PLANKTON OF THE GULF OF MAINE 31 



To answer a question that has often been asked me by zoologists as well as 

 laymen, I may remark that there is no level in the Gulf of Maine but supports a 

 varied pelagic fauna. 



NERITIC AND OCEANIC PLANKTON 



None of the criteria by which the plankton can be subdivided ecologically (e. g., 

 relation to temperature, season of reproduction, depth of habitat, etc.) is more 

 fundamental than whether its members do or do not depend on the coast line with its 

 shallows and great supply of foodstuffs; that is, whether they are neritic or oceanic. 

 This distinction is as interesting to the oceanographer as to the biologist, a know- 

 ledge of the mutual distribution of the two groups on the high seas often going far to 

 reveal the mutual relationships and fluctuations of waters of coastal and of offshore 

 origin. 



The pelagic larva? of various familiar bottom-dwelling animals (a host in them- 

 selves), including most of the worms, bivalve and gastropod mollusks, decapod 

 crustaceans, barnacles, starfishes, and sea-urchins, so abundant in the bays and 

 shallow waters along the coasts of the Gulf of Maine, belong to the neritic category. 

 The adults of many medusas, including the largest and most conspicuous species as 

 well as others minute, are equally neritic, for they pass through a fixed stage in shallow 

 waters during early life. Here, also, fall certain small phyllopod crustaceans (e. g., 

 Evadne), which, though pelagic for most of their lives, survive unfavorable seasons 

 in the form of resting spores on the bottom, a life history analogous to that of many 

 diatoms, which consequently fall in the neritic category also, as do various other pelagic 

 plants less prominent in the plankton. There is also a whole series of planktonic 

 animals, particularly among the copepods, bound to the neighborhood of the coast 

 by some unknown bond (perhaps by dependence on a particular food supply), and 

 hence to be classed as neritic, although they are pelagic throughout life both as 

 larvas and as adults. Here, too, must be classed the pelagic eggs of all the species of 

 fish that spawn in shallow water, such as cod, haddock, pollock, silver hake, cunners, 

 and flounders of sundry species. 



Contrasted with this coastwise population of the open sea are all the oceanic 

 animals and plants, which are not only free floating or swimming throughout life but 

 show no apparent relation to the coast line in their distribution — to borrow a nautical 

 term, they form its "blue water" population. 



It is, of course, impossible to draw a hard and fast distinction between the neritic 

 and oceanic categories, the border line being bridged in too many instances by the 

 many pelagic forms occurring indifferently both near shore and out at sea, and also 

 by animals that are dependent on the bottom in deep water at some stage of existence 

 but not in shallow water; for example, by the hydromedusan genus Calycopsis, 

 wluch probably passes through a fixed stage but has never been found nearer shore 

 than the continental slope. However, the division holds fairly well for the Gulf 

 of Maine. 



In northern seas, generally, neritic elements form a large part, if not practically 

 the whole, of the plankton of sheltered bays and estuaries and off river mouths — 

 75898—26 3 



