BIOLOGICAL STUDY OF CHESAPEAKE BAY WATERS 
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usually increase from the surface to the bottom. It seems to be a bottom form 
which is easily disturbed from its resting place. 
The following tychopelagic forms were widely distributed in the bay but the 
counts made were not large: Actinoptychus undulatus (Kuetz) Ralfs., Hyalodiscus 
stelliger Bail., Navicula bombus (Ehr.) Kutz., N. cancellata Donk. Other tychopelagic 
forms occurred in very small numbers and had a very limited distribution in the 
plankton so far as the data for 1916 show. Actinoptychus splendens (Bail.) Ralfs. 
was found near the mouth of the bay only at areas A, G, and F and Donkinia recta 
at area G only. 
The neritic arctic group is represented by one species, Biddulphia aurita (Lyngb.) 
Breb. While it was found to be common in bottom samples off the mouth of the 
Delaware River by Mann, it was collected from the plankton on one occasion only 
in Chesapeake Bay during the year 1916. It was in a surface sample at area A near 
the mouth of the bay. The sample was taken during the month of March in water 
of 3.1° C. temperature and 24.14 salinity. 
Of those diatoms which have been included under the neritic north temperate 
group only two species, Rhizosolenia setigera Brightw. and Skeletonema costatum 
(Grev.), were widely distributed in Chesapeake Bay. The records for R. setigera 
show that it occurred most abundantly from the mouth of the Potomac River to the 
mouth of the bay, and that the highest counts were obtained during the autumn and 
spring cruises (October, 1915, and April, 1916), indicating autumn and spring maxima. 
The counts in the region of the mouth of the Potomac were not any larger than those 
lower down the bay at area A. The distribution of this species in the Chesapeake 
shows that it can stand considerable variation in salinity and temperature, but it is 
of interest to note that above the mouth of the Potomac it was not recorded as having 
occurred in the surface layer. The data are not complete enough to admit of any 
conclusions as to the vertical distribution. A discussion of the distribution of &. 
costatum has been taken up above. Other species included in the neritic northerly 
temperate group — namely, Thalassiothrix nitzschioides Grun., Nitzschia longissima 
(Breb.) Ralfs., Chaetoceras teres Cl. and Leptocylindrus danicus Cl. — were not repre- 
sented by large numbers in the bay, although T. nitzschioides was found as far north 
as area R in October (16.49 per mille, 17.3° C.) and N. longissima as far north as the 
same area in June (approximately 17.00 per mille, 17.2° C.). 
The most abundant diatom of the neritic southerly temperate group during the 
1915 and 1916 cruises was Cerataulina bergonii Perag. The high counts of the April, 
1916, cruise at areas A, J, L, and X as compared with the numbers found on other 
cruises indicate a marked spring maximum. The minimum occurred in the summer, 
judging from the surface records of the July cruise. At area A during the April 
cruise the surface count was 407,200 (18.46 per mille, 11.4° C.), at J, 65,400 (10.81 
per mille, 12.1° C.); at L, 40,400 (12.05 per mille, 11.0° C.); and at X, 5,200 (5.88 
per mille, 9.4° C.). The deep-water count for A at 27 meters was 300,800 (no salinity 
record, 10.5° C.); for J at 27 meters, 353,800 (no salinity record, 8.8° C.); and for L 
at 26 meters, 173,200 (17.63 per mille, 8.9° C.). No deep-water count was made at 
X. It is evident from the records that the largest numbers of C. bergonii were found 
in samples from the lower half of the bay, especially at area A and the areas near the 
mouth of the Potomac River. The records for this diatom and those which follow 
are insufficient for a consideration of the vertical distribution. Rhizosolenia calcar 
avis Schultze, which I have placed provisionally in the neritic southerly temperate 
1988—30 4 
