29 



Relative contribution of eelgrass production in Buzzards Bay and 

 adjoining shallow embayments 



Most of Buzzards Bay is too deep to support eelgrass growth, hence 

 eelgrass and epiphytic algae contribute only 13% of the total production 

 in Buzzards Bay (Table 1). In contrast, eelgrass communities may 

 account for a larger portion of total production in shallow embayments. 



For example, Buttermilk Bay is a 210 ha lagoon at the north end of 

 Buzzards Bay with a mean depth of 1.0 m (Costa, 1988; Valiela and Costa, 

 in press) , and 47 ha of eelgrass production area (Appendix III) . 

 Assuming eelgrass production rates described above, then Zostera 

 production in Buttermilk Bay equals 1.6 x 10° g C y"-'-. 



Other producers can also be estimated as before. Algal epiphytes 

 are very abundant in parts of Buttermilk Bay, and if the equal 40% of 

 Zostera production (Penhale, 1977) , they account for an additional 0.7 x 



Q _1 



10° g C y ■^. In a shallow, enriched Rhode Island lagoon, Nowicki and 

 Nixon (1985) estimated phytoplankton production to 120 g C m~^ y"-*-. If 

 Buttermilk Bay has similar rates of production, then phytoplankton 

 produce 2.5 x 10^ g C y~^. 



Drift algae are abundant in some areas of Buttermilk Bay, (Costa, 

 1988). Algal biomass in 1985 was 77 g dry wt m~^ (n=8, se=22) in a 

 transect from mid-bay to Red Brook. If annual production is 6x summer 

 biomass then annual production is -500 g C m~^ y~^. This transect was 

 centered near a major source of nutrients, and probably overestimates 

 algal abundance in the Bay. In Buttermilk Bay, drift algae occur mostly 

 in quiescent areas, depressions, or tangled within eelgrass shoots, 

 especially near nutrient sources. Total drift algae area was 



