ZONES OF THE SEA-WHERE THEY LIVE 21 



uncover this zone, great changes in wetness, temperature, salinity, light, 

 and friction produced by the harsh buffeting of waves are experienced. On top 

 of all this, food is rather scarce, being present for most animals only when 

 water covers them. This means that the animals and plants of this zone have 

 to be the hardiest in the sea. It also means that from the low-water mark to 

 the high-water mark, conditions become harsher and harsher and more and more 

 like conditions on land, and that life becomes more and more impoverished. 

 Therefore, it is not surprising to find that many eulittoral animals and plants, 

 such as periwinkle snails, blennies, and gobies, show tendencies toward 

 terrestrialism. 



This zone is subdivided according to the nature of the bottom into rocky, 

 sandy, and muddy shores. Rocky shores are characteristic of eroding coast lines. 

 This solid substratum forms an anchorage for sessile forms of life such as rock- 

 weed (Fmcms), barnacles, mussels, snails of various sorts. Here life piles on life. 

 As soon as one animal or plant anchors itself to the rock, another may anchor 

 next to it or attach itself to the original resident. Great numbers of small 

 animals live almost exclusively attached to seaweeds or shells. Most of the ani- 

 mals either bore into rock for protection or have heavy shells themselves. The 

 plants are tough and resilient so as to be able to vvithstand the beating of 

 the waves. 



Tidepools are little rock communities in themselves. A great variety of life 

 that can stand wide ranges in salinity, high temperature, and quiet water lives 

 here, including small fishes such as gobies and killifish, bryozoans, hydroids, 

 seaweeds, tunicates, worms, sponges, anemones, barnacles, and mussels. 



Sandy and muddy tidal shores are typical of depositing coasts. Marsh grasses 

 such as Spartina are invaders from the land and are not bona fide marine plants. 

 The invertebrate fauna is dominated by burrowing forms such as clams, whelks, 

 sand bugs CJ^ippa), and worms. In places where there are no aquatic plants 

 but where marsh grass is found, a great variety of snails, crustaceans, starfishes, 

 crabs, and others are added. Soft bottoms of a mixture of sand and mud are richer 

 than either sand or mud alone. This illustrates the general principle that mix- 

 tures of habitats usually produce richer fauna than either habitat does when 

 pure. 



THE SUBLITTORAL OR SUBTIDAL SUBZONE 



The types of animals and plants of the tidal zone are also usually typical of 

 the nontidal zone, except that the species are richer and more varied here. Once 

 again, there is a division into rocky, sandy, and muddy shores. 



The rocky shores bear extremely rich faunas which have at their base great 

 forests of plants or plantlike animals, such as kelp or corals. As in the tidal 

 zone, life builds on life, but fishes are dominant. Animals here usually have 

 heavy protective shells (abalone), spines (sea urchin), or protective coloration 

 (octopus). Every phylum of the animal kingdom is represented, with the 

 notable exception of the exclusively pelagic arrow worms. 



The loose substrata of sand and mud are like those of the tidal zone except 

 that they are richer, containing flatfishes, rays, stargazers, anglers, squids, 

 prochordates such as Amfhioxus, and a greater variety of crustaceans, worms 



