Warmer ocean temps could affect productivity
By Summit Voice
FRISCO — A new study suggests that global warming could cut krill habitat by 20 percent — and more in some critical areas where land-based animals like penguins and seals depend on the tiny crustaceans for food.
“Each year, growth of Antarctic krill in the Southern Ocean produces new material that weighs twice as much as all the sugar produced in the world,” said lead author, Dr. Simeon Hill, a marine biologist at the British Antarctic Survey.
“Krill grow fastest in cold water and any warming can slow down or stop growth, reducing the food available for wildlife. Our research suggests that expected warming this century could severely reduce the area in which krill can successfully grow,” Hill said.
“The areas that will experience temperature changes that will be detrimental to krill growth are in a band of the ocean called the antarctic circumpolar current; it’s within this band of water that we think will see the majority of habitat loss,” he said.
Antarctic krill are the primary food source for many species of whales, seals, penguins and fish. They are sensitive to sea temperature, especially in the areas where they grow as adults. That sensitivity, along with the increased harvesting, has prompted scientists to try to understand how they might respond to the effects of further climate change.
To try and predict that response, the scientists gathered krill samples to time their growth rate under different temperature regimes, Hill said. That information was combined in a model with projections of sea surface temperature increases, helping the team map out the potential impacts.
“There’s a hell of a lot of ocean out there, but it’s not all the same. The ocean has structure,” Hill said. Krill can travel thousands of miles in a lifetime, but they require specific conditions to successfully hatch and develop from eggs, he explained.
The modeling results suggest some the biggest impacts will be felt where there is important foraging habitat for seals and penguins living on South Georgia Island, which harbors abundant and diverse wildlife populations.
Around South Georgia Island, krill habitat could be reduced by as much as 55 percent. The scientists said animals which don’t travel far to forage, such as fur seals, would be most affected by the projected changes.
Specifically, the study looked the likely impact of projected temperature increases on the Weddell Sea, Scotia Sea and Southern Drake Passage, which is known for its abundance of krill. This region has experienced sea surface warming of as much as 1 degree Celsius in the past fifty years, with another degree of warming likely by 2100.
In early life stages, krill require deep water with low acidity and a narrow range of temperatures for their eggs to successfully hatch and develop. The larvae then feed on algae on the underside of sea ice.
The adults require suitable temperatures and enough of the right type of food (larger phytoplankton) to successfully grow and reproduce. Many of these critical environmental features (temperature, acidity, sea ice and food availability) could be affected by climate change.
Krill is also being commercially fished, although there is nothing to suggest current levels are unsustainable. In fact, at less than 1 percent of estimated biomass, catches are much lower than most other commercial fisheries.
But the Antarctic krill fishery took 68 percent of its total catch between 1980 and 2011 from the area of projected habitat degradation. The study suggests improved management systems to ensure the fisheries take into account both growing demand for catches and climate change.
Although there is evidence that warming seas pose a threat to Antarctic krill habitats, the team of researchers believe this can be mitigated with effective fisheries management systems in place.
The larger, long-term dynamics of krill populations are still poorly understand. Consistent monitoring in the remote Southern Ocean isn’t easy, and the observational record doesn’t span a huge amount of time, making difficult to separate natural variability from immediate impacts like commercial krill fishing or inreased sea surface temperatures.
But satellite data helps establish an accurate record of sea surface temperatures and offers clues about basic biological productivity in the region, showing the extent and timing of phytoplankton blooms.
At least some of that data suggests there is an emerging question as to whether the right kind of food is available to krill at the right time and the right place, Hill said. Other than that, there’s no sign of a drastic change in populations in the past we decades.
“But we’re warning it’s not a time to be complacent,” Hill said, explaining that the abundant wildlife of South Georgia Island could be at risk.
“They’re foraging in the areas that are going to be worst affected … the areas that are most vulnerable to the projected changes,” he concluded.
Filed under: Antarctica, biodiversity, climate and weather, Environment, global warming Tagged: | Antarctic krill, biodiversity, British Antarctic Survey, climate change, Environment, global warming, krill, Plymouth Marine Laboratory, Southern Ocean, Weddell Sea