Apparently, temperature is a very important factor relative to its 

 occurrence in brackish waters, but in the coastal waters, both temperature 

 and its breeding cycle are of equal importance in the seasonal fluctuation 

 of abundance (Bigelow and Sears 1939; and Sherman 1968). 



15.) Coelenterate medusae (hydromedusae and scyphomedusae) 



Medusae are important predators on the smaller zooplankton. Four 

 species of hydromedusae were present in Penobscot Bay: Phialidlum languidum , 

 Sarsia sp. , Bougainvlllia principis , and Stamophora mertensis (Bertrand 1977). 

 The first two species were the only ones which were ever abundant. The 

 most abundant species was P^. languidum which was present from mid June to 

 October. Mayer (1910) reports similar seasonal occurrence for New England 

 coastal waters. Bigelow (1926) notes that in the Gulf of Maine this species 

 is at its peak of abundance. Sarsia sp. was present mainly in the upper bay 

 from May to July. Bertrand (1977) feels that this species comes from local 

 populations. 



Two species of scyphomedusae were present in Penobscot Bay: Cyanea 

 capillata and Aurelia aurita . They are generally common in coastal waters 

 of Maine. In Penobscot Bay, C^. capillata increases in size and numbers in 

 the spring through early summer. Numbers then decline and the adults 

 disappear by October. Reproduction takes place in late August and September 

 and the young jellyfish (ephyrae) grow slowly through the autumn and winter 

 (Bertrand 1977). Similar seasonal patterns were noted by Bigelow (1926) 

 in the inshore waters of the Gulf of Maine. 



In Penobscot Bay, Aurelia aurita occurred in great numbers in late June 

 and July in the third year of a three year study by Bertrand (1977). This 

 would indicate that there are periodic "blooms" of this species. 



16.) Ctenophores 



Ctenophores are important predators on zooplankton, particularly copepods. 

 Three species were present in Penobscot Bay: Bolinopsis infundibulum , 

 Pleurobrachia pileus , and Beroe cucumis (Bertrand 1977) . B^. infundibulum 

 was the most abundant followed by £. pileus and B^. cucumis (Bertrand 1977) . 



Bertrand (1977) found that B^. infundibulum produced three generations 

 a year and had maximal abundances in the winter, spring and early fall. This 

 species is found in such great abundance in Penobscot Bay that the waters 

 are sometimes depleted of the microzooplankton population. In the Gulf of 

 Maine, Bigelow (1926) found that this species only produced one generation 

 per year in late summer to early fall. Many P^. pileus were found in upper 

 Penobscot Bay for the first six months of 1976, which may indicate the 

 reproductive period of this species (Bertrand 1977) . The occurrence of this 

 species in the bay in low numbers in 1974 and 1975 (Bertrand 1977) indicates 

 the patchy nature of populations of this species. Beroe cucumis was found 

 in high abundances in upper Penobscot Bay in early summer 1976 (Bertrand 

 1977). Bertrand (1977) suggests that the population of B^. infundibulum 



(Continued) 



4-F-7 



10-80 



