336 MARINE BIOTIC COMMUNITIES 



built up on the shoreward side of this faciation just as on protected 

 beaches of the North Atlantic. 



The Zostera-Rissoa-Cardium faciation, in which burrowing species 

 remain the same, is characterized by a large addition of forms that 

 attach to or hide in the Zostera. Small snails belonging to five spe- 

 cies, and numerous crustaceans, including small representatives of all 

 the higher groups, crowd the surface and interspaces of the Zostera. 

 The Crustacea are especially important to fishes; some five or six 

 kinds of small fishes, including several of gobies, feed upon them and 

 in turn are eaten by cod (Gadus callarias) . The sea scorpion competes 

 with the young cod, as both live largely on the Crustacea. The vivi- 

 parous blenny, the young of the eel, and the flounder also feed in the 

 Zostera. The cod leave these habitats when the juvenile stages are 

 passed and feed mainly in other communities, although schools of 

 adult cod from the north come in to the Zostera belt in autumn and 

 feed on the great variety of foods (cf. Ostenfeld, 1908). 



In addition to the two faciations discussed, the IMacoma-Asterias 

 faciation occurs outside the Zostera belt in deeper water. The same 

 characteristic dominants occur and in addition large crabs, gastro- 

 pods, and starfishes. Most of the fishes of the Zostera faciation are 

 to be found here. The cod, plaice, and dab are only visitants. 



Extent and Variations. Two and perhaps three associations are 

 suggested. A Macoma-Tellina association, which Sparck (1935) con- 

 siders a different community, occurs in the Kattegat on low open 

 sandy coasts exposed to strong wave action (see Blegvad, 1916:54). 

 It appears to correspond to the Macoma-Paphia biome in the North 

 Pacific. There are communities of this type also on the Atlantic 

 coast of North America (cf. Newcombe 1935, a, b) , for example Alice's 

 (1923) sandy bottom community in the Wood's Hole area (cf. Sumner, 

 Osburn, Cole and Davis, 1911). 



The importance of Zostera in this community as a source of detri- 

 tus has been stressed by Petersen and Lewisohn (1899), Petersen 

 (1913, 1914, 1915 a, b) . Blegvad (1914) has found that the non- 

 predatory bottom-inhabiting species of this type, and of strictly sub- 

 tidal communities of the same type, feed upon detritus. He has 

 classified most of the slow-moving dominants as detritus-eaters or 

 predators. The larger and more motile influents commonly feed upon 

 the bottom detritus-eaters. In the enclosed waters east of Denmark, 

 the contact of the Macoma-Mya biome is, with the northern com- 

 munities, characterized by Syndosmya, Fig. 76 (Peterson's Abra Com- 

 munity) which is probably an ice-age relict. 



The oyster communities to which Mobius (1877, 1883) applied the 



