78 THE BIOLOGY OF THE SEA-SHORE 



we are not concerned here, but for the way in which they 

 illustrate the problem of varying temperature, a problem 

 which is evidently presented in its acutest form in the 

 shallow waters of the tidal zone. 



The effect of extremes of temperature has been to give 

 rise to many interesting adaptations to seasonal changes. 

 These, as might be expected, are mostly concerned with 

 reproduction and are fully discussed under that heading. 

 Extremes of heat and cold tend to produce a similar result ; 

 for instance, in the Mediterranean, the shallow and stagnant 

 waters of harbours, and the like, which are subject to intense 

 putrefaction and excessive heating in summer, are populated 

 by species which mostly reproduce in winter and spring 

 (Lo Bianco, 191 1). Such conditions are probably rare 

 around the coasts of Britain, where cold is a more important 

 factor. Prolonged frosts have been shown to have a material 

 effect on mussel beds, particularly those higher up the 

 shore, which are uncovered for many hours a day. 

 Similarly an intense frost may kill large numbers of cockles. 

 In the winter of 1904-5, when the whole of the Lancashire 

 coast-line was covered with ice-floes for a considerable time, 

 many hundreds of tons of dead cockles were washed up by 

 the first gale after the frost had disappeared (Scott, 1909). 

 Unfortunately there are very few data dealing with the effects 

 of temperature on the occurrence of shore animals, at least 

 round British coasts, and a detailed study of a particular 

 piece of shore at all seasons should be very instructive. 



Where the cold is so intense as to cause the water to 

 freeze, the effect on the shore fauna and flora is particularly 

 deleterious. At Woods Hole, where sheltered portions of 

 the coast are at times during the winter more or less com- 

 pletely frozen over, the movements of ice along the shore 

 and through channels, whether due to the rise and fall of 

 the tide, to storms, or to tidal currents, serve to scrape bare 

 the large stones and boulders so that they are frequently 

 almost or entirely bare of algas when the ice disappears in 

 the spring. The same is sometimes true of the common 

 barnacle {B. halanoides) which covers these surfaces in 



