productivity. McAlice and coworkers (1978) found that the biomass of 

 phytoplankton was lower in Montsweag Bay than in the Sheepscot Estuary. The 

 lower phytoplankton biomass is attributed to higher turbidity in the shallow 

 bay. 



Tidal fluctuations also may be responsible for changes in phytoplankton 

 composition, particularly in the upper estuary. Phytoplankton samples at the 

 uppermost estuarine station in the Damariscotta River estuary show that 

 species composition of phytoplankton changes with the tides (Petrie 1975). 

 Changes in species composition in Penobscot Bay (Burkholder 1933) and the Bay 

 of Fundy (Gran and Braarud 1935) also have been attributed to tidal 

 fluctuations . 



The only study in Maine which examines phytoplankton communities along the 

 estuarine gradient was conducted by Petrie (1975) in the Damariscotta River 

 estuary. This estuary differs from most in Maine because relatively high 

 salinities were recorded throughout its length, with the exception of the 

 uppermost station. At the other stations, phytoplankton composition was about 

 the same along the estuarine gradient from June to November. In winter, 

 increased spatial heterogeneity is noted. 



A predominance of diatoms rather than dinof lagellates (as in the Gulf of 

 Maine) during the summer in the Damariscotta River estuary probably is due to 

 the availability of ample nutrient supplies (Petrie 1975). Petrie cites 

 Margalef's statement (1963) that the turbulence (in estuaries) overcomes the 

 competitive advantage of being motile and allows the nonmotile diatoms to take 

 advantage of the nutrients. The St. Croix River had a more pronounced diatom 

 abundance than Passamaquoddy Bay (Davidson 1934) . Davidson felt the higher 

 nutrient levels in the estuary partly were responsible. 



In temperate areas, such as the waters of New England, the number of species 

 (diversity) generally increases with a decrease in population size, that is, 

 low chlorophyll concentrations would be associated with high diversity. 

 Seasonal changes in the diversity of phytoplankton populations are apparent. 

 During the slow growth season (summer) no single species is very abundant and 

 diversity is high. Conversely, when growth conditions become favorable 

 (spring) species diversity sharply decreases. This seasonal pattern 

 (corresponding to the nitrogen cycle) has been noted by Petrie (1975) in the 

 Damariscotta River estuary (region 3). The significance of diversity can be 

 seen when growth in rich and poor areas is compared (figure 5-38). In the 

 southwestern regions of coastal Maine the nutrient-rich estuaries generally 

 support phytoplankton populations that are much less diverse than those in the 

 relatively nutrient-poor offshore surface waters. In northeastern Maine 

 (regions 5 and 6) estuaries probably support phytoplankton populations similar 

 to those in the marine system because ocean waters, by which the estuaries in 

 these regions are well flushed, are well mixed and relatively homogenous. 



A succession of zooplankton occurs in estuarine waters of the characterization 

 area. Each species has a seasonal cycle of peaks in abundance followed by 

 decreased numbers. The peaks are not synchronous among species; therefore, 

 the seasonal composition of species is variable. Within each species, 

 propagation is initiated by a few individuals that have survived the winter or 

 by maturation of individuals developing from resting eggs produced the 

 previous year, as may be the case for the copepod Centropages hamatus (Fish 



5-80 



