THE EFFECT OF THE ULTRA-VIOLET COMPONENT OF THE SUN'S RADIATION UPON SOME AQUATIC ORGANISMS

Abstract

Specimens of three species of fresh-water entomostracans—Daphnia pulex, Daphnia magna and Cypris reticulate—were each exposed to sunlight which had passed through filters which transmitted different regions of the solar spectrum. One filter ("Total") transmitted both visible and ultra-violet radiation, a second ("Novial") transmitted the visible only and a third ("U.V.") transmitted only the ultra-violet. By prolonged exposure the animals were killed under the Total and U.V. filters, while under the Novial they lived indefinitely. The chief point of interest lies in the comparison of the results obtained with these entomostracans which live in shallow pools with the results of previous experiments (2) on three marine entomostracans which remain at a considerable depth in the sea when the illumination is at all intense; the comparison shows that the former have a far greater resistance to the lethal effects of the sun's ultraviolet radiation. Developing embryos of the squid, Loligo pealii, were experimented upon in a similar manner; these embryos, which are enclosed in a gelatinous matrix attached to large algae in the intertidal zone, and, at low tide, are exposed to full sunlight, were extremely resistant to ultra-violet radiation.