ECOLOGY OF THE MURRAY ISLAND CORAL REEF. 



17 



Thus the reef extends seaward at a rate dependent upon the average 

 growth-rate of densely clustered coral heads and if this be taken at one-half 

 inch per annum the wide southeast reef-flat of Maer Island might have been 

 formed in 28,800 years, although one must not take such an estimate at all 

 seriously, for many factors may enter into the case which we have not 

 evaluated. 



Considering Maer Island as a whole, it appears that where the reef is 

 fully exposed to the breakers of the southeast trade-wind and is fairly free 

 from silt it grows rapidly seaward. In silted regions and in quiet water, 

 however, the reef does not grow so rapidly. For their best development 

 corals require pure, moderately agitated water; only a few forms, such as 

 Porites andrewsi Vaughan and Cceloseris mayeri Vaughan, thrive best in semi- 

 stagnant regions where the bottom is muddy. The most luxuriant growth 

 of corals on the southeast reef is found about 200 feet inward from the inner- 

 most wash of the breakers, at 1,400 feet from shore. Seaward from this 

 region the corals thrive well, but are apt in time of storm to become broken 

 by the surges. 



ANNUAL GROWTH OF CORALS. 



As the coral reefs of the Murray and other islands of Torres Straits 

 have apparently grown seaward over their own outer slopes during the recent 

 period of quiescence, it becomes important to 

 know something respecting the rate of growth 

 of reef corals in this region. Fortunately, for 

 this purpose certain corals lying off Vivien 

 Point, Thursday Island, were measured and 

 photographed by Saville-Kent in June 1890. 

 On November 4 to 10, 1913, some of these 

 corals were identified by the present writer 

 with certainty; while others had evidently 

 disappeared or died, or could not be recog- 

 nized from Saville-Kent's description. Thus, 

 the large Goniastrea in the foreground of 

 Saville-Kent's Plate II of his "Great Barrier 

 Reef of Australia" has disappeared, and we 

 were told that a number of coral heads were 

 gathered from this region about ten years ago 

 and used for making a retaining wall for the 

 road along the shore. The Symphyllia, which 

 occupies a prominent position on the extreme 

 right in the plate just referred to, on November 8, 1913, was 74 inches in its 

 longest diameter, N. 15 W. to S. 15° E., and 65 inches in the diameter transr 

 verse (90 ) from the longest. The upper surface of this coral is now largely 

 killed, the dead area being 53.25 inches by 43.75 inches with an isolated 



I 



N.I5°W. 

 SHORE 

 Fic. 4. — Saville-Kent's Symphyllia seen from 

 above on November 9, 1913. The dotted 

 parts are exposed at low tide and are dead. 

 There were no dead areas upon this coral- 

 head in 1890 and it was then regular and 

 dome-shaped; now it is flat and mainly dead 

 above, but growing laterally. 



