COMMUNITIES OF THE SEA BOTTOM 331 



being the very large Stichopus californicus Ed., and pectens are often 

 abundant. 



The motile influents include fishes and crabs of the genera Hyas, 

 Cancer, Orcgonia, and shrimps of the genus Pandalus. Of the most 

 regularly occurring fishes are the northern sculpin {Icelinus borealis 

 Gibb), the giant sculpin {Myoxocephalus polyacanthocephalus 

 [Pall.]), and the grunt fish {Rhainphocottus richardsoni [Gunther]). 

 There are also various crabs, shrimps, gastropods, and starfishes, all 

 of relatively large size. 



Subdivisions. The major community is divisible into two sub- 

 ordinate connnunities in accordance with depth. Tlie first ranges from 

 the surface to 35-50 meters and the other from 35-50 to 225 meters, 

 or even deeper. 



Green Sea Urchin-Kclpcrab Community {Strong ylocentrotus-Pu- 

 gettia Association) . The biome building influents already enumerated 

 occur throughout and make up a considerable part of the population. 

 The large echinoderms, Stichopus californicus and Strongylocentrotus 

 franciscanus, are abundant and conspicuous in this association and 

 very few in the one in deeper water. Two other cucumbers, several 

 snails, and limpets occur in noteworthy abundance. Various fishes 

 such as rock fishes (Sebastodes), several sculpins, but particularly the 

 blennies, frequent the shallow waters. There are also numerous char- 

 acteristic Mollusca. This association is characterized by algae, both 

 red and green. They are usually irregularly distributed and do not 

 have a marked effect on the animals present. They are hardly to be 

 classed as dominants, but since they occur over only a portion of the 

 bottom, the areas which they cover are best regarded as faciations. 

 A faciation of INIelanophyceae occurs between mean low tide and 

 depths of 15 to 20 meters, and those of Rhodophyceae mainly be- 

 tween depths of 10 and 20 meters, only a very few small animals 

 being characteristic of the latter. Other faciations occur where the 

 bottom soil differs ; thus on mud bottom two or more of the numerous 

 Strongylocentrotus-Pugettia prevalents drop out and Cardium cali- 

 fornense Desh., Yoldia scissurata Dall, and other species of similar 

 habits take their places. The community otherwise retains its biome 

 and association prevalents (see Andrews, H. L., 1925; and Andrews, 

 F. B., 1925). 



Green Sea Urchin-Cushion Starfish Community [Strong ylocentrotus~ 

 Pteraster Association) . This occurs below 35-50 meters and down to 

 at least 225 meters; the species characteristic of the Pugettia associa- 

 tion either become scarce or drop out. Several large showy echino- 

 derms take their places; these are notably the cushion star [Pteraster 



