SUN AND HARVEST OF THE SEA—SCHMITT 303 
roughly 2,500,000 individuals, chiefly Calanus finmarchicus, the 
dominant copepod in the Gulf of Maine. The abundance of this 
species makes it the most important North Atlantic consumer of 
marine plants on the one hand and the most valuable food for the larger 
carnivorous marine animals, both invertebrate and vertebrate, on the 
other. According to Farran, in the path of the Labrador current along 
the coast of North America Calanus finmarchicus forms in the summer 
months a rich belt which is at least 500 miles wide off Newfoundland. 
An evaluation of what copepods mean in terms of diatoms and peri- 
dinians has been made by Johnstone. He found that while it took 
from 300,000 to 500,000 copepods to make 1 gram of dry copepod sub- 
stance,® an equivalent mass of dry phytoplankton material required 
675 millions of specimens of the diatom Chaetoceras or 42 to 65 mil- 
lions of peridinians. On this basis 1 copepod contains about as much 
substance as 135 peridinians or 1,687 diatoms. The dry substance of 
1 peridinian equals that of 12 diatoms. 
Coming back now to the Gulf of Maine, where Redfield restudied 
the distribution of the calanoid community in 1933 and 1934, we learn 
that the average haul for all sectors of the Gulf and for all cruises 
consisted of about 40 cubic centimeters of “dry”? plankton. This, if 
the area of the Gulf be taken at 36,000 square miles, according to 
Redfield’s figures, would indicate a total population of primarily 
crustacean grazers aggregating some 4 million tons. Copepods pre- 
dominated among the crustacean grazers making up this immense mass 
of animal matter nurtured in that body of water. Yet the euphausid 
shrimps must have formed no inconsiderable part of that mass. 
Though figures as detailed as those available for the copepod grazers 
are not at hand for the euphausids, it is known that in various places 
they occur in almost equally great numbers. Bigelow speaks of sev- 
eral half-hour surface and vertical hauls from 60 to 100 meters which 
returned 500 cubic centimeters of zooplankton, “chiefly euphausids.” 
S. I. Smith and Verrill have told of the swarms of euphausids in the 
Eastport region “filling the water for miles,” and of the occasion when 
they were so abundant among the wharves at Eastport that they could 
be dipped up by the quart. From a study of the food habits of certain 
fishes and whales, euphausids are seen to be as important as copepods 
in converting the ocean’s pasturage into food for higher animals, car- 
nivorous and omnivorous. 
Most animals feeding directly on plant or animal plankton are 
equipped with filters, or strainers, which enable them to strain these 
small organisms from the water. The filtering apparatus in crusta- 
ceans, which include the euphausids and copepods, is made up of 
6 Dry weight in this instance is based upon a completely desiccated sample. 
™The plankton, after removal from the tow net, was collected on filter paper and 
suction applied to the funnel until the fluid in which the catch was preserved ceased to 
flow. 
