PLANKTON OF THE GULF OF MAINE 385 



the 23d of that month in 1920 (stations 20078 and 20082 to 20085), it consisted chiefly 

 of diatoms with few peridinians; and by April 15 (stations 20101 and 20103 to 20106) 

 the waters in this part of the gulf were cloudy with neritic diatoms of the species 

 listed below (p. 427). A rich diatom community was also discovered by the Albatross 

 on the southwestern part of Georges Bank even earlier in the year (February 22, 

 station 20046). 



The diatom flowerings of the western side of the gulf expand in all directions 

 and at the same time multiply so rapidly during the last half of March that their 

 numbers are soon countless. By the 3d of April we have found them so abundant 

 in Massachusetts Bay as to cloud the water and clog our nets (Bigelow, 1914a, p. 405) , 

 a state again observed from the 6th to the 9th of April in 1920 (stations 20089 and 

 20090) ; and by that season diatoms swarm from Cape Cod on the south to Cape 

 Elizabeth and Casco Bay on the north, as far out from land as the 200-meter contour 

 at the inn er edge of the western basin (fig. 105). Fritz also found diatoms aug- 

 menting suddenly and to an extraordinary abundance at St. Andrews between the 

 end of March and the end of April. Meantime the eastern diatom community 

 vastly augments in numbers over the whole coastal bank off southwestern Nova 

 Scotia and out across Browns Bank to the eastern channel (stations 20103 to 20107), 

 where we found them swarming on April 12 to 16 in 1920. 



A rich gathering of diatoms off the southeast slope of Georges Bank on that 

 date (station 20109) is especially interesting because there were comparatively few 

 (and these of more oceanic species) in the waters over the neighboring parts of 

 the bank (stations 20108, 20110 to 20111). The presence of the abundant 

 flowering in question at just that place therefore points to a drift from Browns and 

 the other shallows to the eastward, as did a shoal of Calanus at that same locality 

 the month previous (p. 189). However, Georges Bank is itself the site of extremely 

 productive flowerings in April, though we did not chance to encounter them there 

 in that month in 1920, for Douthart's tows yielded a great abundance of several 

 species on its northern part during the last half of the month in 1913 (Bigelow, 1914a, 

 p. 415). 



Hand in hand with this vernal multiplication of diatoms, peridinians diminish 

 almost to the vanishing point. As the impoverishment of this group apparently 

 takes place nearly simultaneously over all but the southeast corner of the gulf, and 

 so early in the season that the rich diatom flowerings are still restricted to the coastal 

 waters within the gulf, to the shallows of Browns and of Georges Banks, and to the 

 intervening channel and the continental slope, there is a very sharp contrast during 

 the last half of April between these swarms of diatoms and a very scanty diatom 

 plankton in the central and northeastern deep of the gulf, which is reminiscent of the 

 mixed peridinian and diatom community existing there in March. 



During late April the flowerings of diatoms that have originated in the north- 

 west part of the guff two months earlier (fig. 104) spread eastward beyond Mount 

 Desert Island, while at about this same time a great increase takes place in the 

 numbers of diatoms (though of other species) present in the waters of the Western 

 Basin 24 and thence throughout the center of the gulf generally, where we found 



••In 1915 diatoms were extremely abundant in the Western Basin and near Cashes Ledge on May 4 (stations 10267 and 10268, 

 fig. 121) 



