PLANKTON OF THE GULF OF MAINE 15 



THE PLANKTON 



Although of rather recent birth as words go, 3 the term "plankton" filled so 

 obvious a need that it is now in general use to cover a whole assemblage of organ- 

 isms, plant and animal, related by their manner of life though they may be far 

 apart in the systematic scale. By it we understand all such forms as float or swim 

 freely in the water, but which, however active, are unable to carry out voluntary 

 horizontal journeys of any extent, though certain of them perform considerable ver- 

 tical migrations under the directive influence of sunlight or of some other physical 

 stimulus. Among the three major faunistic groups into which the inhabitants of 

 the sea may be divided — bottom dwellers, free swimmers, and plankton — the im- 

 portance of the last in the economy of nature was slowest in gaining general appre- 

 ciation. Within the last half century, however, biologists have come to realize 

 both that the number of species of this category is past all counting and that the 

 microscopic pelagic plants are the chief producers — that is, are capable of elaborating 

 simple inorganic compounds into complex organic matter — in the sea. They serve 

 as food supply for many larger marine animals at one stage or another, and thus 

 play a most essential role in the general nutritive scheme of marine life. As it 

 chances, the planktonic plants (producers) as a whole are unicellular and microscopic; 

 the planktonic animals (consumers) are multicellular and comparatively large, so 

 that the oft-employed terms " microplankton " and " macroplankton" are not em- 

 piric, but do classify the plankton roughly as vegetable or animal, more technically 

 as phytoplankton or zooplankton. 



In the following pages I have attempted to place before the reader a general 

 survey of these two great planktonic divisions as they occur in the Gulf of Maine, 

 followed by more particular accounts of the status of such groups of each as loom 

 large in its pelagic communities at one time or another. Many other groups are 

 also represented in the tow nettings, but time and the assistance available have so 

 far allowed examination of those only that are dominant or numerically important 

 in the Gulf at one time or place or another. 



Study of the occurrence of buoyant fish eggs is not sufficiently advanced to 

 warrant more than a few preliminary notes here. The present knowledge of the 

 breeding grounds and seasons and of the distribution of the eggs and larva? of Gulf 

 of Maine fishes is summarized by species in the first part of this report (Bigelow 

 and Welsh, 1925). 



> The term was coined in 1886 by Hensen. 

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