Stellwagen Bank Final EIS and Management Plan 



Page 19 



b. Zooplankton 



the autiimn months in the Gulfs coastal waters. 



The vast majority of zooplankton species are 

 endemic in origin, and reproduce with sufficient 

 frequency to maintain a local stock within the 

 boundaries of the Gulf of Maine. The coastal zone 

 (shallower than 100 m) is generally more productive 

 for zooplankton (particularly for Calanus) than the 

 central basin area. Deeper waters of the Gulf are 

 important reproduction areas for Pseudocalanus and 

 Oithona . 



The total amount of zooplankton biomass is 

 usually greater in deeper waters (greater than 100 

 m); though more concentrated in shallower waters. 

 Massachusetts Bay is highly productive for copepods 

 and pelagic fish eggs. Smaller copepods are found 

 in greater concentrations in shallow waters; larger 

 species in deeper waters. Zooplankton densities are 

 greater in stratified western coastal areas than along 

 the turbulent eastern coast of the Gulf. 



Although the Gulf of Maine is rich in 

 zooplankton species (more than 160 identified), 

 faima are dominated (over 80%) by only three or 

 four species. Fauna are dominated by crustaceans, 

 primarily copepods (and most prominently. Calanus 

 finmarchicus). An exception to this dominance 

 occurs nearshore in the spring when barnacle 

 nauplii, or occasionally euphausids, ctenophores and 

 other zooplankters, may swarm locally (Fish and 

 Johnson, 1937). 



Other less numerous species of the Calanus 

 community include the copepods, Pseudocalanus 

 minutus and Metridia lucens . Other, less abundant 

 species include the chaetognath. Sagitta elegans : the 

 amphipod genus Euthemisto; and euphausid genera 

 Thvsanoessa and Meganvctiphanes : and the 

 cetenophore, Pleurobrachia pileus (Cohen, 1975). 

 The abundance of all zooplankton forms is greater 

 in the western coastal sector than in the eastern 

 coastal sector. 



The two Calanus species, £, finmarchicus and 

 Pseudocalanus minutus account for more than 70% 

 of the zooplankton biomass in winter, spring and 

 summer. Three species - Pseudocalanus minutus . 

 Temora longicornis . and Centropages tvpicus — 

 compose 85% of the zooplankton biomass during 



During summer months, three major groups of 

 zooplankton can be identified based on their 

 seasonal vertical distribution. The surface layer 

 contains small, young forms of copepod nauplii, 

 copepodites, fish eggs, fish larvae and smsdl 

 copepods. The second layer contains the boreal 

 Calanus community, which occurs generally in mid- 

 depths above 100-150 meters, but below the surface. 

 The third zooplankter group occurs in deeper 

 waters of the Gulf, and is characterized by the giant 

 copepod, Euchaeta norvegica . Also included, in 

 lesser amounts, are the chaetognaths Eukrohnia and 

 Sagitta lyra : the decapod shrimp, Pasiphaea and 

 Meganyctiphanes norvegica . 



Differences among these three communities are 

 most pronounced in the summer when waters over 

 the deep basins and in the western Gulf are 

 markedly stratified. Differences are least apparent 

 in well-mixed waters, i.e., shallow areas of heavy 

 tidal mbdng, and throughout the Gulf during winter 

 and spring. In general, copepod densities are 

 greatest at deeper levels in the nearshore areas of 

 the Gulf (Sherman, 1976). 



Gulf of Maine zooplankton generally may be 

 divided into two fundamental ecological subsets - 

 neritic and oceanic — depending upon their degree 

 of dependence on shallow, food-rich coastal zone 

 waters. Water depth, in fact, is the single most 

 important parameter influencing the distribution of 

 zooplankton in the Gulf of Maine (Sherman, 1976). 

 Typical neritic zooplankton are larval stages of 

 various benthic organisms, such as barnacles, 

 worms, bivalve and gastropod mollusks, decapod 

 crustaceans, and echinoderms. Also included in this 

 group are pelagic eggs and larvae of all fish species 

 that spawn in shallow waters. Oceanic zooplankton 

 are pelagic throughout their life, and show no 

 particular dependence on coastal areas. Neritic 

 organisms are rarely encountered outside the 100- 

 meter (328 ft.) isobath. 



Zooplankton do not pass through the seasonal 

 pattern of succession as phytoplankton species; 

 rather, zooplankton stay quaUtatively the same 

 throughout the year, while experiencing quantitative 

 changes in total biomass. Zooplankton begin spring 



