ZOOLOGY: A. G. MAYER 213 
genera such as Acropora, Seriatopora, and Pocillopora are killed at 
from 36.2°-37°C., while Siderastrea and some species of Porites can with- 
stand heat up to 38° or even 38.5°C. Generally speaking those forms 
which are sensitive to high temperature are correspondingly affected 
by being smothered under mud, or subjected to the influence of CO2. 
This suggests that high temperature produces death by asphyxiation as 
postulated by Winterstein. There are however some exceptions, for 
certain corals such as Favia fragum and Masandra aereolata die at a 
relatively low temperature but are quite resistant to asphyxiation. It 
appears from experiments conducted at Tortugas, Florida, that some 
corals can adjust themselves to a wide range of metabolic activity and 
can thus survive in a reduced oxygen supply by corresponding lowering 
their metabolic processes. Others, however, cannot effect this adjust- 
ment and must live at a fairly uniform rate of metabolism. 
The more sensitive corals such as Acropora, Seriatopora, Euphyllia, 
or Pocillopora, which are all ofif-shore, pure water forms, are killed by 
being buried eleven hours imder the mud, whereas the shore flat species 
of Porites, Siderastrea, and Maeandra can survive being buried from 
24 to 73 hours. 
The corals of this Australian reef which are never subjected to cold 
can nevertheless withstand low temperature quite as readily as can the 
the corals of the 'cold devastated' reefs of Florida; and conversely 
the Florida corals can withstand high temperatures quite as well as do 
those of Australia. In other words corals are, physiologically speaking, 
of similar constitution whether in the Atlantic or the Pacific ; and natural 
selection has apparently not operated to improve their cold-withstand- 
ing or heat-resisting powers. The reef building forms must live in water 
which is wanner than 15°, and cooler than 38°C. 
It was found that the shallow waters of the Maer Island reef flat 
receive most of their heat by direct radiation from the sun and lose it 
by radiation into outer space at night. Thus at 3 p.m. the water is 
from 1.2° to 6.7° higher than the air, while at 6 a.m. it is from 0.3° to 3°C. 
lower than the air temperature. 
The range in water temperature was thus greater than that of the 
air; for during September and October the extreme range in air tempera- 
ture was only 3.4°C. whereas the water of the reef flat 200 feet from shore 
ranged through 12.5°, and at 1860 feet from shore, in the breakers, the 
range was only 3.5°C. 
Thus the waters of the shore flats within 400 feet of the beach must 
become too hot for coral life during the calms of the ' north west season ' 
between November and April. 
