458 



THE COMMUNITY 



at times more individuals, in a habitat with 

 a mixed substrate than there are in any of 

 the component materials where these latter 

 exist in a relatively pure state. 



The third Httoral type, the mud shores 

 of estuaries and depositing banks, is 

 ecologically much more closely related to 

 the sand littoral than to the rock httoral. 

 Mud shores offer the same shifting substrate 

 as sandy shores, and there are many inter- 

 gradations between the two types. Bur- 

 rowing mussels [Mya, Scrohicularia) and 

 worms {Sabella, Mijxicola) are characteris- 

 tic. Mud snails (Nassa) , boring whelks 

 (Murex), starfish (Asterias), and some ane- 

 mones (Sagartia beUis) are common. This 

 mud littoral is both horizontally and verti- 

 cally stratified. 



Sublittoral Zone 



Seaward of the littoral zone is the 

 second large-scale horizontal stratum. This 

 is the subhttoral zone, generally extending 

 from low-water tide-mark down to the 200 

 meter line. This relatively shallow water 

 region is secondarily horizontally stratified 

 (Russell and Yonge, 1928), in the North 

 Atlantic at least, into several substrata. Near 

 low-water mark, just seaward of the Himan- 

 thalia belt of the rocky littoral, a thick 

 girdle of the seaweed Laminaria is fully 

 developed; for example, L. digitata at low- 

 water mark and L. Cloustoni in slightly 

 deeper waters of the English sublittoral. 

 Where the bottom is more or less sandy 

 these species are supplanted by L. sac- 

 charina (Chapman, 1941). 



The sublittoral bottom is of soft con- 

 sistency and composed largely of sand, 

 mud, and clay in which stones and numer- 

 ous molluscan shells are deposited. The 

 marine and fresh-water sublittorals have a 

 parallel development of a "shell zone." To 

 a depth of 100 to 120 meters there are 

 calcareous seaweeds or nullipores (Litho- 

 thamnion); beyond this depth plant life, 

 except for bacteria, becomes rare. The 

 bottom fauna holds multitudes of Foramini- 

 fera; masses of sponges (Clione) with their 

 secondary inhabitants, e.g., crustaceans and 

 worms; echinoderms, including crinoids, 

 brittlestars, starfishes (Solaster, Porania) , 

 sea urchins and sea cucumbers in variety; 

 colonial coelenterates in thick growths, such 

 as sea fans and sea pens; worms, including 



leathery sipuncuhds, nemertines, poly- 

 chaetes (Chaetopterus) ; crustaceans, as, for 

 example, the Norway lobster (Nephrops), 

 rock lobster (Paliniirus), hermit crabs, 

 spider crabs (Maia), stone crabs {Lith- 

 odes); mollusks, including many whelks 

 (Bucciniim) , boat-shells (including the 

 carnivorous Scaphander), scaphopods 

 (Dentalium), bivalves, such as Cijprina 

 islandica of the North Sea, Spisula, which 

 occurs on the Dogger Bank in patches 20 

 by 50 miles with a population density of 

 1000 to 8000 per square meter, and scallops 

 (Pecten). There are several genera of oc- 

 topi (Eledone, Octopus) and numerous spe- 

 cies of fishes. This extensive fauna, includ- 

 ing both active and sessile benthos, as well 

 as nekton, is primarily engaged in bottom- 

 straining, scavenging, and in carnivorous 

 activities. 



Turning our attention to the European 

 side of the Atlantic Ocean in general, we 

 find that during the present century the 

 sublittoral areas of the North Atlantic have 

 been intensively studied, especially by such 

 Scandinavian investigators as Petersen 

 (1913, flF.). The Atlantic Ocean adjacent to 

 the British Isles, Enghsh Channel, North 

 Sea, Baltic Sea, Kattegat, Danish half of 

 the Skagerrak, and a narrow strip along 

 the western fimbriated coast of Norway 

 are not deeper than 200 meters (Philip, 

 1934). This extensive sublittoral is intruded 

 upon by the deep sea zone off the Norwe- 

 gian coast where deeper water lies near 

 shore and follows narrowly into the Norwe- 

 gian half of the Skagerrak. 



In Danish water there are eight distinct 

 minor communities that have been rec- 

 ognized by Petersen (1914, 1915, 1915a, 

 and 1918). One of these minor com- 

 munities is, properly speaking, a littoral 

 biocoenose, and is exposed at low tide (the 

 Macoma community in the Ringkoebing 

 Fjord). 



Intrazonal stratification of the sublittoral 

 corresponds to similar intrazonal stratifica- 

 tion elsewhere in the major marine com- 

 mvmity, and attests to the general nature 

 of the process. It is found in the narrow 

 sublittoral of northern Norway (Soot-Ryen, 

 1924), eastern waters of Greenland 

 (Sparck, 1933), off Iceland (Sparck, 1929, 

 1937), off Massachusetts (Verrill and 

 Smith, 1874; Alice, 1923a, 1923b), and in 

 the northeastern Pacific in the waters ad- 



