28 PAPERS PROM THE DEPARTMENT OF MARINE BIOLOGY. 



heads per unit area, as one goes inward from the 1,400-foot station toward 

 shore, is due to a corresponding decline in the food supply, the more favored 

 corals' on the outer parts of the reef-flat devouring most of the pelagic and 

 other food-animals. But in his study of the Florida corals in 191 2 Vaughan 

 pointed out the fact that the fleshy parts of well-fed corals appear plump and 

 distended, while those of starving corals are drawn and thinly spread over 

 the skeleton; and judging by this criterion, it seems that the corals near 

 shore are quite as well supplied with food as are those farther out on the 

 reef-flat. This leads one to suspect that the food supply is everywhere more 

 than sufficient for the corals, but the case should be tested by making obser- 

 vations upon the growth-rate of corals near shore and far out upon the reef- 

 flat, and also quantitative studies should be made of the plankton at various 

 states of the tide and at different distances from shore. Unfortunately, 

 these studies were not attempted at Murray Island, the duration of our stay 

 there being too short to render the results of such an investigation reliable. 

 Considering the zone of reef-flat which is 1,150 feet wide and lies between 

 500 and 1,650 feet from shore, there are on an average 785 living corals on 

 each 2,500 square feet, and thus upon the 2 miles of reef-flat there are 

 probably 3,600,000 coral heads. 



Despite the large quantity of zooplankton required to provide these 

 corals with food, it seems that conditions other than the supply of nourish- 

 ment are probably responsible for their decline in number as we go inward 

 from the 1,400-foot station toward the shore. 



It will be recalled that Gardiner was of the opinion that corals might be 

 nourished in some measure by their commensal plant cells, and certainly, as 

 Vaughan has observed, reef corals do not thrive in shaded places, under 

 docks, etc., although only a few feet distant, where sun-light is able to pene- 

 trate, they may flourish in abundance. In order to test this matter, Vaughan 1 

 placed 18 species, representing practically all the important reef corals of 

 Florida, in a submarine dark chamber for 43 days. At the end of this time 

 most of the corals were decidedly bleached, owing to the death of their plant- 

 cells, but in only 5 species did the corals themselves die. This would lead 

 one to suppose that the plant-cells are not so essential to the life of the reef 

 corals as has often been supposed. Certainly they do not directly supply 

 nourishment, for corals refuse all plants as food. Corals, however, are not 

 the only coelenterates which are independent of their commensal plant-cells 

 for food, for the scyphomedusa Cassiopea, if kept in the dark for more than 

 a month, loses most of its infesting zooxanthella: and yet lives apparently as 

 well as ever, and Whitney demonstrated that Hydra if deprived of its green 

 algal cells lived quite as well as if they were present. 



The coral reefs of the Murray Islands are among the richest of the entire 

 Barrier Reef. Being 70 miles from the New Guinea coast, they are removed 



'Vaughan, T. W„ 1914, Carnegie Inst. Wash. Year Book No. 13, p. 225. 



