30 PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



and Goniastrea. The Porites and Pocillopora reach their maxima at 1,400 

 to 1,450 feet from shore, and Goniastrea pectinata and retijormis are the 

 dominant corals of the crevice-like tide-pools of the lithothamnion ridge. 



The mode of distribution and frequency of occurrence of the various 

 species of corals over the southeast reef are shown diagrammatically in 

 figures 6 to 8, and the significant fact is that, with the exception of Seriatopora 

 hystrix, all the other species are reduced in numbers near the middle of the 

 reef-flat at about 1,100 feet from shore. This, indeed, is the region in which 

 Seriatopora hystrix attains its acme and covers about 40 per cent of the area 

 of the reef and constitutes 70 per cent of the coral heads, thus crowding out 

 the other species. It is a clear illustration of the struggle for existence 

 between the various species of corals. 



About one-half of the species of the reef-flat are confined to the outer 

 zone between 1,000 feet from shore and the seaward edge of the reef, while 

 of the abundant forms only two, Porites andrewsi Vaughan and Cceloseris 

 mayeri Vaughan are shore corals, being practically confined to within 1,100 

 feet of the beach. 



No corals were found growing in situ within 440 feet of the shore, the 

 three coral heads found on the square 375 to 425 feet from shore having been 

 driven shoreward on loose blocks of limestone in time of storm. 



In general, it appears that each of the common corals attains a well- 

 defined maximum at some definite distance from shore and declines in 

 frequency both shoreward and seaward of this most favorable locality. In 

 order to find the reason for this one must determine the physical factors of 

 the environment at different places over the reef-flat and with this in view 

 a series of temperatures were taken at various states of the tide and times 

 of the'day. 



