320 LIFE BY THE SEASHORE. 



within a reasonable distance from the shore is very much 

 less than 100 fathoms, and usually not more than thirty to 

 fifty fathoms, so that in most places we may say that our 

 littoral fauna includes the animals found on the bottom 

 in all depths from 0-30 fathoms. Even this is a con- 

 siderable range of depth, and it is natural to ask whether 

 it is not possible to divide the littoral area into zones ac- 

 cording to the depth. Such attempts have frequently 

 been made, but we have already emphasised the fact that 

 depth is only one of the factors determining distribution, 

 and perhaps not the most important factor. Other factors 

 are wave-action, temperature, food, the salinity and clear- 

 ness of the water, the nature of the bottom, and so on. 

 We shall therefore consider certain areas of the littoral 

 region as determined by the nature of the bottom rather 

 than by depth alone. Thus the bottom may be rocky, a 

 condition often well exemplified between tide-marks, where 

 the ebb and flow of the tide and the action of the at- 

 mosphere split and fissure the rock surfaces, hollowing 

 them out in a way which renders them eminently suitable 

 as haunts for many animals. The rock surfaces are over- 

 grown with luxuriant weeds, green, brown, and red. 

 Near low-tide mark one sees the great blades of oar-weed 

 (Laminaria) marking the shoreward limit of the Lamin- 

 arian zone, which extends downward to a depth of fifteen 

 fathoms. On rocky coasts one finds that the dominant 

 forms from high-tide mark to the margin of the Lamin- 

 arian zone are limpets, periwinkles, tops, dog-whelks, the 

 shore crab, many Amphipods and other small Crustacea, the 

 hardy smooth anemones, acorn-shells, the common starfish, 

 and other hardy forms. In the Laminarian zone itself an 

 enormous number of interesting and beautiful creatures 

 occur sea-urchins, starfish, brittle-stars, many anemones, 

 the delicately tinted sea-slugs, spider-crabs, the edible crab, 

 prawns and Mysids, Galathea and porcelain -crabs, many 

 Annelids, and so on. Again, if the bottom be of sand or 

 mud, instead of rocks, the great oar-weeds are replaced by 

 sea-meadows of Zostera, among whose grassy blades the 

 sea-hare, the cuttles, and many other interesting Molluscs 

 lurk. By digging in the sand or mud one gets all those 

 interesting creatures we have already mentioned burrow- 



