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Toxic Effects Due to High Temperature

corals, oxygen, muricata, hours and sea-water

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The experiments cited below appear to indicate that death from high temperature may be due to the accumulation of acid in the tissues.

Reef corals from Tortugas, Florida, were kept at a constant tem perature in warm ocean-water for 60 minutes in a thermostat, in the dark the temperature remaining constant within about 0.1° C. through out the hour. In this manner the temperature was found that is just sufficient to kill the coral. The results are as follows: °c. ec.

Acropora muricata 34.7 Mteandra areolata 36.8 Orbicella annularis 35.6 Porites furcate 36 . 86 Parkes astrieoides 35.8 Favia fragum 37.05 Porites clavaria 36.4 Siderastrea radians 38.2 It is apparent that those corals which live in cool, relatively agitated water, free from silt, are those that can not withstand high tem peratures, whereas those which live in the hot, silt-laden shallows near shore are, generally speaking, forms which can resist high temperature. Pavia fragum is, however, an exception, for it lives not only in the shal lows close to shore, but also in the pure water of the seaward reefs.

If sea-water be charged to saturation with carbon-dioxide gas from a soda-water siphon, the corals show nearly the same relative resistance to the toxic effect of carbonic acid as they do to high temperature. Thus these corals from least to most resistant are Acropora muricata, Orbicella annularis, Porites astrceoides, P. clavaria, P. furcata, Mceandra areolata, Favia fragum, Siderastrea radians. A. muricata die in less than an hour and S. radians survive for more than 4 hours. In my experiments, however, M. areolata appeared to be slightly more resist ant to than does Porites furcata, whereas the reverse is the case with high temperature; but the two forms are so nearly alike in their reaction that the discrepancy may be due to errors in experimentation or to individual differences of constitution in the specimens, for there is considerable range in this respect. The toxic effect of may, how ever, be independent of asphyxiation, and this supposition is strength ened by the fact that with the exception of Acropora muricata, all of these corals can survive in the dark for more than 11 hours in sea water deprived of oxygen under an air-pump; and even Acropora muricata can withstand 6 hours of this treatment.

It will be recalled that Henze (1910) found that sea-anemones con sume less oxygen as the oxygen in the surrounding sea-water is reduced ; and in 1917 McClendon discovered that the medusa Cassiopea can live in the dark for more than 7 hours without oxygen and under this con dition it produces no appreciable amount of CO:. In other words, these coelenterates can, if deprived of oxygen, suspend their metabo lism for a more or less protracted period without apparent injury.

Moreover, I find that a constant high temperature causes death in the same time, whether the sea-water surrounding the corals has the normal concentration of about 4.3 c.c. oxygen per liter, or the oxygen be supersaturated at 6.6 c.c. per liter, or reduced by being placed under an air-pump to 1.7 c.c. per liter. Apparently, therefore, there is no direct relation between the oxygen supply and the death temperature. The death temperature also remains the same whether the corals be in sunlight or in darkness.

Using Winkler's method, tests were made upon five of the common reef corals of Tortugas to determine their relative rates of consump tion of oxygen. In these experiments the corals were kept in the dark to prevent photosynthesis in their commensal plant-cells, for in sun light the surrounding water soon becomes supersaturated with oxygen from this cause. Care was also taken to use very small specimens of the various species of corals and to place them in large glass jars her metically sealed, each containing about 2 liters of sea-water. The corals were kept for 5 hours in these jars in darkness in a water thermo stat at 28.5° C. and daily experiments were made upon each of them for 11 successive days. The polyp-bearing area of each coral was then determined by a planimeter and the relative weight of living substance per square centimeter was obtained by killing specimens of these corals in formalin, hardening in alcohol, and then dissolving away the cal careous substance in nitric acid and weighing the tissue in sea-water. Prepared in this manner a square centimeter of the animal substance of Acropora muricata weighs 0.032 gram; while Orbicella annularis weighs 0.17, Favia fragum 0.059, Mceandra areolata 0.109, and Siderastrea radians 0.125 gram per square centimeter.

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