BIOLOGICAL STUDY OF CHESAPEAKE BAY WATERS 
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The highest diatom count for all of the cruises of the year 1920 was 1,563,000, 
and this was found in March, 1920, at area L close to the mouth of the Potomac and 
at the bottom. On the other hand, the second largest count, 1,055,400, was found 
at area B in a sample taken at the bottom in March, 1920. This area is situated 
close to one of the deepest holes in the bay and near Cape Charles City, which is 
located on the shore of the bay within a few hundred yards of the area. 
The evidence in support of the theory that the highest diatom counts are to 
be found in the neighborhood of the mouths of rivers is not conclusive, and yet there 
are indications that there may be such a relation. Undoubtedly a study of the 
distribution of each species of diatom rather than a mixture of fresh-water, semi- 
bottom, and marine diatoms, such as is found in total diatom counts, would be more 
satisfactory. Some of the evidence we have from this source will now be mentioned. 
It will be discussed later. 
The data concerning the abundance of the different species of diatoms at surface, 
bottom, and uniform intermediate depths are limited to the cruise taken in October, 
1925. One species, Skeletonema costatum, which lives as a littoral-bottom form to 
some extent but which also exists as a widely distributed plankton form in Chesa- 
peake Bay, is of interest in this connection. It will be shown later under the section 
in which the distribution of S. costatum with reference to hydrographic data is dis- 
cussed that this diatom during the cruise of October, 1915, was more abundant, 
except at 27 meters, in the region of the mouth of the Potomac River than at any 
areas investigated. 
DIATOM SCARCITY AT MOUTH OF BAY 
The diatom counts in the mouth of the bay were usually comparatively small. 
Such a condition might be expected, since it is a shallow region with a shifting bottom 
which at times is scoured by rather rapid currents. It is a well-established fact 
that such places are not favorable for the development of diatoms. The highest 
count recorded in the mouth of the bay during the years 1916 and 1920 was a surface 
count of 438,800. This number was found at area F during April, 1916, along the 
line E, F, G, which extends across the mouth of the bay. Even at this time, which 
was during the spring maximum, there were higher counts along the line A, B, C, D, 
which runs from Cape Charles City to New Point Comfort. The records show 
558,300 (surface) at A and 3,157,200 (bottom) at D. 
RELATION OF DISTRIBUTION OF DIATOMS TO SALINITY 
It is well established from a study of geographical distribution that certain 
diatoms (oceanic) are characteristic of waters of high salinity, such as that of the 
open ocean; that others (neritic) are characteristic of waters of lower salinity found 
along the sea coast and in estuaries; and that still different ones frequent the fresh 
waters or rivers emptying into the ocean. But, also, it is well known that many 
of these diatoms are able to stand a large range of salinities and that oceanic as 
well as neritic diatoms are often found in estuaries where the salinity is very low. 
The assumption is that the oceanic forms as well as neritic forms are brought in with 
the currents from the ocean, but it is known that resting spores are formed in the 
latter type. It is believed by many investigators, especially by Gran, that these 
spores settle to the bottom of the estuaries and periodically assume the floating 
condition, so that there are supplies from year to year of certain neritic species 
which arise locally. 
