Possible Influences of Solar Uv Radiation in the Evolution of Marine Zooplankton

Evolution is understood to be a species' total response to a large number of environmental factors. One of these factors, even in the sea, may be solar UV radiation. If so, one might relate a number of unique features of marine zooplankton to the selective pressures of this near-surface stress. Some characteristics of marine zooplankton that may have been influenced or even determined by UV radiation are the diel vertical migration, certain seasonal migrations and the seasonal occurrence of near-surface larvae, UVabsorbent cuticles, zooplankton coloration, zooplankton associations, and zooplankton shapes. The environment has always changed and presumably it will continue to change. Change is also a fundamental aspect of living matter. Morphological and behavioral variability are the raw materials which allow better adapted organisms to survive environmental changes. Recent discussions of the development of life have pointed to UV radiation as a major limiting factor on the early earth (Sagan, 1973; Caldwell, 1979). That solar ultraviolet radiation has played some subsequent part in the evolutionary selection process on land is evident in the protective coverings and avoidance behavior of many terrestrial organisms. Organisms have also responded in an evolutionary sense to infrared radiation (heat), and in many cases it would be difficult to separate the effects of these two spectral extremes. UV radiation has not until recently been believed to be of consequence in the oceans, so that studies on morphology, behavior, and horizontal, vertical, and seasonal distributions of marine organisms have not generally explored possible relationships to solar UV. That UV radiation enters the