106 BULLETIN OF THE BUREAU OF FISHERIES 
It is of extreme importance in ocean waters, however. Food material is the domi- 
nant governing factor for all diatoms. The supply of the substances not common 
to all sea water arises from two sources—outwash from the land and the replacing 
of chemicals by the breaking down of the organic substances in the sea. For this 
reason diatoms are much more abundant in the coastal waters, particularly near 
the mouths of large rivers (Table 3). No doubt the large amount of disintegrating 
material often found in coastal water (Bigelow, 1914) after a diatom decline forms 
an important item in the replacement of essential chemicals such as silicic acid and 
nitrates, but in comparison with the source of supply from the land it must be 
rather small. Conversely, in the open ocean it probably forms the most important 
source in regions where the land areas exert little or no influence. In this respect 
the oceanic and coastal conditions are widely different. 
TaBLE 3.—Disiribution of diatoms in Long Island Sound in early March, 1923. Volume determined 
from vertical hauls 
Locality Date | Volume | Depth 
(8505 Meters 
MPnTOgS RN GCE er seeter eet Hee Se ee ease eNe 22d Aa eee ee em Mar. 5 4 5 
Hempstead Harbor_ A Edn 6 5 
Matinicock Point__- idol 2.5 5 
Cold Epune Harbor 2.5 5 
Pecks Ledge________ 4.5 5 
Pine Creek Point_____- a 4 5 
Off Bridgeport Harbor-------- Bes Lae Riek rae a Base 8 5 
Stratfordjront eee oe aie —_ a Eee 20 5 
Housatonic River, near breakwater_ Redo 12 5 
New Haven\iHarboro.) = 92-22 ote a oh nee 2 ee a ae do 10 5 
Stations inside of Harbor No. 1__- Mar. 7 8 5 
Stations inside of Harbor No. 2___ Laidol= 6.5 5 
Stations inside of Harbor No. 3__- edo 6.5 5 
Bive-fathomenOck es mae it Geek Tree ee et ee eae a ee ee ee ee |e do-___- 7 5 
Sachem Head-_-_-___ _-do_- 10.5 5 
ammonasset Point _-do__ 8.5 5 
Falkner Island _-- dos 2 5 
Gardiners Bay--- Mar. 8 5 5 
Little Peconic Ba’ .-do_ 1 5 
Hortons Point_-__ me dows 4.5 5 
HMAtOMMRO Iter see eee ee oe ee ee Mar. 9 3.3 5 
iMid-Sound positions 40-59-o4N7i/o~23—1 On Wie eee nee oe anne eee aaa _-do. 4 5 
In the ocean, where uniform physical conditions often exist to comparatively 
deep water, Nathansohn (1909) found that the diatoms are most abundant in localities 
where the greatest amount of vertical circulation takes place. (Gran, 1912, gives 
maximum abundance often as deep as 50 meters and large numbers at 100 meters.) 
Large quantities of organic material are constantly sinking to the deeper water, 
and the decomposition of dead plants and animals at these levels sets free the nutri- 
tive substances, which are returned to the photic zone in the ascending currents. 
In anticyclonic systems like that of the Sargasso Sea, where little or no vertical cir- 
culation takes place, the diatoms were found to be very scanty. Nathansohn’s (1909) 
theory, no doubt, does not apply to all conditions found in the sea, but remains as 
the best explanation of the source of production of oceanic diatoms. Ocean currents, 
which themselves change according to the seasons, cause the diversity of high sea 
plankton in fixed geographical positions. The occurrence of certain species far 
beyond the limits of their natural range is usually attributed to currents. 
In the coastal waters an entirely different condition of affairs exists. Over the 
deeper parts of the neritic zone plant life usually is limited to a very thin surface 
