242 MARINE ANIMALS 



denser populations, is not known. Deep bays, fiords, lagoons of coral 

 reefs, etc., operate like traps, in which large numbers of macro- 

 plankton, such as salpas and medusae, accumulate at certain seasons. 

 In the spring of 1900, velellas, physalias, and ianthinas had been 

 driven into the Bay of Naples in such numbers that they covered 

 millions of square meters; all were stranded and destroyed by the 

 beginning of May. 29 Both oceanic and neritic plankton suffer in storms, 

 and are driven ashore in great masses. Windrows of dead velellas more 

 than half a meter high and a kilometer in length appear on the coast 

 of the Riviera after storms; in August 1883, the beach at Kristineberg, 

 Sweden, was covered with a thick glowing mass of the protozoan 

 Noctiluca; 30 and in September 1893 the water at that place was a 

 thick greenish broth of the holopelagic copepod Anomalocera patersoni. 



Oceanic and neritic areas are contrasted as poor and rich in the 

 density of their populations, the difference between them being greater 

 than that between the polar and tropical Atlantic. 31 The reason lies 

 in the better food supply of the shallow water. The plant detritus due 

 to the neighborhood of the coast, and the richer fertilization of the 

 water in the vicinity of land (cf. p. 170) , make possible a greater devel- 

 opment of the plant plankton. Plankton bacteria are much less abun- 

 ant in the open ocean than near land. The increase in the animal 

 population follows directly. It is the richer food supply which keeps 

 various holopelagic animals, which have been able to adapt themselves 

 to the change, in the neritic area. The number of appendiculates in a 

 tenth of a cubic meter of water may reach 600 in shallow water, while 

 it sinks to 13 in the -water of the open ocean. 32 



The population of the pelagial is a well-characterized association 

 almost entirely self-sustaining, and hence rather sharply distinguished 

 from neighboring associations. The food chain here represented extends 

 from the small single-celled algae to the larger fish and toothed 

 whales, as already shown. The dependence of various elements of the 

 food chain on a preceding one conditions the distribution of the larger 

 forms. The mackerel fishery at the mouth of the English Channel 

 depends on the amount of animal plankton, especially copepods ; corre- 

 sponding to variations in the plankton, it was good in 1905, poor in 

 1906, and good again in 1907. 33 The appearance of the herring on the 

 north coast of Iceland is dependent on the summer development of 

 the copepod Calanus. The complicated migrations of the herring, with 

 the exception of their breeding movements, are probably due to varying 

 food supply. The distribution of whales 34 is also dominated by their 

 food supply. The baleen whales are at home in the arctic and antarctic 

 seas, where such an excess of plankton develops at certain seasons. The 



