PLANKTON OP THE GULF OF MAINE 
91 
On the whole, it is in late winter and early spring, when the physical characters 
of the sea water are most uniform vertically and when its vertical stability is least, 
that the zooplankton of the Gulf of Maine and of other boreal seas most nearly 
approaches vertical uniformity of distribution. At this season, as illustrated by the 
March cruise of 1920, the volumes of zooplankton present in the water are so small 
in all parts of the gulf, and the depth of water through which it was distributed at 
the more productive localities is so considerable, that the volume per cubic meter 
(by direct calculation) was only 0.7 to 1 cubic centimeter even where the plankton 
was densest — for instance, in the eastern and northeastern troughs of the basin, in the 
Eastern Channel, and over the northeastern and southeastern parts of Georges Bank. 
It ranged down from this to a minimum of practically nothing in the deep water in 
the southeastern corner of the gulf, the average for all stations being about 0.4 cubic 
centimeters, which is something less than half the summer average by the lowest 
possible estimate. Nor is it likely that this calculation seriously understates the 
density of aggregation of the zooplankton for any large portion of the gulf in March, 
because there was little evidence of vertical stratification during that month. 
Zooplankton volumes per cubic meter, March, 1920 
Locality 
Date 
Station 
Cubic 
centi- 
meters 
per cubic 
meter 
Locality 
Date 
Station 
Cubic 
centi- 
meters 
per cubic 
meters 
Western Basin.. 
Feb. 23 
Mar. 1 
20049 
20050 
0.6 
. 1 
Georges Bank: 
Northeast part 
Mar. 11 
20065 
.0 
Mar. 2 
20052 
. 1 
Eastern part 
...do. 
20066 
.3 
Mar. 3 
20053 
.3 
Southeast part 
Mar. 12 
20067 
.5 
...do 
20054 
.4 
Southeast slope 
...do 
20068 
1.7 
...do 
20055 
.5 
Northeast part 
Mar. 13 
20070 
.0 
...do 
2005G 
.2 
Eastern Channel 
20071 
.7 
Mar. 4 
20057 
.2 
Fundy Deep _ 
Mar. 22 
20079 
. 1 
OS Seguin Island 
...do. 
20058 
.5 
Off Machias (Me.).. 
Northeast trough 
Off Yarmouth, Nova Scotia 
___do._ . 
20080 
.4 
...do.. _ 
20060 
.2 
...do. _. 
20081 
.7 
20061 
. 1 
Mar. 23 
20083 
.4 
...do. .. 
20062 
.5 
Off German Bank 
do.. . 
20086 
.5 
North of Georges Bank 
Mar. 11 
20063 
. i 
Western Basin 
Mar. 24 
20087 
.4 
Southeast Deep 
...do 
20064 
.0 
Off Boston 
Apr. 0 
20089 
.4 
With the advance of the spring the concentration of the plankton is augmented 
both by the increase in the total amount present in the gulf, just remarked, and by 
its stratification at one level or another. Not only does the first of these factors 
raise the volume per cubic meter to 2 to 4 cubic centimeters at the very least by 
midsummer in such prolific though rather shallow regions as the waters off Cape 
Cod, the neighborhood of Cape Sable, and the eastern part of Georges Bank, 43 but 
stratification may result in a far denser concentration of the plankton at some 
particular level while rendering other strata of water far more barren than the 
ostensible volumes per cubic meter (as derived from the usual calculation) would 
call for. We have encountered this phenomenon in its most extreme form in the 
deeper parts of the gulf, but experience has shown that a greater or less tendency on 
the part of the zooplankton, as a whole, to congregate at some particular level is to 
be expected anywhere in the gulf in summer, leaving the shoaler as well as the deeper 
<3 Plankton volumes per cubic meter, calculated from our summer and autumn hauls, have been published already; those for 
the year 1913 in Bigelow, 1915, p. 326; for 1914 and 1915 in Bigelow, 1917, pp. 310 and 314; and for 1916 in Bigelow, 1922, p. 136. 
