Plankton form the foundation of aquatic food webs. Plankton are generally found in the upper layer of the oceans in which there is sufficient sunlight to support the photosynthesis of food. Since UV radiation has the ability to penetrate up to 20 metres down in clear water, plankton and other light dependent organisms often experience cell damage, much as human DNA can be damaged by the strong solar radiation. Both plant (phytoplankton) and animal (zooplankton) species are damaged by UV radiation even at current levels. Since UV radiation is absorbed by only a few layers of cells, large organisms are more protected, whilst smaller ones, such as plankton are among the most severely affected by UV radiation. As plankton make up the base of the marine food chain, changes in their number and species composition will influence fish and shellfish production worldwide. These kinds of losses will have a direct impact on the food supply.
UV radiation has also been found to cause damage to the early developmental stages of fish, shrimp, crab, amphibians and other animals. The most severe effects are decreased reproductive capacity and impaired larval development. Even at current levels, UV radiation is a limiting factor, and small increases in UV exposure could result in a significant reduction in the size of the population of animals that eat these smaller creatures.
Research indicates that many plankton species already seem to be at or near their maximum tolerance of UV radiation. Thus, even small increases in UV levels as a result of ozone depletion may have a dramatic impact on plankton life and on entire marine ecosystems. If ozone layer depletion reached 15% over temperate waters in the mid-latitudes, it would take fewer than five days in summer for half the zooplankton in the top metre of these waters to die from the increased radiation. Additionally, large amounts of young fish, shrimp and crabs would die before reaching their reproductive age. Less food would be available for adult fish and other higher forms of marine life, and therefore for human consumption. This is of particular relevance, as more than 30% of the world's animal protein for human consumption comes from the sea.
Effects of the ozone hole in Antarctica have already been seen in some of the organisms. Most of the Antarctic organisms have a low tolerance for UV radiation since for much of the year, hardly any direct sunlight reaches the continent. With the reduced ozone in springtime, UV radiation has been able to penetrate the atmosphere with a higher intensity. Already at the base of the Antarctica food chain an impact has been felt. Increased UV radiation has already reduced the plankton populations by between 6% and 12%. Consequently, species higher up have felt the impact.