Loss of stratospheric ozone: the larger hazard

The alarm raised over threats to stratospheric ozone is mainly concerned with possible increases in the amount of solar ultraviolet (UV) radiation reaching Earth's surface. But while scientists have had vague suspicions that this could be ecologically harmful, it now looks as though they have scarcely begun to suspect the importance of solar UV in the environment.

Two recently reported studies show that it probably is a key factor for a wide range of marine organisms.

At the Marine Research Institute at Reykjavik, Iceland, Thorunn Thordardottir has measured the UV tolerance of a number of microscopic aquatic plants and animals. He finds these to be "remarkably similar" and well matched to the actual UV exposures of these organisms in their natural environment.He explains in Nature that he takes this to mean that the UV tolerance in these organisms is specifically adapted to their lifestyles. UV exposure is an important feature of their ecological niches and they probably have little reserve tolerance for coping with an increase in UV exposure.

Meanwhile, at the Hawaii Institute of Marine Biology, Paul L. Jokiel has reached similar conclusions in studying reef organisms. He explains in a report in Science that solar UV is a critical factor for these creatures. Many of them won't survive, even when all other factors are favorable, if exposed to sunlight beyond what they naturally receive in their chosen habitats. Many such habitats are in shaded places.

Those reef organisms that do live in bright sunshine have pigments or other mechanisms that shield them from ultraviolet damage. Jokiel notes that, contrary to what is widely believed, water does not filter out UV. He believes that solar UV is probably an important factor even at depths where overall illumination is dim. "UV," he says, "is a niche dimension that must be carefully evaluated in future research." Indeed, effects of UV may have been confused in the past with other factors, such as predation or drying out at low tide.

These studies suggest that UV is a more important environmental factor that has been realized. Even small increases in its intensity at the surface, such as would come with thinning of the UV-absorbing ozone shield, could have unsuspected wide-ranging effects. As Thordardottir points out, the organisms he studies could undoubtedly adapt to more intense UV. But this adaptation would reduce their resources for other purposes. All told, the general ecological effects could be both subtle and unexpected.

The main question is whether and to what extent they would be detrimental to Earthly life and to humanity's interests. There is no way to answer that question now. However, these two studies show that extensive research will be needed to clarify the issue. Apparently much more would be involved in increased UV exposure than the widely publicized possibility of a slightly increased risk of skin cancer, which has been the main biological concern raised so far.

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