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.