484 BULLETIN OF THE BUREAU OF FISHERIES 



bottom throughout the season in the Grand Manan Channel and locally in the Bay 

 of Fundy. 



These several factors unite to make the coastal zone east of Penobscot Bay on the 

 whole a more favorable environment for diatoms in summer than any other part of the 

 gulf except Georges Bank, to be discussed later (p. 4S5). Since this theoretic 

 generalization corresponds with the quantitative distribution of diatoms as actually 

 observed during the warm months, the factors just mentioned are probably the chief 

 ones which explain the persistence of rich flowerings of diatoms in abundance in the 

 Mount Desert region and in Passamaquoddy Bay throughout the summer, con- 

 trasted with their exhaustion in the Massachusetts Bay region by early May. I 

 have not been able to trace the dependence of particular flowerings on physical 

 or chemical conditions in the sea water more closely than this. 



Our failure to find diatoms in as great abundance between Mount Desert Island 

 and Grand Manan as the flowerings farther west, on the one hand, or those reported 

 by Fritz (1921) at St. Andrews at the mouth of the St. Croix River, on the other, is 

 puzzling, for this section of the coastal zone not only receives a considerable influx of 

 land water from several streams that may be expected to be rich in dissolved food- 

 stuffs, but there is a dominant outflow along it from the Bay of Fundy. 



No part of the gulf becomes uninhabitable for diatoms even when the water 

 becomes warmest and most stable and flotation most difficult. On the contrary, 

 certain species then reach their maximum development, as an example of which the 

 summer flowerings of Asterionella and Skeletonema will serve (pp. 431, 448). The 

 latter, as it occurs in Massachusetts Bay, is especially interesting because the dates 

 when an abundance of Skeletonema has been recorded in 1915 and 1922 (early 

 autumn and late summer, respectively; p. 476) follow so closely the rise in the con- 

 centration of silica recorded for late June in 1921 (fig. 134) as to suggest that it is the 

 accumulation of silica taking place during the late spring and early summer (when 

 there are few diatoms in that region) which makes the water there able to support 

 the autumnal flowerings of Skeletonema. 



The general scheme of circulation in the gulf (with the water from the rivers 

 tending to swing westward and to hug the coast line during most of the year, as 

 shown by the distribution of salinity) is a sufficient explanation for the fact that the 

 vernal flowerings of diatoms of its inner parts appear first close in to the land and 

 attain a greater abundance and endure longer there than over the deep basin. The 

 contrast in this respect between the coastal zone and the offshore banks, on the one 

 hand, and the central deeps of the gulf on the other, simply reproduces on a small 

 scale that between coastal or neritic waters and more oceanic regions in general. 

 The gradual expansion of the diatom flowerings offshore from the land out over the 

 central part of the gulf, where it does not reach its maximum until early May (p. 388), 

 follows the offshore dispersion of the spring freshets of land water with their load of 

 nitrogen, phosphorous, and silica. 



It is in just such areas as the open basin of the Gulf of Maine, where the tran- 

 sition from a state of free vertical circulation in early spring is sudden to one of very 

 pronounced vertical stability in summer, when the supply of nitrogen and of phos- 

 phates from the deeps is thereby prevented, and where the silica content of the 



