THE GENERAL CHARACTERISTICS OF SHORE ANIMALS. 3 



ence is primary when, as in many pelagic worms, molluscs, 

 artd sea-squirts, the minute plants are actually taken as 

 food ; it is secondary when, as in many fish, the food 

 consists of the worms, molluscs, sea-squirts, etc., which 

 themselves feed upon the Algse. Abundantly supplied with 

 air and sunlight, the little plants grow and multiply rapidly, 

 and constitute the great basal food-supply of the animals of 

 the open sea. 



Many of those minute plants, or plant-like animals, occur 

 also in the shallow shore waters, and there again constitute 

 an important part of the food-supply, but this is supple- 

 mented in two ways. First, we have an enormous amount 

 of material carried into the sea by rivers. It is a fact of 

 common experience that mudbanks of varying size usually 

 occur about the mouths of rivers. The constituent mud is 

 brought clown by the river, and it contains an abundant 

 supply of nutrient material, of which very many shore 

 animals avail themselves. Second, we have the large fixed 

 seaweeds, which can flourish only in water shallow enough 

 for the light to reach them, and which occur in great variety 

 and abundance around our shores wherever there are rocky 

 surfaces to which they can affix themselves. 



According to their diet we may divide the shore animals 

 into three sets: (1) those which are vegetarian in habit, 

 living upon the large seaweeds ; (2) those which feed upon 

 minute food-particles contained in the water or in sand and 

 mud ; (3) those which are carnivorous and depend upon 

 the two preceding sets for food. All these three sets find 

 food most abundant in the vicinity of rocks. The first 

 obviously do so because the large seaweeds grow well only 

 when fixed to a solid base. It may not be quite so clear 

 why the statement is true of the second set, but it is a fact 

 that shore animals which feed on microscopic particles are 

 sedentary animals, not capable of resisting by their own 

 activity the force of shore currents and shore waves. In 

 consequence they usually cannot flourish unless, like the 

 shore weeds, they have a firm basis of attachment. The 

 chief exception arises in the case of burrowers which often 

 live in sand quite away from rocks. As the carnivorous 

 animals depend upon the preceding two sets, it is obvious 

 that they can abound only in the vicinity of the rocks 



