An increase in incident solar ultraviolet irradiation, resulting from possible deterioration of the stratospheric ozone layer, would have important biological effects. Though the oceans are relatively opaque to UV radiation, compared to visible light, increases in incident UV may affect organisms living within the first few meters of the sea surface.Shrimp larvae, crab larvae, and euphausids were exposed to various low levels of simulated solar UV radiation (UV-B, 290-315 nm) under laboratory conditions. Comparisons between solar and artificial spectra were based on spectroradiometric measurements converted to erythemally effective irradiance. These zooplankton tolerated UV-B irradiance levels up to threshold levels with no significant reduction in survival or developmental rates compared to control organisms. Beyond the threshold levels, activity, development, and survival rapidly declined. The apparent UV thresholds are near present incident UV levels.Observed survival threshold levels for each experimental group were superimposed on seasonal solar incident UV levels at the experimental site. These threshold levels appeared to be exceeded by median ambient UV levels late in the season of surface occurrence of each species. UV increases resulting from ozone depletion may significantly shorten this season. Although the apparent impact would be lessened by the decrease in UV with depth, irreversible detrimental effects would probably occur before reported survival thresholds were exceeded.

Previously reported thresholds for UV-B dose and dose-rate were determined under artificial light regimes using more than an order of magnitude less visible light than found naturally. Near-UV and/or visible light is needed for photoreactivation, and the accuracy of earlier findings may have been influenced by less than maximum photorepair in the laboratory. Experiments with shrimp larvae and adult euphausiids, comparing survival at various UV-B doses and dose-rates combined with different levels of near-UV and visible irradiance, suggest that photorepair occurs in these organisms. Further, this apparent photorepair reaches maximum levels at relatively low visible light intensities.Previously reported tolerance limits for shrimp larvae and adult euphausiids were confirmed (in particular, the relationship between dose/dose-rate safe and lethal limits in shrimp). Also, the earlier experimental design did not appear to have affected these limits since additional near-UV and visible light did not substantially alter the results.In experiments using a 44-1 plastic cylinder (140-cm water depth), adult euphausiids successfully avoided moderate UV-B combined with visible light, but were attracted to and ultimately killed by higher levels of UV-B combined with low visible light. The apparent inability of euphausiids to directly detect harmful levels of UV-B irradiance would become an important factor in a new solar spectral distribution caused by ozone depletion.