Climate warming spells life for algae, but death for giant spiders

Climate warming is affecting Antarctic waters, threatening the survival of fragile plants and animals living on the frozen continent. If predictions from global climate models are correct, the prospects for cold-blooded marine animals such as giant sea spiders are bleak, says a biologist with British Antarctic Survey. But the news isn’t all bad, with some algae set to thrive in warmer waters.

Average temperatures in the Antarctic have risen by around 1ºC over 15 years, Professor Lloyd Peck told an audience at the BA Science Festival, and in response, microalgae and nutrients in the water have doubled.

According to a recent study published in Science, the environmental and ecological characteristics of lakes in the Antarctic are now changing as fast, if not faster than any site on earth.

Temperature change is not a problem for most Antarctic lake organisms. “Species living there have great biological flexibility, with some being able to survive temperature down to -25ºC as eggs in winter and up to +25ºC as adults in summer,” says Peck. “The real problem for many such species in a changing environment is not coping with the change, but surviving competition from invasions by alien species from lower latitudes.”

But for the marine environment, temperature changes spell trouble. Antarctic marine waters have the most constant temperature on earth, with some sites experiencing temperature variations of only 0.1ºC throughout the year, says Peck. Signy Island, the focus of the study, is one of the most variable in the Southern Ocean, but even there annual temperatures vary by only 1.5ºC annually. Unlike the Antarctic lakes that are relatively young in evolutionary terms, marine conditions have existed for 10-15 million years.

Professor Peck’s concern is that cold-blooded marine animals living in the Antarctic sea can’t cope with excessive temperature change. “Experiments show that most have upper lethal temperatures between +4ºC and +10ºC. Their ability to survive long-term temperature rise for periods of weeks to months is even lower, typically 3ºC to 6ºC,” he explains.

Current models predict that global sea temperature will rise by around 2ºC in the next 100 years (Hadley Centre model III). Summer temperatures in the Antarctic seas often peak at 1ºC, says Peck. “A rise of 2ºC will elevate temperatures to those that compromise animal capability, at a time when restricted summer food supplies are available and many species need to feed.” Marine species are thus highly vulnerable to climate change, and their isolation in the Antarctica leaves them no option to migrate.

“Many cold-blooded species in Antarctica grow to giant size, because of the high levels of oxygen present in cold-water environments. This includes sea spiders over 30 cm across and isopods, the relatives of woodlice, over 13 cm long, It would thus appear that some of the worlds most exotic and impressive marine species are amongst the most fragile in the face of predicted rising temperatures,” concludes Professor Peck.

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