Banner image: Penguins on the hunt for krill in the Southern Ocean. (Photo credit: John Weller Photography)

At the heart of their Antarctic habitat, the krill population is projected to decline by about 30% this century due to widespread negative effects of human-made climate change. However, by the end of the 21st century, these effects on this small but significant species will be largely indistinguishable from the natural variability of the region’s climate, finds new CU Boulder research.

The study, published today in Frontiers in Marine Science, has important implications not only for the local food web, but also for the largest commercial fishery in the Southern Ocean: a booming fish oil industry valued at $ 2 billion as an omega-3 supplement in retail giants like. is sold at cost co.

Above: Antarctic krill Euphausia superba. (Photo: Uwe Kils / Wikipedia) Below: Omega-3 oil pills, the product of a booming $ 2 billion fish oil industry. (Image credit: PxHere)

“Krill connects the ecosystem together,” said Zephyr Sylvester, lead author of the paper and a PhD student in environmental studies. “They’re really important to pretty much every species of predator in the Southern Ocean.”

Since these tiny animals live in one of the most sensitive areas in the world to climate change, explicitly separating trends related to man-made warming from those that naturally occur in the krill habitat is a crucial step in planning and mapping Harvest limits.

This study is also the first of its kind to use a group of climate models to show that climate change has the potential to dramatically alter Antarctica’s marine ecosystems, but that natural climate variability can obscure man-made trends.

Small but important

Krill are about 6 cm long, fast-swimming zooplankton that live in large groups. They are the key to the region’s food chain and are eaten by almost everything that lives in the waters around Antarctica: penguins, seals, fish and whales, some of which are still recovering from overfishing in earlier centuries.

But while they are one of the most abundant species on earth – their total biomass is estimated at 300 to 500 million tons – krill can only survive in a narrow range of temperatures and is heavily influenced by variables in their underwater environment.

Currently, fisheries in the Southern Ocean are managed by the Convention for the Conservation of Antarctic Marine Living Resources known as CCAMLR (pronounced “cam-ah-lar”), an international body established as part of the Antarctic Treaty System.

The first item on the agenda? Krill. But 40 years after its inception, their catch limits for this creature are still only set based on a stock assessment that does not take into account natural variations in the environment or the effects of climate change.

While it is now widely recognized internationally how important it is to understand the effects of climate change on this marine ecosystem, understanding natural climate variability is an important prerequisite, according to Sylvester.

“What we really need to understand is, is there enough krill to feed everything that is needed in the Southern Ocean and also for humans to eat?” Said Cassandra Brooks, co-author of the article and assistant professor of environmental studies. “My hope is that we can do this as a first step in understanding how to better manage krill.”

    Lara Asato)

Gentoo penguin feeding its chick krill. (Photo credit: Lara Asato)

What is natural variability?

Every environment on earth, of course, varies a little each year in terms of weather, temperature, and rainfall. For example, some Colorado winters have more snowfall and others less. Some get a little warmer, some get colder. Aside from man-made climate change, the state exhibits a unique pattern of precipitation and temperature each year due to natural fluctuations.

However, separating the effects of man-made climate change from the natural changes in a region is not an easy task. To pull apart the variables that influenced the Southern Ocean this century, the researchers performed many times a larger set of models known as the large ensemble Earth system model. It is the first time this has been done for the Southern Ocean and for krill.

“Then we could look at the various trends and quantify how much the natural variability obscures the signal for climate change,” says Sylvester.

This research addresses one of the biggest gaps between scientists and fisheries managers: understanding and communicating uncertainty. By being able to quantify how much change is likely to occur due to natural variability and regardless of climate change, Brooks says it enables everyone involved to better plan for the future and preserve krill for those who depend on it.

“Even if we won’t see this really strong signal of climate change until later, it is important for us to understand that the Southern Ocean is a very dynamic system and that we absolutely have to deal with natural variability,” said Brooks. “And we should be ready to respond to the wider effects of climate change.”

Matthew Long of the National Center for Atmospheric Research is co-author of this paper.

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