404 
BULLETIN OF THE BUREAU OF FISHERIES 
produce a flora at all comparable in abundance to the diatoms which it succeeds. As 
a rule, indeed, the Ceratium plankton of midsummer has seldom yielded volumes much 
larger than 25 cubic centimeters, rarely as much as 40 cubic centimeters except when 
fortified by diatoms, or by Acanthurian radiolarians, as was the case off Cape Ann in 
August, 1914 (p. 460; Bigelow, 1917, p. 324). Occasionally, however, Ceratium occurs 
in greater abundance — for example, on August 13, 1912 (Bigelow, 1914, p. 131), when 
“ we were struck by the slick, oily appearance of the water some 35 miles off Cape 
Elizabeth, and consequently stopped the vessel for a surface tow (station 10026b). 
The net, when brought aboard, was distinctly reddish, and its meshes clogged with 
what proved to be a mass of Ceratium, * * * and this phenomenon continued 
for several miles.” It is not unlikely that a swarming of Ceratium was reponsible for 
a streak of white water 65 to 75 miles long and 30 to 40 miles wide reported off 
Monhegan Island in 1882 (Collins, 1883, p. 282). But such events as these are quite 
exceptional for the Gulf of Maine, our subsequent cruises having shown that 1912 was, 
generally speaking, a very "rich” summer for Ceratium as well as for diatoms. 
With our standard net and time of towing, 50 cubic centimeters would be a very rich 
catch of Ceratium for the gulf, whereas 10 times as much as this is nothing remarkable 
for diatoms during the period of their greatest abundance. Neither do the local 
swarms of Acanthometron, which are sometimes met with in the western part of the 
gulf in midsummer (p. 460), produce any such abundance of organic matter as do the 
diatoms; at the greatest, they have raised the volume of the catch to 70 or 80 cubic 
centimeters, as was the case off Cape Ann on August 12, 1914 (station 10253). 
In summer, as a general rule, the greatest volumes of phytoplankton are to be 
expected in the coastal zone east of Penobscot Bay, especially over the small area near 
Mount Desert Island, where diatoms usually persist in numbers right through the 
season into autumn. But this productive area does not extend westward past Pe- 
nobscot Bay, on the one hand, nor more than a few miles eastward past Mount Desert 
Island, on the other. July and August hauls near the coast off the mouth of the 
Grand Manan Channel and in the latter itself have been decidedly barren. Local 
swarms of diatoms may also produce an extremely abundant phytoplankton in July 
on Georges Bank (p. 391). In other parts of the gulf, where the abundance of the 
summer phytoplankton, or the reverse, depends on the numbers of Ceratium locally 
present, no division into “rich” and “barren” areas is yet possible, for our large 
hauls of peridinians have been at widely separated localities in different summers. 
Thus in 1912 our richest hauls of Ceratium (the largest we have ever made) were 
off Cape Elizabeth, as just noted; off Cape Cod in July, 1913, and July, 1916 (stations 
10057 and 10058, Bigelow, 1915, p. 334; station 10345); and near Lurcher Shoal in 
August, 1914 (station 10245). On the whole, the deep offshore waters of the gulf 
have always proved decidedly barren of phytoplankton in midsummer, contrasted 
either with these Ceratium centers or, more markedly, with the diatom flowerings 
of the coastal waters. 
In the Massachusetts Bay region the September flowering of Skeletonema is 
reflected in the amount of phytoplankton taken in the nets, as might be expected, 
raising the volume to some 25 to 30 cubic centimeters on September 29, 1915 (station 
10320), when this diatom formed the bulk of the catch, contrasted with a volume of 
