PLANKTON OP 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. Am ong 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 larvae 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. 
