Under the ice
Dr miles lamare has spent six weeks of each of the last four years in—and under—Antarctica. A lecturer in the Department of Marine Science at the University of Otago, Lamare has been diving under the sea ice to see how marine invertebrates such as the sea urchin Sterechinus neumayeri and the starfish Odontaster validus (the red seastar) are handling the increase in solar ultraviolet radiation to which they have been exposed as a result of the hole in the atmosphere’s ozone layer. Lamare is particularly interested in effects on the small, free-swimming larval stage that most marine invertebrates undergo.
Unfortunately, it seems that the sea urchins and starfish aren’t doing too well. And as they are significant elements in Antarctica’s marine biomass, a depletion in numbers, says Lamare, could lead to considerable changes in the ecosystem.
Lamare and his colleagues lower themselves into the coldest water in the world at a place called Cape Armitage, a 30-minute drive by Piston Bullys (a rubber-treaded vehicle for travelling over snow) from Antarctica New Zealand’s Scott Base. Set atop the sea ice, and kept warm by a kerosene heater, is a 2 x 4 m hut. Inside, a hole has been drilled through the 2 m thick ice, through which the dry-suited scientists descend.
The hole in the ozone layer was discovered about 30 years ago and is expected to persist for at least the next 50 years. During that time, plenty of organisms (as well as humans living at high latitudes) will be subject to damage—including structural damage to DNA—by UV radiation that was once more completely blocked from reaching the ground by ozone high in the atmosphere. (Ozone, considered a pollutant at ground level, is a colourless gas with a chlorine-like odour. It is an allotrope of oxygen, with the formula 03.)
Some marine organisms produce “sun-screen” compounds that absorb the most dangerous wavelengths of UV radiation. But other creatures—and it turns out S. neumayeri is one—have not.
It used to be thought that the sea ice that surrounds most of the Antarctic coastline during the summer months provided the organisms that live below it with ample protection from UV radiation. And perhaps creatures like the nearly transparent S. neumayeri larva didn’t need sunscreen anyhow. But research completed by Lamare and his colleagues in 2004 showed that UV radiation was in fact getting through the ice; and, importantly, that UV-B rays—the ones that tend to cause structural damage to DNA (and melanoma in humans)—were penetrating the ice with sufficient intensity to cause developing organisms harm.
Lamare, together with Prof. Michael Lesser, from the University of New Hampshire, in the USA, found that UV-B radiation was not only causing significant mortality of larvae and embryos, but was also damaging the DNA of the embryos that survived. Rates of mortality and the extent of DNA damage varied from one year to the next, depending on fluctuations in the severity of the hole in the ozone. Why, Lamare and his co-workers wondered, was S. neumayeri so sensitive to UV-B?
For most organisms, damage to DNA is not necessarily fatal (or even serious), as enzyme-mediated mechanisms can repair the lesions. Once Lamare had figured out the sea ice wasn’t affording the sea urchins any protection, he began analysing their rate of DNA repair. It proved to be pretty sluggish.
Photolyase is the enzyme that repairs the lesions most often caused by UV radiation. But if this isn’t present, or isn’t working properly or fast enough, an organism can’t repair all the damage. This appears to be the case for S. neumayeri. Lamare wondered whether water temperature was also having an effect on the urchin’s enzyme repair mechanism. For comparison, during the summer of 2005–06 he gathered data from sea urchins elsewhere, including members of the genera Evechinus in Fiordland and Diadema on Australia’s northern Queensland coast.
It was important, he says, to get a temperate and tropical comparison in order to deduce whether enzyme activity differed according to temperature: were the Antarctic larvae “suffering” more because it was so cold where they lived and the enzyme couldn’t work to full effect?
“Enzyme activity is generally susceptible to cold temperatures,” says Lamare. “Enzymes are proteins that must flex and un-fold to carry out their job. In cold water, enzymes become rigid and less flexible, which inhibits their normal activity. Organisms that live in cold water have to modify their enzymes so that they become more flexible and compensate for the cold.”
It appears that temperature compensation isn’t one of S. neumayeri’s strong suits. Thus, while photolyase in the Australian urchins repairs the damage to DNA caused by UV radiation (which the animals are exposed to all year-round), the same enzyme in the urchins in Antarctica doesn’t do nearly as good a job, suggesting that it hasn’t been modified for operation in a cold–water environment.
This isn’t altogether surprising. Lamare explains that organisms such as S. neumayeri have been isolated in the Antarctic for about 20 million years, during which time they have evolved under relatively low levels of UV-B radiation and so may not have needed to repair the kind of damage it can cause.
“The Antarctic larvae have a very sensitive metabolism. With an increase in ultraviolet radiation,” says Lamare, “the Antarctic species is really vulnerable. It can’t repair its DNA, because it has an enzyme that hasn’t adapted to the cold. Now we’re trying to figure out why.”
Research is continuing into this question, not only at Scott Base but also at Lamare’s regular place of work at the University of Otago’s marine laboratory at Portobello. Lamare has imported live Antarctic sea urchins and starfish, which now spend their days living at –1.0° C in a large freezer. He is currently focusing his efforts on how the structure of photolyase differs between Antarctic and non-Antarctic species. This includes identifying and examining the gene that codes for it.
Antarctica New Zealand’s science-strategy manager, Dean Peterson, is supportive of the work done by Lamare and his team. “New Zealand is intensifying its commitment to research in the Southern Ocean,” he says, adding that Antarctica New Zealand plans to increase the amount of marine research undertaken at Scott Base and in the Southern Ocean.
“Global climate change, particularly in the Antarctic and Southern Ocean, is a significant focus of both national and international scientific attention,” says Lamare. The results of his work will not only allow predictions of the effects of UV-B radiation on Antarctic marine invertebrates, but will also show how susceptible to future environmental change these species may be in view of their geographical isolation and long evolution in the Antarctic environment.