BIGELOW: EXPLORATIONS OF THE COAST WATERS. 251 



part of the Gulf (the immigrants from northern and from tropical 

 waters discussed above, p. 246, 247) and the local swarming of animals, 

 such as Pleurobrachia, which occur in small numbers elsewhere in the 

 Gulf. 



Oceanic and neritic Plankton in the Gulf of Maine. — The influence of 

 the coast line on the plankton is now generally recognized; and the 

 distinction between oceanic and neritic forms has often been drawn; 

 the latter term embracing such organisms as are actually dependent 

 upon the bottom in shallow water, in order to pass through some stages 

 in de\elopment (Gran, 1915). This, of course, includes forms which 

 pass the winter, or other unfavorable seasons, on the bottom as resting 

 spores {e. g., some diatoms); the eggs and larvae of bottom-dwelling 

 Metazoa, and Metazoa which pass through a fixed stage in develop- 

 ment, as so many hydroid medusae do. Considering the length and 

 complexity of the shore-line of tlie Gulf; its rich littoral fauna, and 

 the very considerable amount of land water which the rivers pour into 

 it, we might naturally expect its endemic plankton to be largely re- 

 cruited from the shallow coastal zone; and it is a commonplace, for 

 the Gulf as truly as for the eastern side of the Atlantic, that various 

 neritic organisms often swarm near shore, particularly in the estuaries, 

 bays, and sounds and among the numerous rocky islands. 



But in our four years experience we have never found them playing 

 a role of any importance in the plankton of the central parts of the 

 Gulf; and how rare they are, except, within a trivial distance of the 

 land, may be illustrated by the following facts of distribution. We 

 have always found neritic diatoms, of which Thalassiosira gravida, 

 Th. nordenskioldi, Chaetoceras debile, Asterionella japponica, and Guin- 

 ardia, may serve as examples, (Ostenfeld, 1913; Gran, 1902), practi- 

 callv limited to a narrow coastal zone hardlv over fifteen miles broad, 

 including the sounds and bays among the islands; and to the shallow 

 waters over Georges Bank (p. 321). 



A similar state of affairs obtains for the neritic Metazoa. For 

 instance, one of the most striking features of our hauls has been the 

 rarity of the neritic Scyphomedusae, Aurelia and Cyanea, in the center 

 of the Gulf, contrasted with their abundance along shore (1914a, p. 

 124, pi. 6. Aurelia, in fact, is seldom seen more than a few miles 

 from land; and though Cyanea is not so closely restricted, it is abun- 

 dant only along the coastal zone, and in the shallow waters of Nan- 

 tucket Shoals and Georges Bank. 



Perhaps the most important index to land water among the Hydro- 

 medusae, because of its size, abundance, and the fact that its fixed 



