upwelling (see "Hydrography" above) also appear to sustain phytoplankton 

 production through the summer. High amounts of chlorophyll were found in 

 patches at the surface (figure 4-22) before the fall overturn near Monhegan 

 Island (Yentsch and Glover 1977). Also, the continued growth of diatoms 

 through the summer was reported by Hulbert and Corwin (1970) for Casco Bay. 



In temperate ocean waters, such as those of New England, the diversity of 

 species generally increase with decreasing population size; that is, low 

 chlorophyll concentrations are associated with high diversity. Seasonal 

 changes in the diversity of phytoplankton populations are apparent. During 

 the poorest growth season of the year (summer) , no single species is very 

 abundant and diversity is high. Conversely, when growth conditions become 

 favorable (spring), species diversity decreases. This seasonal pattern has 

 been noted by Petrie (1975) in the Damariscotta River estuary (region 3). The 

 significance of diversity can be seen in the comparison of rich and poor areas 

 for growth (figure 4-23). In nutrient-rich estuaries phytoplankton 

 populations are much less diverse than in the relatively nutrient-poor ocean 

 waters . 



A succession of zooplankton species occurs in coastal Maine. Each species has 

 a seasonal cycle of peaks in abundance followed by decreased numbers and the 

 species composition changes with seasons. Within each species, propagation is 

 initiated by a few individuals that have survived the seasonal mortality or by 

 individuals hatched from resting eggs produced the previous year, as may be 

 the case for the copepod Centropages hamatus (Fish and Johnson 1937). The 

 life cycle of zooplankton species is controlled by food supply (quantity and 

 quality) and physical factors (see "Physical/Biogeochemical/ Biological 

 Interactions" above). 



A limited number of zooplankton species are dominant (i.e., abundant) in 

 coastal Maine waters. Reproduction and seasonal abundances vary greatly 

 between species. The life cycles of dominant species (or taxa) in the 

 characterization area (listed in table 4-6) are described in appendix F. In 

 order to determine the potential effect of perturbations on species their 

 seasonal cycles must be known. Much of the data in the appendix are based on 

 two nearshore studies: the first by Bertrand (1977) in Penobscot Bay and the 

 second by Sherman (1966 and 1968) in the coastal waters of Maine. 



According to Sherman (1968), copepods generally accounted for over 70% of the 

 zooplankton in coastal Maine waters (table 4-7), except infrequently when 

 appendicularians (pelagic tunicates) became abundant. In addition to 

 appendicularians , other zooplankton that appear in abundance periodically are 

 comb jellies (Ctenophora) , siphonophores and medusae jellyfish (Cnidaria), and 

 arrow worms (Chaetognatha) . Many of these species are important predators on 

 zooplankton. Therefore, their density has a significant impact on zooplankton 

 populations. Siphonophores have an impact on the fishing industry (see 

 appendix F) . Euphausiids (krill, shrimplike animals) are a small but 

 relatively consistent proportion of the zooplankton in spring and summer 

 (Sherman 1968). 



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