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Biodiversity

A transforming ecosystem: Chukchi and Bering Sea

Article: Huntington, H.P., Danielson, S.L., Wiese, F.K. et al. Evidence suggests potential transformation of the Pacific Arctic ecosystem is underway. Nat. Clim. Chang. (2020).

Even though we constantly hear about climate change, we still do not understand how exactly and to what extent it affects our ecosystems. That is because ecosystems do not respond in a simple fashion. Instead, various components interact in a sophisticated manner that is difficult to predict. Hence to get a complete picture, it is essential to look at how different elements react to a change instead of studying just a few.  In one such study, Huntington et al. looked at the effects of increasing temperature on various components such as phytoplankton, migratory birds, mammals, hunting communities of the Chukchi and Bering Sea Ecosystem.

Understanding the Chukchi and Bering Sea Ecosystem

 

Fig. 1 Satellite image showing northern Bering and Chukchi sea-ice conditions on 2 June 2017

Chukchi sea in the Pacific Arctic is one of the most productive regions in the world oceans (Fig. 1). During spring and summer, the ice melts and allows nutrient-rich waters from Bering Strait into the Chukchi Sea. Nutrient-rich waters result in phytoplankton blooms that form the base of the food web. Some of the phytoplankton escape grazing by zooplankton and fish in the water column and settles on the sea surface, serving as food for the organisms living on the seafloor like sea squirts and worms. The region is also home to nesting, migratory birds, and other marine mammals that support the indigenous coastal communities in the area. During autumn and winters, the ice formation reduces the flow of nutrient-rich waters to the Chukchi and limits the migratory birds, seals, Pacific walrus, and whales to the Bering Sea.

How is the ecosystem changing?

In recent years the Chukchi-Bearing Sea ecosystem has started to deviate from what we knew about it. Sea Ice is excellent at reflecting most of the sunlight falling on it and keeps the surroundings cool. Less sea ice means less reflection and greater absorption of sunlight which results in warming and accelerates the melting. In recent years warming has increased the amount of nutrient-rich waters flowing into the Chukchi Sea, as it remains ice-free for a good part of the year. Warming has also led the migratory birds and mammals to move northwards. For the hunting communities, the opportunities dependent on the presence of sea-ice have decreased or shifted in time. Arctic mammals such as seals and walruses use sea-ice as a platform to rest and nurse their young, this makes it easier for hunters to get them. But at the same time, the lack of sea ice in autumn and early winters has allowed additional whaling as less sea-ice opens up the Arctic to less ice adapted humpback, fin, and killer whales.

In addition to worldwide warming, the Arctic Pacific saw unusual warming in 2017. During the winter of 2017, the ice was observed only up to the Bering Strait, and the Bering Sea remained ice-free. The summer of 2017 also saw much warmer waters in the Bering Sea. Similar observations were made in 2018 and 2019. The authors of this study looked at the published and unpublished data on phytoplankton, migratory birds, fish catch, hunting communities, mammals, etc., from 2018 and 2019. To assess whether the changes in the ecosystem due to 2017 warming have persisted in 2018 and 2019.

Changes due to unusual warming

Bowhead whale (NOAA, Fisheries)

In the spring of 2018, phytoplankton bloom was delayed in the Bering Sea due to the lack of fresh water that comes from melting ice. But at the same time, the northern Bering Sea saw premature ice melt and hence an early bloom. Unfortunately, a bloom doesn’t always mean an excess of food. Due to the change in the timing and conditions of the bloom, the toxic phytoplankton species sometimes replace the usual phytoplankton species. Scientists found saxitoxin and domoic acid in the water samples and walruses harvested from the Bering Strait. These compounds are toxins released by some phytoplankton to protect themselves from grazing and have led to food safety concerns for the indigenous communities. The organisms, like copepods that feed on phytoplankton, also declined in numbers. The fishes and seabirds moved northwards into the Chukchi Sea due to the lack of sea-ice. The total numbers of seabirds declined in the Bering Sea as higher numbers were spotted in the Chukchi Sea.

 

Spotted seal pup (NOAA, Fisheries)

Now moving to the mammals, the scientists saw bowhead whales near Alaska, which is to the north of Chukchi Sea, nearly a month earlier than usual. These whales spent their winters in the Chukchi sea instead of their typical winter habitat in the Bering Sea. Smaller and weaker spotted seal pups were found during these years, and a lot of seal carcasses belonged to young and starved pups. The scientists attribute this mortality to lower food quality; even though fish like Salmon and Arctic Cod increased in numbers, they weren’t as nutritious.

 

Such changes may not be brief; instead, they may be a sign of what is to come.

The effects of the unusual warming persisted in 2018 and 2019. This interdisciplinary study points towards the opportunity to study the changes as they unfold rather than reconstructing them later. Even though the effects of unusual warming in 2017 may slowly wean off, they give us a glimpse into what is to come if the planet continues to warm. The authors point out that the Arctic ecosystem will most likely transform into a subarctic ecosystem; that is, the Chukchi Sea may resemble the Bering Sea though some differences will exist. As the sea-ice recedes some species will cling to their typical habitat while others will shift and severely affect the quality and the quantity of food. The major takeaway is to continuously monitor such ecosystems to stay ahead of the transformations rather than to react to them later.

 

 

 

Hi, I am a Ph.D. student at the National Institute of Oceanography, India. I am currently studying the particulate and dissolved organic matter dynamics in the central and eastern Arabian Sea. I am also interested in the effects of climate change on marine systems, as well as outreach and science communication. My interest in science communication stems from the lack of effective scientific outreach in my country and I wish to contribute to improving that.  In my spare time, I like to read non-fiction and learn about things I didn’t know existed.

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