American Fisheries Society 213 



mals, being composed almost exclusively of diatoms, unicel- 

 lular algae, infusorian protozoa, small medusae, copepods, 

 and the eggs and larvae of other littoral forms. The unicel- 

 lular algae and diatoms are especially abundant, and in the 

 neighborhood of river mouths much fresh-water plankton 

 is added, as well as masses of minute particles of decaying 

 organic material. The richness of this plankton as food 

 material is well brought out in James Ingraham Peck's ad- 

 mirable paper on "The Sources of Marine Food."* 



The littoral benthos in general differs from oceanic ben- 

 thos : ( 1 ) in that bodily structure is not specialized to 

 withstand great pressure; (2) as the littoral sea bottom is 

 comparatively well lighted by the rays of the sun, there is 

 not such a tendency to phosphorescence as in deep sea life; 

 (3) the great diversity of littoral life is in harmony with 

 the varying character of its substratum; (4) the coastal 

 area is much more crowded than the oceanic floor on ac- 

 count of its shallowness, its more limited extent, its rich 

 food supply, and its great diversity of life. 



Other important ecological factors are the rise and fall 

 of the tide, laying bare entire animal associations twice a 

 day, the effect of the waves and coastal currents on exposed 

 shores, and of the brackish waters near river mouths. 



On muddy bottoms, we find animals adapted to burrow 

 either for protection or food, especially worms and mol- 

 lusks, as is the case also in more sandy tracts, with a some- 

 what different range of species, while in rocky crevices and 

 tide-pools animals like hydroids, sea anemones and sponges 

 abound, anchored safely by holdfasts and clinging organs, 

 while echinoderms and Crustacea lurk in crevices. The 

 various seaweeds peculiar to such situations, and the 

 hydroids as well, shelter hosts of small forms — worms, 

 nudibranchs, snails, pycnogonids, amphipods. Every niche, 

 every possible locality, is occupied, wherever indeed a liveli- 

 hood may be gained, and its possession is fought for. 

 Crawling, running, and swimming everywhere are the scav- 



* Bulletin United States Fish Commission for 1895, pp. 351-362. 



