Effects of increased UVB radiation on Antarctic marine microalgae

NATURAL UVBR CAUSES DNA DAMAGE IN ANTARCTIC MARINE PHYTOPLANKTON
POPULATIONS.

ANITA G.J. BUMA, M. K. DE BOER, W.W.C. Gieskes

UVBR stress in Antarctic marine phytoplankton was studied under
natural irradiance conditions. During a research period of 3 months at
Rothera Station (67S, British Antarctic Survey) data were collected
regarding UVBR penetration, using a biochemical dosimeter, based on
the induction of DNA damage (cyclobutane pyrimidine dimers, CPD's) in
bare DNA. Furthermore, UVBR induced DNA damage was studied in several
size fractions of natural phytoplankton populations. Finally,
incubation experiments were conducted to study wavelength dependent
rates of DNA damage induction as well as repair.

The results show that in the Rothera Bay area attenuation of
biologically effective UVBR is fast, likely due to the presence of
phytoplankton (mainly diatom) blooms, giving 1 BED (Biologically
Effective Dose) levels between 5 and 8 meters. In most cases, damage
levels decreased with depth in all size fractions. The smallest size
fraction (0.2 - 2 mm) gave the highest damage levels in all cases.

CPD's were solely induced by UVBR, and exposure to natural solar
radiation induced several tens of CPD's (per million nucleotides)
within hours, mainly in the smallest size fraction. Repair of damage
was visible when populations were exposed to UVAR + PAR, but not with
PAR alone, indicating that highest photolyase activity is taking place
in the mid UVAR region.

The results clearly show that phyto- and bacterioplankton from marine
Antarctic systems suffer from UVBR stress under natural, non-ozone
depleted conditions. It also indicates that the smallest organisms,
i.e. bacteria are more vulnerable for DNA damage induction than larger
phytoplankton cells, as found elsewhere. It is presently not known how
these differences in vulnerability affect food web dynamics in marine
Antarctic waters.