Effects of Ozone Depletion in Marine Ecosystem

Aquatic ecosystems contribute more biomass (104 Gt/a) than all terrestrial ecosystems (100 Gt/a) combined. Recent work on UV-B effects has concentrated on inhibition mechanisms and field studies in the subpolar waters of Antarctica, because of its high productivity and the occurrence of the ozone hole over this region.

Phytoplankton organisms orient within the water column using external factors. However, mobility and orientation mechanisms are impaired by UV-B radiation. Because most organisms do not possess UV-B receptors, they cannot avoid deleterious wavelength radiation that (according to new measurements) penetrates deeper into the water column than what has been previously measured. New action spectra indicate that, in addition to DNA, other targets absorb UV-B radiation including intrinsic proteins of the photoreceptor and photosynthetic apparatus.

The inability to adjust their position within the water column causes massive inhibition of photosynthesis, measured both in field and laboratory studies. Only in a few cases have potential UV-B-inducible screening pigments been identified.

A large share of the nitrogen consumed by higher plants is made available by bacterial microorganisms, which have been found to be very sensitive to UV-B radiation. Losses in nitrogen fixation could be compensated by additional nitrogen fertilization. However, such actions could stress the capabilities of developing nations.

The role of DMS, released from plankton and macroalgae as aerosol and cloud nuclei, is of major concern. Most importantly, a UV-B-induced decrease in phytoplankton populations may have an impact on cloud patterns and concomitant global climate changes.

An increased understanding of Antarctic trophic dynamics suggests that the likelihood of direct UV-B radiation effects on consumers is small. Rather, it is the possibility of indirect effects that may significantly affect the Antarctic trophic structure, such as different species sensitivities to UV-B radiation, or decreases in total available primary production. Because more than 30% of the world's animal protein for human consumption comes from the sea, the human populations may also be affected by the direct and indirect consequences of increased solar UV-B radiation on aquatic food webs.

Another potential consequence of a decrease in marine primary productivity would be a reduction in the capacity of the ocean to absorb carbon dioxide. A hypothetical loss of 10% of the marine phytoplankton would reduce the oceanic annual uptake of carbon dioxide by about 5 Gt (an amount equal to the annual emissions of carbon dioxide from fossil fuel consumption). Uncertainties regarding the magnitude of increased levels of UV-B radiation on aquatic systems still remain, including problems of extrapolating laboratory findings to the open sea, and the nearly complete absence of data on long-term effects and ecosystem responses. Uncertainties and future research needs include adaptive strategies and the effects of cumulative UV-B radiative doses. Additional information is needed in several areas before a more reliable assessment of risks is possible.


Current data suggest that predicted increases in UV-B radiation could have important negative effects on the marine environment. However, uncertainties regarding the magnitude of these effects still remain, including problems of extrapolating laboratory findings to the open ocean, and the nearly complete absence of data on long-term effects and ecosystem responses.

Planktonic marine organisms account for over half of the total global amount of carbon fixed annually (10[11] tons). Any reduction in this productivity will undoubtedly affect global food supply and global climate. Both primary production and subsequent steps in biological food webs are sensitive to current UV-B levels, and are potentially endangered by expected increases in UV-B radiation.

UV-B radiation affects 1) adaptive strategies (e.g., motility, orientation), 2) impairs important physiological functions, (i.e., photosynthesis and enzymatic reactions), and 3) threatens marine organisms during their developmental stages (e.g., the young of finfish, shrimp larvae, crab larvae). In addition to DNA damage, UV-B radiation affects enzymes and other proteins, eliciting photodynamic responses. These effects can have a number of possible consequences for aquatic ecosystems:

• Reduction in biomass production, resulting in a reduced food supply to humans;

   

• Change in species composition and biodiversity;

   

• Decreased nitrogen assimilation by prokaryotic microorganisms, possibly leading to a drastic nitrogen deficiency for higher plant ecosystems, such as rice paddies; and

   

• Reduced sink capacity for atmospheric carbon dioxide, thereby augmenting the greenhouse effect.

A number of marine systems, particularly some fisheries (which are severely depleted due to over-harvesting and pollution), are presently stressed by anthropogenic factors. Coral reefs (important to both fisheries and tourism) are under stress and are experiencing declines from sedimentation, pollution, and perhaps temperature increases. Increased UV-B radiation may push some populations past their threshold by decreasing larval fish survival or increasing coral bleaching events.