COMMUNITIES OF THE SEA BOTTOM 333 



shallow- water communities 

 (habitat partially exposed at high tide) 



Macoma-Paphia Biome 



In the Pugct Sound waters (North Pacific), this biome is usually 

 found well developed between 8 meters below and 1 meter above mean 

 low tide (the tidal amplitude being 3 and 4 meters). There are about 

 2 meters of true ecotone between 8 and 10 meters' depth and the com- 

 munity thins out to nothing between 1 and II/2 meters above mean low 

 tide. Clams of four species, Macoma nasuta Con., secta Con., inqui- 

 nata Desh., and Paphia staminca Con., usually make up the great 

 bulk of the population. The clam worm. Nereis virens Sars., is also 

 a regular constituent. Several other species of bivalve mollusks al- 

 ways occur, but in varying numbers. The most important motile in- 

 fluents are several species of flounder (especially Psettichthys melan- 

 ostictus [Gir.] and the tide-pool sculpin {Oligocottus maculosus 

 [Gir.]) (cf. Fraser and Smith, 1928, a, b). 



Two subdivisions or associations have been recognized, of which 

 the Macoma-Paphia association fits the general description of the 

 biome. The second association (Macoma-Leptosynapta) possesses 

 the same constituents but in different abundance. The butter clam 

 {Paphia staminea) is much less, the cockle {Cardium corbis Mart.) 

 much more, abundant. The lugworm (Arenicola claperedii Lev.) and 

 the wormlike cucumber {Leptosynapta inhaerens Ver.) take the place 

 of various smaller worms of the other associations. 



Both associations are characterized by eelgrass, usually in re- 

 stricted areas representing depth belts. The eelgrass is quite impor- 

 tant and supports algae, numerous crustaceans such as Caprella, large 

 amphipods, isopods, and snails such as Haminoea and Lacuna, espe- 

 cially in the Macoma-Paphia association. In the Macoma-Lepto- 

 syapta association the additional species are more numerous, and in 

 some cases sand dollars are abundant locally (Shelford et al., 1935). 

 The importance of eelgrass has been brought out by Petersen and 

 associates and will be discussed later. 



The Pacific oyster evidently represents a fragmented faciation in 

 the southern part of this community, which with overfishing was com- 

 pletely destroyed by the burrowing and earth moving of the large 

 crustacean, Upogebia. The communities of the northeast Atlantic 

 and adjacent Arctic which are similar to Macoma-Paphia community 

 in life forms and position relative to tidal levels have been studied, 

 but their rank in terms of biome and association can only be sug- 

 gested and may prove incorrect. 



