CORAL REEFS OF TORRES STRAITS 



219 



upon the southeast reef-flat are distributed, and in order to gather a 

 census of the corals, a line was surveyed across the reef, and at intervals 

 of 200 feet, squares of 50 feet on the side were staked off and all the 

 coral heads on each square were counted. 



The shallows within 350 feet of the shore" lack corals, the bottom 

 being covered with a thin layer of limestone mud which supports a 

 vigorous growth of a short-bladed eel grass, Posldonia australis. 



On the square whose center was 400 feet from shore, only three small 

 coral heads were found, and these were growing upon loose corroded 

 limestone blocks which had been washed shoreward from the outer parts 

 of the reef-flat. As one goes outward, however, the coral heads steadily 

 increase in number becoming a maximum at 1,425 feet from shore where 

 there were 1,838 coral heads on the square. Even the crest of the 

 lithothamnion ridge 1,750 feet from shore had 201 living coral heads 

 clinging to the bottom of its shallow tide pools, although the ridge itself 

 was here fully six inches above the level of the lowest tides. 



There must be some cause for this tendency on the part of the corals 

 to grow best at considerable distances from shore. The truth of the 

 matter is that corals are very sensitive to changes of temperature and 

 an ocean as cold as 56° or as warm as 98° F. would be fatal to all the 

 reef-building forms. The more delicate corals such as the finely- 

 branching Seriatopora or the "stag horns," formerly known as Madre- 



Pout Moresby, Papua, showing the drowned character of the coast. 



