Sharks’ plight highlights climate threats

Changes to the oceans affect the Port Jackson shark’s ability to scent food.
Image: Klaus Stiefel via Flickr

Species in the oceans and on land and ice are increasingly feeling the effects – largely for the worst – that climate change and ocean acidification have on their habitats.

LONDON, 20 November, 2015 − Global warming will be bad news for sharks − they will be hungrier, but they may not be able to scent their prey. And climate change already keeps polar bears ashore for an extra 30 days a year, away from their preferred supper.

But Adélie penguins, whose numbers have increased 135-fold in the last 14,000 years as the Antarctic glaciers have retreated, may feel the benefit of a warmer world.

And as Arctic temperatures rise and shrubs and plants colonise Alaska’s North Slope, the moose and snowshoe hare have moved in.

Jennifer Pistevos, a PhD student, and marine ecologist Ivan Nagelkerken, of the University of Adelaide in South Australia, and colleagues write in Scientific Reports journal that they tested the impact of tomorrow’s oceans on the development and behaviour of Port Jackson sharks (Heterodontus portusjacksoni).

Higher temperatures

Under laboratory conditions, the scientists mimicked the sea temperatures and increased oceanic acidity expected as a consequence of soaring carbon dioxide levels in the atmosphere, and higher global temperatures as a consequence of the human combustion of fossil fuels.

Under higher temperatures, the embryonic sharks developed more swiftly. However, the combined effects of warmer water and greater concentrations of dissolved CO2 reduced their metabolic efficiency: that is, they became hungrier. But the same conditions also interfered with the specimens’ ability to smell food. So growth rates fell.

Since the shark is a top predator, such changes could have serious consequences for the ocean ecosystems that they keep in balance. And sharks anyway are in trouble.

“Climate change and ocean acidification are going to add another layer of stress and accelerate extinction rates”

“One third of shark and ray species are already threatened worldwide because of overfishing,” says Sean Connell, a marine biologist at Adelaide, and a co-author of the study. “Climate change and ocean acidification are going to add another layer of stress and accelerate those extinction rates.”

Polar bears, so far, are not threatened. But they are feeling the heat.

Karyn Rode, a research biologist with the US Geological Survey, and colleagues report in the Public Library of Science journal PLOS One that they compared the change in movements of female polar bears fitted with radio collars in the Chukchi Sea, northwest of Alaska, between two periods: 1986 to 1995 and 2008-2013.

Females settle ashore in winter to den and deliver cubs, and also in summer as the sea ice melts – keeping them from the seals that make up the richest part of their diet.

The scientists report that the proportion of bears on land for more than seven days during the summer, from August to October, increased between the two study periods from 20% to 38.9%, and the average stay on land increased by 30 days.

Recent research found no change of body condition, or fall in cub birthrate, so Ursus maritimus for the moment seems resilient. But the trend is not promising: other researchers have warned that the polar bears of the Canadian Arctic may face starvation by 2100.

In contrast, Adélie penguins benefit from the retreat of the ice, as it exposes more land and therefore more available breeding sites.

Population history

Jane Younger, research fellow at the University of Tasmania’s Institute for Marine and Antarctic Studies, and colleagues report in the BMC Evolutionary Biology journal that they examined samples of mitochondrial DNA – inherited only through the female line.

They analysed the population history of Pygoscelis adeliae over the last 22,000 years − a timespan that embraces the peak of the last Ice Age and its ending − and found that, as the ice retreated, Adélie numbers exploded an estimated 135-fold.

East Antarctica is home to 30% of the global population of Adélie penguins, and an estimated 1.14 million breeding pairs use the shores.

But that doesn’t mean global climate change has saved the penguin. Growing numbers will require a greater food supply. “Whether this will be the case in the future remains to be seen, as the impacts of climate change on Adélie penguin prey species, such as Antarctic krill (Euphausia superba), are currently ambiguous,” the authors say.

But on the Northwest Slope of Alaska, thanks to changing climate, the foliage has grown taller. Herbivores have moved north to take advantage of the cover, according to Ken Tape, an ecologist the University of Alaska Fairbanks.

He and colleagues report in Global Change Biology journal that shrub height in the region has increased 78%. And over the last 30 years, snowmelt each decade has happened 3.4 days earlier.

Moose, which were not  seen before 1930, have moved in, and lynx have begun to follow the snowshoe hares, never seen in the region before 1977. − Climate News Network

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