22 BULLETIN OF THE BUKEAU OF FISHERIES 



summer Euthemisto is to be expected in abundance over Browns Bank, largely 

 replacing the copepods there, for on July 24, 1914 (station 10228), the surface waters 

 were alive with them, while on June 24, 1915 (station 10296), the tows on the bank 

 yielded large numbers of these amphipods among the still more abundant Calanus 

 (more abundant in bulk as well as in numbers). Euthemisto is also an important 

 factor in the plankton close in to the land off Cape Sable, where they increased in 

 relative abundance in 1914 from July 25 (station 10230), when they were overshad- 

 owed by Calanus, until August 11 (station 10243), when they were dominant in the 

 plankton. A seasonal change of the same sort took place in the shoal coastal waters 

 off Shelburne, Nova Scotia, during the summer of 1915; for Euthemisto dominated 

 a very scanty plankton there on September 6 (station 10313), where it had been out- 

 bulked both by copepods and by Sagittse on June 23 (station 10291), though domi- 

 nating the plankton farther out over the shelf on that day (10293). 



Although euphausiid shrimps of one species or another (p. 133) are practically 

 universal within the gulf — may, indeed, be constantly plentiful locally, as off the 

 Eastport-Grand Manan region, and temporarily so elsewhere (p. 133) — we have never 

 found them dominating the water of the gulf at any level except over Browns Bank, 

 where the tow net working at 60 meters depth yielded a quart or more of these pelagic 

 shrimps 11 on July 24, 1914 (station 10228), diversified only by an occasional Sagitta, 

 three Bero'e cucumis, a few copepods, and no amphipods at all, notwithstanding 

 the abundance of the latter at the surface at this same station. Though not strictly 

 within the limits of the gulf, I may add that four days later euphausiids occurred 

 in great numbers over the slope abreast of Cape Sable 12 (station 10233), and in this 

 same general region on March 19, 1920 (station 20076, fig. 21). It is not safe to assume, 

 however, that these shrimps are constantly abundant over Browns Bank in summer, 

 for we found none at all there on our only other visit during the warm half of the year 

 (June 24, 1915, station 10296), but in their stead made a very rich haul of calanoids 

 (3 to 4 liters bulk), with a few Euchasta, many large Euthemisto, small Sagittae, 

 and occasional tropical organisms, such as Phronima and Salpa zonaria. 



To close this brief survey of the chief planktonic communities of midsummer, I 

 must remark that a sprinkling of Gulf Stream animals — sometimes, indeed, a typi- 

 cally tropical plankton — is to be expected all along the upper part of the continental 

 slope at that season, corresponding to the high temperature of the Gulf Stream, 

 the inner edge of which lies but a few miles farther offshore. This tropical plankton 

 and such members of the general bathypelagic community of the Atlantic basin 

 as approach the slope are the subject of a later section (p. 53) . 



The accompanying photographs (figs. 10 to 21), illustrate certain of the more 

 characteristic communities as they occur in nature, and the distribution of the more 

 characteristic communities, for July-August, 1914, is outlined on the chart (fig. 22). 



The great majority of the species of pelagic animals that unite to form the 

 bulk of the zooplankton of the gulf are endemic in origin, breeding sufficiently 

 regularly and abundantly within its limits to maintain the local stock by local pro- 

 duction. This generalization, which the reader will find discussed in more detail 

 under the accounts of several of the species concerned, applies to most of the com- 



11 Chiefly Afeganyctiphanes norvegica, Thysanassa inermis, Th. longicaudata, with fewer Th. gregaria and Nematoscelis megalops. 

 " Chiefly Euphausia and Nematoscelis and fewer Th. longicaudata at 100 meters; Nematoscelis at 400 meters. 



