IMPACT OF UV RADIATION ON THE AQUATIC ENVIRONMENT - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 173

much atmospheric carbon as all terrestrial ecosystems taken together, which amounts to
100 gigatons in terms of carbon dioxide 1 . Marine ecosystems play an overwhelming role
in the productivity since they represent 99.5 % of the water surface. In these ecosystems
phytoplankton are the dominant biomass producers, but macroalgae also have a
significant share in the biomass productivity although they are restricted to coastal areas
and the continental shelves 2 . Macroalgae form the basis of an intricate food web, serve
as shelter for larval fish and crustaceans and have a significant economic importance
since several hundred thousand tons of seaweeds are harvested every year for food
production and technological exploitation.
During the last two decades dramatic stratospheric ozone depletion has been
observed over the Antarctic continent 3 . Several years later, this was also found over the
North pole 4 . Significant decreases in total ozone column are also recorded at high and
mid latitudes with concomitant increases in solar UV-B radiation (280 - 315 nm, C.I.E.
definition) at the Earth's surface 5 . These trends are predicted to continue well into the
current century with a return to pre-80s levels by the year 2065.
The high energetic short wavelength radiation affects most forms of life on this
planet. It is responsible for increased incidences of skin cancer in humans, higher rates
of cataracts, immunosuppression as well as other diseases. UV-B has been reported to
affect terrestrial and aquatic ecosystems and may have significant consequences for the
chemistry of the troposphere (e.g. photochemical smog formation) and biogeochemical
cycles 3 . Solar short wavelength radiation penetrates deep into the water column of many
freshwater and marine ecosystems, where primary productivity occurs in the euphotic
zone 6-7 . Growing evidence indicates that further ozone depletion will impair light-
dependent responses of aquatic primary producers, such as photosynthesis,
photoorientation and photoprotection 8 .
Significant increases in solar UV may affect biomass productivity in aquatic
ecosystems with negative consequences for all levels of the intricate food webs and food
production for animals and humans 9-10 . Further consequence may be changes in species
composition and ecosystem integrity.
Aquatic ecosystems are important global sinks for atmospheric carbon dioxide,
and decreased biomass productivity causes reduced sink capacity for CO 2 11 which
consequently has negative effects on global warming 12 .
3. Cyanobacteria
Cyanobacteria are an evolutionary ancient group of prokaryotes which possess
oxygenic photosynthesis that closely resembles that of higher plants. However, they
lack chlorophyll b and plastid envelopes but contain phycobiliproteins as accessory
pigments which are organized in high molecular-weight phycobilisomes located on the
outer thylakoid surface like in red algae. Cyanobacteria are key players in both
freshwater and marine aquatic ecosystems and can constitute up to 40 % of marine
biomass. Furthermore, many cyanobacteria can fix atmospheric nitrogen either as
individual organisms or in symbiosis with many other species including protists,
animals and plants 13 . Only prokaryotic organisms are able to use atmospheric nitrogen;
all other organisms take up nitrogen in the form of nitrate, nitrite, ammonium or organic
compounds. In rice paddy fields cyanobacteria are of high importance as a biological