PLANKTON OF THE WOODS HOLE REGION 101 
spring. The warmest months were July and August; the coldest were January, 
February, and March. 
The strong currents rushing through the “Hole” on the flood tide churn the 
water to such an extent that any change in the temperature of the air affects the 
bottom water as quickly as it does that of the surface. Table 2 gives a series of 
temperature observations taken when the temperature was suddenly rising or fall- 
ing. These show the result of the mixing of the waters. 
TaBLe 2.—Surface and bottom temperatures taken at Woods Hole in 1922-28 
°C. at °C. at °C.at | °C. at 
Date surface | bottom Date surface | bottom 
Fi Ge ee 20.2 20} Allee 19200 woes ieee Tne ole 3 3 
RU yrds 9 20 ee eee 21,2 PB OY hoa Diets tala Kt ae ee 1 1 
July 31, 1922___- ao 22 22 Dec. 19, 1922___ o4 =a —0.5 —0.5 
Aug. 13, 1922____ 20.5 20.5 || Mar. 19, 1923_____ 2 2 
Aug. 14, 1922____ 21.8 21.8 |] Mar. 20, 1923_____ = —il 
Aug. 15, 1922_ 22 22 Mar. 21, 1923__ a ibis 1.5 
Sept. 6, 1922____ 22 22 War 82291925 Sea ROLES SEE as 2 2 
Sept. 7, 1922____ 2 ass 21.4 214 via 2351923 eee eames ewan ne sees ae 0.3 0.3 
Benes 922 = S 2 ae Sas es ee ee 20. 4 20. 4 
GENERAL DISCUSSION OF PLANKTON 
Marine plankton at Woods Hole falls naturally into two great groups—the 
oceanic and the neritic—each of which has quite distinct characteristics. 
The oceanic plankton consists for the most part of adult animals existing 
throughout life as a part of the pelagic fauna. The only immature forms normally 
occurring are the young of these oceanic species. Occasionally larval animals from 
the neritic plankton are blown out in offshore winds, but this does not occur often. 
However, it would be impossible to draw a line denoting the boundary between 
the two types. There exists a broad intermingling area into which each species 
extends to a point where external conditions form a natural barrier. As all forms 
are not subject to the same conditions, this wide intermingling zone results. 
The neritic plankton, in contrast to the oceanic, consists for the most part of 
immature forms which in adult life are not a part of this community. There are, 
of course, many truly pelagic animals common to the littoral zone, but these are 
usually greatly outnumbered by the temporary intruders, except during the winter 
and spring months, when the larval forms reach their minima at the same time 
that many copepods and Sagitte have their maxima. 
Figure 7 illustrates in a general way the constituent parts of the zooplankton 
at Woods Hole at different times during the year. It will be noticed that the 
summer and winter plankton are made up of representatives from the same groups. 
The great difference in the relative abundance of these in the two seasons will be 
discussed later. 
The influx of oceanic species occurs both in summer and winter, although 
the number of different forms occurring in the colder months is comparatively small. 
During the summer, however, swarms often appear. Great masses of Sargassum, 
with its many inhabitants—Physalia and other floating forms—often fill the waters 
of the Sound after a southeast storm or a continued hard wind. Wheeler noticed 
