THE TEMPERATURE OF THE FLORIDA CORAL-REEF TRACT. 



INTRODUCTION. 



The temperature data herewith presented were assembled prhnarily for 

 their bearing on the effect temperature exerts on the bathymetric and geo- 

 graphic distribution of coral reefs. The following quotation from an article 

 I have recently published will, I believe, immediately indicate the bearing. 

 In discussing the factors which may determine the lower bathymetric limit 

 of shoal-water corals, it is said •} 



"Another factor is temperature. Dr. Mayer conducted a series of experiments 

 to ascertain the higher and lower limits of temperature which the common corals 

 around the Tortugas can endure. These indicate that a lowering of the tempera- 

 ture to 13.9° C. would exterminate the principal Florida reef corals, while the most 

 important inner flat corals would survive. He obtained similar results on the 

 corals around Murray Island, Austraha. 



"Dr. H. F. Moore of the U. S. Bureau of Fisheries has communicated to me 

 temperature records made at lighthouses along the Florida reef. These show 

 that vigorous reefs will endure a temperature as low as 18.15° C., the mmimum 

 at Carysfort light between 1879 and 1899; but at Fowey Rocks, where the minimum 

 drops to 15.6° C, although there are some corals, there is no thriving reef. The 

 species found at the north end of the reef line are those which Dr. Mayer's experi- 

 ments showed capable of withstanding the lowest temperature. The temperature 

 records for the reef line indicate 18.15° C. as the minimum temperature which a 

 reef will survive — this is 1.85° C. lower than the figure given by Dana. It is not 

 probable that a reef could withstand a continuous temperature so low as this. 

 Wherever the depth of water is great enough to lower the bottom temperature 

 below 18.15° C, more probably about 21° C, reef corals will not live. This 

 temperature appears to be attained around the Hawaiian Islands within a depth 

 of 183 meters. According to Agassiz's 'Three Cruises of the Blake' the bottom 

 temperature in the Gulf of Mexico and the Caribbean Sea is usually too low for 

 the growth of reef corals at a depth of 183 meters, and in places it is too low at a 

 depth of 87 meters. Although the possibility of control of the lower bathymetric 

 limit of reef-building corals by decrease in temperature with increasing depth has 

 not been adequately investigated, it appears safe to say that reef corals are usually, 

 if not always, confined by temperature to water less than 180 meters deep." 



The table of salinity and temperature near Bermuda, the Bahamas, 

 and Florida, pages 337, 339, shows that the temperature at 300 meters is 

 uniformly too low for the life of reef corals; it is usually too low at 200 

 meters; and occasionally too low at 100 meters, in an area where the surface 

 temperature is high enough for the life of reef-forming corals. 



Temperature, of course, is not merely a factor in determining bathymet- 

 ric distribution; it is also one of the most impotrant factors in determining the 

 geographic distribution of sea-level and near sea-level reefs. The importance 

 of this relation is made sufficiently clear in the foregoing quotation. 



Dr. Mayer, on page 34 of his paper on the ecology of the Murray Island 

 reef, presents the results of his experiments on the limits of artificial heating 



'Nat. Acad. Sci. Proc, vol. 2, pp. 97-98, 1916. 



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