Handbook of Paleontology 101 



of seaweed. Rock pools even are affected unless they 

 are deep and shaded. Daily variations in temperature 

 are more noticeable in more northern waters than in 

 the tropics, but the seasonal variations are most im- 

 portant, particularly along coasts where the climate 

 is so cold that the water freezes and the life of the 

 tidal area is exposed to prolonged frosts during the 

 many hours each day that it is uncovered. We have 

 here not only the injurious results of the frosts, but 

 the even more destructive effects resulting from move- 

 ments of ice due to tides and tidal currents or storm 

 waves. Rocks, large stones and boulders get quite 

 thoroughly scraped. At Wood's Hole, Mass., where 

 parts of the coast are at times almost entirely frozen 

 over, the rocks have been found to be scraped almost 

 entirely bare of algae by the time the ice disappears 

 in the spring. As we should expect, therefore, Arctic 

 and Antarctic shores have no invertebrate animals. 

 Great damage is often done to mussel beds through 

 intense frosts, especially high up where they are ex- 

 posed by the retreating tides. Such an occurrence is 

 recorded from the Lancashire coast, England, where, 

 during a spell of cold one winter, the whole coast was 

 covered with ice-floes for a long time and the cockles 

 were killed in large numbers. The first storm follow- 

 ing the frost washed up dead cockles by the hundreds 

 of tons. Certain animals avoid the severe effects of 

 seasonal changes of temperature through seasonal mi- 

 grations. Crustaceans, such as the lobsters and crabs, 

 migrate to the deeper waters in the cold season. The 

 decomposing beds of seaweeds along the shore that 

 serve as a refuge to creatures needing moisture in the 

 summer, serve also as a warm shelter during periods 



