American Fisheries Society 211 



animals of the benthos may be either predatory in habit, 

 feeding upon each other, or they may l)e scavengers, but 

 ultimately their food supply is either directly or indirectly 

 derived from the plankton of the ocean al)ove them, the 

 countless individuals of which, momentarily dying, con- 

 tinually rain down their tiny mote-like corpses tcj the ocean 

 floor, where they are immediately devoured by sessile ani- 

 mals, such as actinians, hydroids, pelecypod mollusks and 

 tube-building worms, while many of these in turn become 

 the food of lx)ttom-fishes, crabs, snails, echinoderms, and 

 other predaceous creatures. Since, however, much of this 

 planktonic shower is consumed in transit and reaches the 

 bottom much diminished in volume, the benthos of the 

 deeper ocean must likewise be limited in abundance as com- 

 pared with that of the shore. 



2. LITTORAL ECOLOGY 



The ecological conditions of the marine fauna <»f our 

 shores stand in sharp contrast to those of the oceanic 

 waters, on account of their far more complicated character. 

 In the open sea, conditions of temperature, depth, currents, 

 etc., are comparatively uniform, and are spread over vast 

 areas, while changes are relatively gradual. 



As we approach the shore, and arrive at the limits of 

 the continental shelf, the sea bottom rapidly rises from a 

 depth averaging two miles or more to that (jf about 100 

 fathoms. At the same time we come within the influence 

 of the variable local currents, while the action of the tides 

 and the influence of the waves become more marked. Other 

 important factors, with a direct bearing on the character 

 of the littoral fauna, are the reduced pressure of the shal- 

 lower areas and the penetration of the sun's rays to the 

 ocean floor. The waters of the ocean also become greatly 

 modified in the neighborhood of river mouths, where their 

 salinity and density are diminished by the volumes of fresh 

 water continually poured forth. The temperature of the 

 water too is more variable, as it ranges between greater 

 extremes of heat and cold during the year, and is more sub- 



