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 

 cateh 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, the}' 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 



