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A Study of Respiration in Alcyonaria

species, temperature, experiments, specimen and jars

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A STUDY OF RESPIRATION IN ALCYONARIA.

Although the respiration of many species of invertebrates has been studied in considerable detail, the only references to that of Alcyonaria which have come to the attention of the writer are those given by Montuori (1913), who studied two species, Alcyameum pallidum and Gorgonia cavolinii. Two records only are given for each species, a small and a larger specimen having been compared in each case. In these experiments the total weight of the colony was taken as the basis of comparison without taking into account the proportion of inert skeletal material—the spicules in the first species and the spicules and chitinous axis in the latter.

Benedict (1915) has emphasized particularly the importance of the proportion of active protoplasmic tissue as shown even in the com parison of individuals of different sexes of the same species.

The observations herein recorded were made as part of a study of the ecological factors determining the distribution of Alcyonaria on the coral reefs of southern Florida. The data from which the amount of living tissue in the several species could be calculated were obtained three years ago in connection with a study of the importance of the alcyonaria as coral-forming organisms (Cary, 1915). A series of exper iments were also carried out on the same species to determine their powers of resistance to increased temperature in order to discover whether or not there is any direct relationship between the rate of respiration and the temperature at which any species is killed; in other words, to determine whether the death of marine animals when sub jected to high temperatures is in reality the result of asphyxiation, as Winterstein (1905) has maintained.

Experimental.

The respiration chambers consisted of museum jars, with clamped tops fitting on rubber gaskets. The capacity of the several jars varied from 960 c.c., to 1,250 c.c. as was determined by weighing each one empty and again when filled with distilled water at a known temper ature. In all experiments with Alcyonaria the displacement of the

specimen was determined and subtracted from the capacity of the jar. Frequently, when it was desired to make several determinations at intervals on the same specimen a fragment of coral rock was allowed to remain attached to the specimen in order to keep it upright during the period between experiments, as these organisms quickly become abnormal if allowed to lie prone on their side on the bottom (Cary, 1914, p. 86). The specimens were kept in a live-car in the intervals between the experiments, so that their condition was normal, as was shown by the fact that the colonies would remain in good condition in this live-car for at least two months.

The sea-water for each series of experiments was brought fresh from the ocean in large aquarium jars and the respiration chambers were filled by submerging them in the large jars. The temperature was controlled by placing the respiration chambers in an aquarium contain ing about 75 liters of sea-water. This aquarium was covered with a black box to exclude the light, as some of the species studied con tained within their tissues enough symbiotic algae (Zofixanthellw) to materially influence the results when the experiments were carried on in the diffuse light of the laboratory. This thermostat was con nected with the running-water supply of the laboratory and during a 2-hour experiment (the usual duration) the temperature would not vary more than 0.2° C. On unusually hot days, when the temperature of the ocean-water over the shallow reef flats was subject to marked fluc tuations, it was found that a much more even as well as lower temper ature was obtained by cutting off the water-supply to the tank, as the early morning temperature of the water would then be maintained within half a degree throughout the day, while the variation during the time of a single experiment would not be measurable with a thermom eter reading to 0.2° C.

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