ECOLOGY OF BUZZARDS BAY: An Estuarine Profile 



57 



beds in areas where light penetration is sufficient to 

 support growth. Eelgrass is a perennial angiosperni 

 (Fig. 4.5) that is able to flower and undergo polli- 

 nation, seed dispersal, and growth completely un- 

 derwater. Propagation of this species is primarily 

 by rhizome within existing beds and by seedlings in 

 new growth areas. 



Eelgrass beds are important to the bay ecosys- 

 tem as sources of organic matter production (Table 

 4.5). as habitat for invertebrate and fish species 

 (Adams 1 976; Thayer et al. 1 984), and as a food 

 source for geese (Buchsbaum and Valiela 1 987). 

 Eelgrass beds alter hydrodynamics and generate 

 low-velocity zones, causing sediment and organic 

 matter deposition that secondarily affect benthic ani- 

 mal communities. The roots and rhizomes serve both 

 for nutrient uptake and binding the substrate. The 

 plants themselves become a substrate for attach- 

 ment of epiphytic organisms and the eggs and 

 larvae of various species. 



Algal 

 epiphyte 



Unfertilized 

 er 



Inflorescence with 

 mature seeds 



Root cluster 

 on rhizome 

 node 



Fig. 4.5. The general morphology of the eelgrass 

 Zostera marina. From Costa (1988a) 



Buzzards Bay populations of Zostera appear 

 to have generally recovered (Costa 1988b) from 

 the catastrophic decline because of a lasting" dis- 

 ease (Tabarynthula), which decimated eelgrass beds 

 throughout New England from 1931 to 1933 

 (Cottam 1 933). Costa ( 1 988b), using aerial pho- 

 tographs, determined that several years after the 

 decline, eelgrass beds in Buzzards Bay covered less 

 than 1 0% of the present area. Although epidemics 

 of "wasting" disease have not reoccurred since the 

 1 930's in Buzzards Bay, smaller outbreaks have 

 been found in New England (Short et al. 1 986). 



Zostera appears to colonize sandy and mud 

 bottoms of the open bay and its embayments. The 

 major factor determining the upper limits of this 

 subtidal species appears related to desiccation in 

 summer and ice scour in winter (Davis 1913; Costa 

 1 988b). While the lower limit is set by light pen- 

 etration (Dennison and Alberte 1985, 1986), the 

 level of light intensity is less important in determin- 

 ing depth than the daily duration of intensity above 

 a physiologically set level. 



Light penetration in simplest terms is a function 

 of depth and the concentration of particles within 

 the water column. The particles can be living (phy- 

 toplankton) or inert (sediments). Because Buzzards 

 Bay has no large river discharging into it and rela- 

 tively coarse-grained sediments resulting from its 

 formation, the major source of particles attenuating 

 light is generally phytoplankton within the water 

 column (and epiphytes on the eelgrass leaves). As 

 a result, light attenuation relative to eelgrass growth 

 in Buzzards Bay may be more directly related to 

 factors controlling phytoplankton and epiphyte den- 

 sity (e.g., nutrients) than in other systems with a 

 higher inorganic load. Shallow protected 

 embayments support less than one-third of the eel- 

 grass of Buzzards Bay. The nearshore zone of the 

 open bay. with its greater circulation and water trans- 

 parency, contains beds as deep as 6 m, although 3- 

 m beds are much more common. Compared to the 

 open water areas, eelgrass growth in the more tur- 

 bid embayments is restricted, generally growing in 

 depths of 0.6 to 1 .8 m (Costa 1 988b). 



Examination of the maximum depth of Zostera 

 growth at sites throughout the bay (Fig. 4.6) 



