318 
BULLETIN OE THE BUREAU OF FISHERIES 
The degree of dependence of diatoms on the salinity of the water has long been 
an unsettled question. Naturally, one would seek for light on the subject in regions 
where there is a distinct stratification with reference to salinity — that is, where there 
are considerably fresher layers overlying much more saline layers. The Baltic Sea, 
which is flooded now and then by saline water from the ocean and by fresh water 
from rivers; the Arctic and Antarctic Oceans, which have a surface layer of fresher 
water arising from the melting polar ice; estuaries such as are found in England; 
the fjords of Norway and Sweden; and finally the mouths of large rivers where 
fresh water and saline water meet one another, have been investigated by ascertaining 
the salinity at various depths from surface to bottom, together with the diatom 
counts at the same depths. If there is a horizontal distribution of diatoms with 
reference to salinity as indicated by geographical studies, one would expect a vertical 
distribution correlated to some extent with the salinity gradient from surface to 
bottom. But the problem is complicated by other possible factors — differences in 
temperature, light intensity, and amount of nutriment at various levels, with the 
accompanying reactions to these differences. Also water currents produced in 
various ways often tend to disturb the relation which the diatoms might usually 
bear toward salinity. 
However, some investigators have found the number varying with the salinity 
in regions where the temperature and light did not seem to be controlling factors. 
Apstein (1906), in his studies of the waters of the Baltic Sea, discovered that many 
Chaetoceras, Rhizosolenia, Cerataulina, and Guinardia species of diatoms occurred 
only on the western side of the Baltic where the salinity was more than 15 per mille 
while Chaetoceras danicum and bottnicum were confined mainly to the east side, where 
the salinity was much weaker. Biise (1915) found the currents entering Kiel Bay 
from the west generally richer in diatoms and of a higher salinity than those coming 
from the east. 
One would look for such relations near the mouth of Chesapeake Bay, as, for 
example, along the line made by areas A, B, C, D. At D on the west side of the bay, 
the fresher water is found, while at area A on the east side, where the depth is much 
greater, the more saline water of the ocean finds its way. The numbers of individuals 
of different neritic and oceanic species should be compared with the salinities at 
these areas. Unfortunately, the data on separate species are insufficient for such a 
comparison. Total diatom counts, however, at the surface for these two areas as 
compared with the salinities are of interest. 
Table 11. — Surface diatom counts and salinity for 1920 
Area 
January 
July 
August 
October 
December 
Diatoms 
Salinity 
Diatoms 
Salinity 
Diatoms 
Salinity 
Diatoms 
Salinity 
Diatoms 
Salinity 
A 
16, 500 
14, 700 
23.32 
19.74 
8, 300 
7, 400 
21. 72 
17.28 
14, 400 
900 
22.36 
19.48 
21, 300 
5, 700 
21. 99 
17.31 
418, 400 
28,300 
22.78 
21.51 
D 
It is clear from data obtained for the cruises of January, July, August, October, 
and December during 1920 that the more saline surface water along the line A, B, C, D 
was found on the eastern side of the bay— that is, at area A. The total surface diatom 
counts were higher, on each cruise, at area A than at area D, which is on the west side 
