Nos. 620-621] THE HAWAIIAN CORAL REEFS 



411 



ful vividness. Mauna Loa, the greatest active volcano 

 on the planet, dominates the island of Hawaii. Its colos- 

 sal dome is crowned by a summit lake of reverberating 

 liquid lava, with spectacular displays of high-jetting fire 

 fountains. The bulk of the island is still growing, 

 through intermittent outpourings of lava. Ocean Island, 

 on the other hand, is the last white fragment of a subsid- 

 ing coral-crowned mountain— perhaps a dead volcano, 

 that may have resembled Loa in many respects, but which 

 has been drawn inexorably into the abysses of the Pacific. 

 One represents the culmination of the volcanic forces; 

 the other the climax of coral work— an atoll on a tropic 



Of the larger eastward islands, Kauai and Oahu are of 

 particular interest, as they have the largest coral reefs, 

 and support the most luxuriant marine life. The reefs 

 are all of the fringing or platform type, and vary in width 

 from a few hundred feet to half a mile. Reefs are well 

 developed along the southern or leeward shores of the two 

 Islands mentioned, and also, to a lesser degree, along the 

 northern coasts. Oahu is almost encircled by coral reefs, 

 whereas Kauai, Molokai, and Maui have numerous coastal 

 stretches wholly free from coral. The little island of 

 Niihau, to the west of Kauai, has considerable coral reef. 



It is significant to note that although the majority of 

 corals, particularly the more massive reef-building forms, 

 occur only in the shallow waters of tropic seas, there are 

 a number of species that inhabit deep, cold waters. 

 Lophohelia prolifera and Dendrophi/lUa ramea, for ex- 

 ample, form dense beds at depths of from 600 to 1,200 

 ft. off the coasts of Norway, Scotland, and Portugal. 

 The general requirement, however, is shallow water whose 

 mean temperature does not fall below 68° F., and the 

 reef-building species do not flourish unless the tempera- 

 ture is considerably higher. Although a single Hawaiian 

 species of mushroom-like coral (Bathyactes Haivaii&nsis) 

 was dredged by the Albatross from a depth of nearly 

 7,000 ft., most of the Hawaiian forms live in waters of 



