PELAGIC COMMUNITIES 315 



unfortunate failure to recognize the pelagic community proper. The 

 general relations of the various elements of the pelagic community 

 may be brought out for the waters inside the south end of Vancouver 

 Island. This description is, however, handicapped by a lack of in- 

 formation on the food habits of the nekton. 



Plankton. Studies of the diatoms of this community have been 

 made by Gran and Thompson (1930) and Phifer (1933, 1934); the 

 Protozoa have been treated by Eddy (1925, a), and the Crustacea by 

 Campbell (1929, 1930). The last has found all types of smaller plank- 

 ton organisms most abundant at a depth of about 4 meters, including 

 copepods, peridinia, tintinnids, and diatoms. Phifer (1933, 1934) re- 

 ported diatoms most abundant at 10 meters in the Strait of Juan de 

 Fuca. The depth of maximum abundance differs greatly in various 

 localities and on different dates, but is probably always in accord with 

 physical conditions. In Julj^, 1928, two series of four simultaneous 

 water-bottle samples, separated by 20 minutes at slack tide, were 

 taken over each of the two major bottom communities ( Shelf ord et 

 al., 1935:250). Over the sea urchin-triton snail community (Stron- 

 gylocentrotus-Argobuccinum biome) which usually occurs on rela- 

 tively hard bottoms, counts by Gran of collections distributed from 1 

 to 225 meters showed that the maximum abundance of diatoms was 

 at 20 meters. They were about 1/10 as numerous at the surface and 

 1/16 as abundant at 225 meters as at the maximum. The i)lankton 

 over a clam-worm community (Pandora-Yoldia biome) at 28 meters' 

 depth, usually on soft bottom or fine mud, was sampled in a similar 

 manner within an hour. Diatoms were about 10 times as abundant 

 as over the sea urchin-triton community, and the maximum was at 

 10 meters instead of 20 meters. 



An examination of the animal plankton taken in the net-haul made 

 at the same time from bottom to surface over the clam-worm com- 

 munity yielded a few copepods, rotifers, and tintinnids, very many 

 dinoflagellatcs, and various larval stages. Over the sea urchin-triton 

 community, it differed chiefly in the lack of dinoflagellatcs and in the 

 presence of a greater variety of the larval stages. A few Sagitta were 

 taken from the deep water here, but none over the Pandora-Yoldia 

 community. Jcllyfishes abundant during the summer months through- 

 out both the inner and outer waters are: Aequorea forskalea (P. and 

 S.), Phialidiu77i gregarium Hacck., and Thaumantias cellularia Haeck. 

 These, together with less abundant species of Sarsia, Stomotoca, Poly- 

 orchis, and the common ctenophores (Mnemiopsis and Pleurobrachia), 

 make up a great part of the volume of the plankton of midsummer. 

 There is a large seasonal element including many eggs and larval 



