UV damages base of Antarctic food web.

UV damages base of Antarctic food web

Ultraviolet light damages some species of Antarctic plankton much more than others, a new study shows, suggesting that the yearly formation of an ozone hole over Antarctica could alter the region's rich marine ecosystem. However, the study's authors say it remains unclear whether the ozone depletions over the last 10 years have actually harmed life in that area.

Phytoplankton, one-celled floating plants, form a critical base for the oceanic food web. In the Antarctic, they provide the bulk of fodder for krill, a shrimp-like dietary staple of fish, birds and whales.

Deneb Karentz and David L. Mitchell of the University of California, San Francisco, studied nine species of phytoplankton collected from waters near the U.S. station on the continent's Palmer Peninsula. These species are among the most plentiful during springtime, when seasonal stratospheric-ozone losses over the Antarctic begin. The drastic depletions in the ozone layer allow high levels of ultraviolet radiation to reach Antarctic surface waters (SN: 4/15/89, p. 228). In the laboratory, Karentz and Mitchell measured the DNA damage incurred by each species under exposure to ultraviolet light. They also assessed each species' ability to repair damage.

The plankton exhibited a broad range of sensitivity, with the most vulnerable species suffering 100 times as many defects as the most resistant. These results, due to appear in an upcoming issue of ANTARCTIC JOURNAL, were released last week by the National Science Foundation, which partially sponsored the work.

The findings suggest the ozone hole could alter the survival ratio of phytoplankton species, Karentz says. With such a wide variation in species responses, she predicts that the "species that are most resistant are the ones most likely to become abundant."

However, such a change may not harm the ecosystem, observes Robin Ross of the University of California, Santa Barbara. The new data indicate larger phytoplankton species incur less ultraviolet damages than do smaller species, and krill prefer to eat larger phytoplankton, Ross notes. Still, she cautions that krill may depend on smaller species for some nutrients.

Ozone holes, which began forming over the Antarctic in the late 1970s, may already have altered the planktonic eco-system, although biologists have yet to make such a determination. Karentz says attempts to assess the damage are hampered by the lack of species-abundance records for the years before the hole first appeared.