168 FOUNDERS OF OCEANOGRAPHY 



deep-sea forms, and comparatively few species have a wide 

 bathymetrical range. 



2. Temperature has a profound effect upon the distribution 

 of most marine organisms. As notable examples on a large 

 scale may be given the distribution of coral reefs, which are 

 only found in tropical seas, where the temperature through- 

 out the year is not lower than 68° F. ; and the case of sea- 

 fisheries, many of which are determined by the temperature 

 of the water in which the fishes Uve. Rise of temperature 

 increases the rate of metabolism in an organism, and this 

 probably has far-reaching effects in the sea. Then, again, 

 the secretion of carbonate of lime by marine animals is greatly 

 increased by a rise of temperature. 



3. Salinity, etc. Some animals can only exist in water of 

 a certain density, some only deposit their eggs under certain 

 conditions of saUnity, and the flotation and further develop- 

 ment of the eggs and later stages of many of our food-fishes 

 depends upon the specific gravity of the water. Moore, 

 Roaf, and others, in their work at the Port Erin Biological 

 Station, have shown that the chemical characteristics (hydro- 

 gen-ion concentration or alkalinity) of the sea have a pro- 

 found effect upon the development of embryos and larvse. 

 The shoaling movements of the herring, which give rise to 

 important fisheries, take place successively farther and 

 farther south on the east coast of Britain during summer 

 and autumn, and this is associated with the sahnity of the 

 sea, as Atlantic water of 35°/oo and temperature 13° to 15° C. 

 moves south from the Shetlands towards the English 

 Channel. The winter herring of the Skager-Rack do not 

 frequent Atlantic water, but are found in the " Bank " water 

 of 32o/oo to 33°/oo. Consequently, when there is too much 

 Atlantic water entering the Skager-Rack, no winter herring 

 fishery takes place. 



4. Pressure is obviously an important factor in the Hfe of 

 deep-sea animals, and probably in varjdng degree determines 

 the distribution of many others at lesser depths. 



