrass losses were documented in the Niantic River, located >2 km from the power plant thermal plume. Die-offs of entire individual eelgrass study beds in the Niantic River were observed on five separate occasions during the study with no sign of recovery. While the causes were not determined, anthropogenic influences such as nutrient loading from surface run-off and groundwater sources may have contributed to observed declines. The Niantic River has a more restricted tidal inlet and is closer to sources of nutrient enrichment than Jordan Cove. Historically, eelgrass has ranged to far western reaches of LIS, but over the last century has become restricted to the easternmost third of the Connecticut coastline due to nutrient loading and eutrophication of the western portions. This study suggests that the west-to-east declining trend in eelgrass distribution in LIS may be further progressing.
Eelgrass (Zostera marina L.) is the dominant marine angiosperm in temperate coastal regions of the northern hemisphere (Setchell, 1935; Thayer et al., 1984). Extensive eelgrass meadows found in shallow estuaries and lagoons provide multi-level ecological benefits that make them key components to many coastal marine systems. High eelgrass primary productivity is utilised directly by many consumers including numerous waterfowl, fish and invertebrate grazers (see review by Valentine and Heck, 1999), but much of the production enters the foodweb through the detrital pathway (Thayer et al., 1984). Increased habitat complexity within eelgrass meadows enhances primary and secondary production and species diver- sity in coastal ecosystems (Hughes et al., 2002). Eelgrass meadows support productive epiphytic communities (Thayer et al., 1984; Nelson and Waaland, 1997) and provide feeding and nursery grounds for many species, including commercially important fin- fish and invertebrates (Orth, 1973; Heck et al., 1989, 1995; Mattila et al., 1999; Short et al., 2001).