ECOLOGY OF THE MURRAY ISLAND CORAL REEF. 



23 



- 



Fig. 5.- 



50 Feet 

 -A 50-foot square laid out 

 in crossbars. 



In order to determine the conditions of association and abundance of 

 the various species of corals which grow upon the southeast reef-flat, squares 

 50 feet on the side were surveyed and their boundaries were marked by ropes 

 secured by iron rods driven into the rocky floor of the reef-flat. Each of 

 these squares was still further marked off by lines stretched from one side 

 to that opposite, thus forming a "gridiron" pattern, 50 feet wide on each of 

 the sides and with from 3 to 5 feet between the "crossbars." It was then a 

 simple matter to count 

 all coral heads in each 

 alley-way between the 

 cross-bars, and as each 

 headwascounted it was 

 scarred by being struck 

 with a crowbar, thus 

 avoiding the probabil- 

 ity of any head being 

 counted twice. 



The water being of 

 crystalline clarity and 

 the surface beingusually 

 but slightly rippled, no 

 serious difficulty was ex- 

 perienced in counting 

 and identifying the cor- 

 als, although in some 

 genera the more closely 

 related species could 

 not be distinguished one 

 from another, and are 

 thus grouped under the 

 most probable specific 

 name. This applies es- 

 pecially to Acropora, 

 Pontes, and Favia. The 

 number of living heads 

 on the 50-foot squares 

 increases from 2 on the square 375 to 425 feet from shore to 1,838 on the 

 square 1,400 to 1,450 feet from shore, this being about 200 feet shoreward 

 from the inner wash of the breakers. 



Beyond this, toward the outer edge of the reef, the number of coral heads 

 decreases, being broken in time of storm, but the species increase in number, 

 becoming most numerous in the region of the inner surge of the breakers; 

 even on the crest of the Lithothamnion ridge, which is laid bare for fully an 

 hour at spring tides, there were 201 living coral heads on a 50-foot square. 



i<« 00 



1600 



1750 



IN FEET FROM SHORE 



Fig. 6, 



600 800 



DISTANCE 



-Illustrating table 3, showing the number of coral heads at each station 

 on Line No. I across the southeast reef-flat of Maer Island. 



