392 BULLETIN OF THE BUREAU OF FISHERIES 



(chiefly Skeletonema and Rhizosohnia alata; pp. 448 and 447) , whereas hauls at several 

 stations farther out in the bay or off exposed stretches of the coast line " were domi- 

 nated by the peridinian genus Ceratium (p. 407), as the open gulf as a whole usually 

 is in summer. 



We also found the water in Casco Bay, near the Harpswell biological laboratory, 

 so cloudy with diatoms and Peridinium with bright red chromatophores on July 27, 

 1912, that its transparency was only about 4 meters. Two days later, however, a 

 tow at the same location yielded hardly a diatom and very little phytoplankton of 

 any kind, its place being taken by a fair representation of copepods, small medusas, 

 and many ophiuran larvae. 



Tows for the years 1912, 1914, and 1915 proved diatoms a major element in the 

 phytoplankton in the neighborhood of Mount Desert Island in August; locally 

 swarming (p. 431). Fritz (1921) also found this to be the case in the St. Andrews 

 region. She also records an abundant July plankton of diatoms in the more open 

 waters of the Bay of Fundy. Our few August tows in the Grand Manan Channel 

 have yielded chiefly diatoms, though the phytoplanktonic community as a whole 

 has been extremely sparse there. Diatoms have likewise shared with the peridinians 

 the domination of our summer tows in the northeastern corner of the gulf off the 

 mouth of the Bay of Fundy, and we have found this condition on German Bank and 

 off Lurcher Shoal during each August when we have visited that region, while there 

 were a few diatoms as far offshore as Browns Bank on July 24, 1914, among the 

 more abundant peridinians that characterized the phytoplanktonic community there. 

 Cape Sable, however, seems to mark the eastern boundary for diatoms as an appre- 

 ciable factor in the plankton during the latter half of the summer. 



Diatoms were a much more important factor in the plankton of the gulf in the 

 summer of 1912 than at that season in 1913, 1914, or 1915. During that July and 

 August they occurred in great abundance all along the coast from Seguin Island 

 (situated a few miles east of Casco Bay) as far eastward as the mouth of the Grand 

 Manan Channel, and were plentiful enough over the whole northeastern corner of the 

 gulf, mingled with the peridinians, to give a distinctive aspect to the catches, instead 

 of being limited to the narrow confines just outlined as the usual bounds to their 

 summer flowerings. More interesting than the unusual abundance of diatoms which 

 characterized that summer is the fact that this was mostly due to a species (Asterion- 

 ella japonica) which has not been found in the offshore waters of the gulf since that 

 time (p. 432). The genera Thalassiosira and Chsetoceras likewise were more wide- 

 spread and numerous in the eastern side of the basin then than we have since found 

 them at that season, reflecting an unusually late continuance of their vernal flowerings 

 (Bigelow, 1914, p. 132). 



This much stress has been laid on the midsummer status of diatoms in the Gulf 

 of Maine because of the very important r61e which this group of microscopic plants 

 plays in the economy of the sea earlier in the season; but when all is said, diatom 

 plankton occupies only a small part of the area of the open gulf during the warm 

 months, as contrasted with the much more extensive area which then supports a 

 typical peridinian plankton dominated by the genus Ceratium. 



"Stations 10G30, 10631, 10632, 10636, 10638, 10640, and 10641. 



