ECOLOGY OF BUZZARDS BAY: An Estuanne Profile 



25 



The subtidal basin topography has undergone 

 alterations as well, mainly smoothing (Fig. 2.4) re- 

 sulting from erosion of shoals and increased depo- 

 sition in hollows. However, like the beaches, the 

 shoals (formed from the same materials) also form 

 a coarse surface layer slowing their erosion. The 

 major alteration has been the deposition of fine- 

 grained sediments in the central bay, producing a 

 gently sloping bottom (Hough 1940). 



Overall, Buzzards Bay is identified as a net depo- 

 sitional area (Camp, Dresser, and McKee, Inc. 

 1 990). with a progression of silts and clays being 

 transported from the outer continental shelf into the 

 bay and subsequently into the smaller associated 

 embayments like New Bedford Harbor. Sediments 

 within the bay range from muds and silts in the 

 deeper regions to sands, gravels, and boulders in 

 shallower areas nearshore and near the eastern head 

 of the bay (Fig. 2.5). Almost all of the deposited 

 sediments have terrestrial origins rather than ma- 

 rine, indicative of deposition from runoff or glacial 

 activity. 



Silt is found in the deeper, central regions of the 

 bay generally below the 12.2-m contour (Figs. 2.4 

 and 2.5), with fine sand along the nearshore depo- 

 sitional areas of the north shore but medium sand 

 close to shore on the south side. Coarse sand is 

 also associated with the sandy protuberances ex- 

 tending out off Penikese, Pasque, and shoal areas. 



as well as in the vicinity of rocky submarine expo- 

 sures around New Bedford Harbor, Nasketucket 

 Bay, and the northeast shoal areas of the upper bay. 

 Areas of coarser sand are swept by stronger cur- 

 rents that remove finer sediments (Moore 1 963 ). 

 These physical features produced by glacial 

 transport and sorting of benthic sediment by tidal 

 and wind-driven currents have created a textural 

 and depositional environment that exerts a signifi- 

 cant effect on the distribution and composition of 

 today's benthic plant and animal assemblages. The 

 communities inhabiting rocky versus sand/silt and 

 clay bottoms are very different because organisms 

 attach to a rock substrate and burrow into a fine- 

 grained one. Most of Buzzards Bay consists of fine 

 sand to silt-sized sediments, and in these areas, sedi- 

 ment characteristics, including grain size and sedi- 

 ment composition, are major determinants of the 

 structure of bottom-dwelling communities. Larval 

 stages of many benthic animals, particularly inver- 

 tebrates and bivalves, require certain sediment con- 

 ditions for successful settlement. Grain size is a lim- 

 iting factor for young larvae that burrow into the 

 bottom and become established. The result is that 

 given the relative stability of the sedimentary envi- 

 ronment of Buzzards Bay (Moore 1 963), the geo- 

 logic history of the region has played a central role 

 in the distribution of today's animal and plant 

 communities. 



