Beal, B.F., Vadas, R.L., Sr., Wright, W.A., Nickl, S.
We estimated the aboveground productivity of eelgrass, Zostera marina, in Cobscook Bay at three soft-bottom lower intertidal locations during 1995–1996. Approximately 30 plants were tagged bi-weekly or monthly at two sites where we used a completely randomized block design to assess spatial variability in leaf initiation and elongation rates. The data showed strong seasonal patterns with highest rates from June–September and lowest rates from November–April. At one site, Bell Farm, plants were tagged at two discrete tidal levels (intertidal and sublittoral fringe). On each sampling date, mean leaf biomass and new leaf production were 2.7 and 1.7 times greater, respectively, for plants in the sublittoral fringe. At another site, Mahar Cove, all tagged plants were restricted to one tidal level. Spatial variation in leaf biomass and new leaf production were examined on the first four sampling dates and significant effects were observed twice. Productivity estimates ranged from 0.095 g dry wt m-2 day-1 (November–January) to 1.215 g dry wt m-2 day-1 (August) at Bell Farm. At Mahar Cove, rates ranged from 0.176 g dry wt m-2 day-1 (March–April) to 1.490 g dry wt m-2 day-1 (August). Average annual productivity at Bell Farm and Mahar Cove was 0.481 ± 0.512 g dry wt m-2 day-1 and 0.784 ± 0.512 g dry wt m-2 day-1, respectively. These estimates correlate directly with seawater temperature, but not with salinity, nitrate, and total phosphorous. The time for plants to fully turn over their leaves at the two sites ranged from 50.5–56.7 days (6.4–7.2 turnovers per year), and are comparable to other locations in the northeast US and the Canadian Maritimes. We estimate that total (interidal + subtidal) eelgrass production in Cobscook Bay ranges from 3.3–5.3 x 108 g C year-1. This is the first appraisal of growth and productivity of Z. marina in eastern Maine.