Zostera marina (eelgrass) growth and survival along a gradient of nutrients and turbidity in the lower Chesapeake Bay

Survival of transplanted Zostera marina L. (eelgrass), Z. marina growth, and environmental conditions were studied concurrently at a number of sites in a southwestern tributary of the Chesapeake Bay to elucidate the factors limiting macrophyte distribution in this region. Consistent differences in survival of the transplants were observed, with no long-term survival at any of the sites that were formerly vegetated with this species but that currently remain unvegetated. Therefore, the current distribution of Z. marina likely represents the extent of suitable environmental conditions in the region, and the lack of recovery into historically vegetated sites is not solely due to lack of propagules. Poor long-term survival was related to seasonally high levels of water column light attenuation. Fall transplants died by the end of summer following exposure to levels of high spring turbidity (K-d > 3.0) Accumulation of an epiphyte matrix during the late spring (0.36 to 1.14 g g(-1) dry wt) may also have contributed to this stress. Differences in water column nutrient levels among sites during the fall and winter (10 to 15 mu M dissolved inorganic nitrogen and 1 mu M dissolved inorganic phosphates) had no observable effect on epiphyte accumulation or macrophyte growth. Salinity effects were minor and there were no symptoms of disease. Although summertime conditions resulted in depressions in growth, they did not alone limit long-term survival. It is suggested that water quality conditions enhancing adequate seagrass growth during the spring may be key to long-term Z. marina survival and successful recolonization in this region.