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PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



EXPERIMENTS UPON THE EFFECTS OF SILT ON CORALS. 

 The fact that corals which are sensitive to high temperature do not 

 occur within 500 feet of the shore, while those which can survive the heat do 

 occur in this region, suggests that temperature is the controlling factor, 

 although there may he others which operate in conjunction with or inde- 

 pendent of temj)erature and which would themselves suffice to prevent the 

 growth of corals in this region. For example, in time of rain or during 

 storms a considerable quantity of silt becomes stirred up from the bottom 

 and mud is also poured out over the reef-flat from the steep slopes of the 

 island, and this may be a determining factor in checking the growth of corals 

 within 500 feet of the shore. Accordingly, tests were made aiming to deter- 

 mine the ability of the various common reef-flat corals to resist silt, the corals 

 being buried about 2 inches under the fine limestone mud covering the floor 

 of the reef-flat. The results are stated in table 9. 



Table 9. — Experiments upon burying:, corals 2 inches under the mud of the reef-flat, the water 

 over the mud being 6 inches deep at lozv tide. 



It appears that the corals which are confined to the seaward parts of 

 the reef-flat beyond 500 feet from shore are those which can not withstand 

 being covered with mud for 14I hours, whereas the dominant inshore corals 

 can still survive after being buried for 24 hours beneath the mud. Thus, 

 Seriatopora hystrix, Pocillopora bitlbosa, Acropora hebes, and A. palifera are 

 very sensitive to the smothering elTects of silt and these are all off-shore forms. 



On the other hand. Pontes andrewsi Vaughan, P. mayeri Vaughan, Coelo- 

 seris mayeri Vaughan, and Goniastrea pectinata, which are the dominant forms 

 close to the shore, can usually withstand being covered with mud for 24 hours. 



We may therefore assert that the off-shore corals, those which can not 

 live within 500 feet of the beach, are forms which are sensitive both to high 



