BIOLOGICAL STUDY OF CHESAPEAKE BAY WATERS 
321 
5,700. At 18 meters the following counts were obtained: Area A, 1,400; J, 13,200; 
M, 34,100; the unlettered area, no count, not 18 meters deep; A, 2,100; P, too shal- 
low; and R, 2,600. It will be seen that at 0, 9, and 18 meter depths the highest 
counts were close to the mouth of the Potomac River. On the other hand, at 27 
meters the highest was at area, A; but at 36 meters, again, the highest count was 
near the entrance of the Potomac: Area A, 700; J, 9,500; M, too shallow; the un- 
lettered area, too shallow; L, 7,500; P, too shallow; R, 900. The largest count for 
any area at any depth during the October cruise was 35,800, a surface count directly 
in front of the mouth of the Potomac; and the second largest count, 34,100, was one 
at 18 meters on area M in the middle of the mouth of the Potomac. Again in De- 
cember, 1915, the highest surface count, 15,100, was at area J and the largest deep- 
water count, 22,800, was at area P. Both of these areas are very close to the mouth 
of the Potomac River. It must be mentioned, however, that the counts for Decem- 
ber are much fewer in number than those for October. The data for the rest of the 
cruises are insufficient for purposes of comparison. 
The vertical distribution of Skeletonema costatum during October, 1915, seems to 
have been largely independent of the degree of salinity, although, as a general rule, 
the highest counts were below the surface and above the bottom. A very interesting 
comparison of the vertical distribution of this diatom at areas A, J, L, and R during 
October may be seen in Table 12. The samples for A (near Cape Charles City) were 
collected on October 22 from 3 to 4 p. m.; those for J (a little south of the mouth of 
the Potomac) on October 24 from 10.30 to 12 noon; those for L (a short distance 
north of the mouth of the Potomac) on October 25 from 9.49 to 10.38 a. m.; and 
those for R (about half way up the bay) on the same date from 1.50 to 3.08 p. m. It 
will be seen that the highest count for area A was in deep water, 27 meters; for J at 
shallower depth, 18 meters; for L, at 9 meters; and for R at the surface. 
Table 12. — Skeletonema costatum, October, 1915 
Meters 
A 
J 
L 
R 
Meters 
A 
3 
L 
0 ... 
600 
200 
1, 400 
4, 300 
6,700 
13, 200 
4,200 
10,500 
2,100 
25, 800 
5,700 
2, 600 
27 „ 
10, 400 
700 
800 
100 
9, 500 
4,400 
7, 600 
9 
36 
18 
46 
A similar condition, although not so marked, was seen for some other neritic 
diatoms collected at the same time. The true bottom forms, on the other hand, 
which do not multiply to any extent in the plankton, did not show the vertical dis- 
tribution just mentioned. It is not permissible to draw any definite conclusions as to 
the factors involved in bringing about the vertical distribution of Skeletonema costatum 
during the October cruise, especially since no counts approaching these in complete- 
ness were made during any other cruises, but it may be mentioned that during the 
time from October 21 to 25 the air temperature at Baltimore and Washington, accord- 
ing to the United States Weather Bureau, dropped from 64° F. (17.8° C.) to 42° F. 
(5.6° C.) and 37° F. (2.8° C.), respectively. One might suspect that there had been 
an increase in the viscosity of the water in the northern part of the bay due to the 
large drop in air temperature, which resulted in a greater buoyancy of the water and 
an upward movement of the diatoms. If such a movement toward the surface actually 
occurred at area R, and to a lesser degree at L and J, we have no evidence to show that 
it was in response to differences in the turbidity of the water, to differences in food 
