Hauxwell, J. Boston University Marine Program, haux@bio.bu.edu
Cebrian, J. Boston University Marine Program, jcebrian@mbl.edu
Valiela, I. Boston University Marine Program, valiela@bio.bu.edu

 
EFFECT OF MACROALGAL SHADING ON EELGRASS BIOMASS AND GROWTH: UNDERSTANDING EELGRASS DECLINE ASSOCIATED WITH EUTROPHICATION
 
Loss of eelgrass (Zostera marina) habitat often parallels increasing frequency of macroalgal blooms in estuaries worldwide, largely resulting from increased delivery of anthropogenic nitrogen to coastal waters. To evaluate how increased macroalgal biomass affects eelgrass production, we conducted seaweed shading experiments during summer 1998 within eelgrass meadows of two estuaries of Waquoit Bay, MA. While one estuary featured a low nitrogen loading rate, a pristine eelgrass population, and an approximately 2 cm seaweed canopy, the other estuary had a higher nitrogen loading rate, a declining eelgrass population (90% cover loss in past decade), and an approximately 10 cm seaweed canopy. Experimental units were 1 m x 1 m plots of eelgrass fenced within plastic mesh which served to either exclude or include macroalgae at differing canopy heights. In both populations, eelgrass growth rates and densities were lower in seaweed addition treatments than removal treatments. Results of removals were similar to those of controls in the pristine population, but were substantially higher than controls in the declining population. Our results demonstrate that increased macroalgal biomass associated with increased nitrogen loading to estuaries can lead to eelgrass disappearance and identify an approximate 10 cm critical macroalgal canopy height at which eelgrass declines.
 
Day: Monday, Feb. 1
Time: 04:15 - 04:30pm
Location: Sweeney Center
 
Code: SS45MO0415S