ECOLOGY OF THE MURRAY ISLAND CORAL REEF. 15 



To Davis should be given the credit for having called renewed and prominent 

 attention to the importance of making a careful study of shore-line topog- 

 raphy in relation to the coral-reef problem. 



To return to the consideration of Maer Island, the "lithothamnion 

 ridge" extends only from the middle of the southeast side to near the 

 northern corner of the island, this being the region subject to the sweep of 

 the breakers due to the southeast trade wind. 



On the northwest, south, and southwest sides there is no "lithothamnion 

 ridge," for breakers rarely occur in these regions; moreover, the growth of 

 the lithothamnion ridge is prevented along the southernmost half of the 

 southeast side by the silt from Haddon and Hedley brooks; while Bruce 

 Brook produces the same effect at the northern end of the island. 



The structure of this so-called "lithothamnion ridge" is interesting. It 

 consists of a nearly flat plateau elevated about 6 to 8 inches above low-tide 

 level and usually about 150 feet wide at low spring tide. There are many 

 shallow tide-pools over this ridge, but these are rarely more than a foot wide 

 and 3 to 5 inches deep. 



Numerous corals grow in these tide-pools, 201 living coral heads being 

 counted within a 50-foot square at the crest of the lithothamnion ridge. 

 These corals present a remarkable appearance; the branched Acropora and 

 Pocillopora bulbosa are stouter-stemmed and more compact and rigid than 

 are stocks of the same species which grow in the protected waters of the reef- 

 flat a few hundred feet nearer shore. (See plate 12, figs. 1-3.) Moreover, 

 the surviving stems of the branching corals nearly all bend inward toward 

 the shore, reminding one of the gnarled and twisted trees one sees upon a 

 wind-swept beach. There are many massive coral heads, such as Goniastrea 

 pectinata, living within the cleft-like pools of the lithothamnion ridge, but 

 most of them are hardly more than mere incrustations clinging to almost 

 every crevice in the rocky floor of the shallow tide-pools over which the break- 

 ers dash in full force. As is well known, the effects of environment upon the 

 growth-forms of corals have been especially discussed by von Marenzeller, 

 1906, in his work on Red Sea corals, by Pace, who observed Turbinaria in 

 Torres Straits, and also by Wood Jones and by J. Stanley Gardiner, in their 

 studies of Cocos Keeling and of the Maldive Archipelago, respectively; 

 and by Vaughan in several publications. Especially interesting is the account 

 which Wood Jones gives in his "Coral and Atolls," 1912, pp. 69-134. 



All corals in the tide-pools of the lithothamnion ridge are cut off squarely 

 at the low-tide level of the water contained in the tide-pool and thus they are 

 usually not more than 2 to 5 inches high, although in the larger pools they 

 may be a foot or more in width. 



All dead parts of these corals are incrusted with a growth of Lithotham- 

 nion, Bryozoa, and nullipore algjc, which also form a general veneer over the 

 rocky crest of the ridge. Thus, upon a superficial inspection the ridge 



