How do extreme weather conditions affect marine ecosystems? •

Extreme weather events created by human-induced climate change have been on the rise around the world. Droughts, floods and storms often occur in combinations that intensify impacts.

Research on extreme weather events has primarily focused on land-based impacts, and few studies have looked closely at the changes occurring in the largest part of the Earth – the ocean.

In 2011, a heatwave off the coast of Western Australia destroyed biodiversity-rich kelp forests. This is probably the worst known case of a “blob”, a huge bubble of hot water that has formed in the Pacific, killing millions of seabirds, fish and other animals.

A team of scientists led by Professor Nicolas Gruber from ETH Zurich have developed an ocean model to examine this extreme weather event. The researchers concluded that it was not just the high temperatures that caused the mass deaths, but also a combination of events occurring simultaneously.

“When marine life is faced with multiple stressors at once, it struggles to acclimatize,” Professor Gruber said. “For a species of fish that already lives at the upper end of its optimum temperature range, further oxygen deficiency can mean death.”

In an article published in the journal Nature, scientists are calling on other researchers to pay more attention to extreme weather events in the world’s oceans.

“To assess the risks of these types of events, we urgently need to look more closely at the chain of different environmental factors leading to such extremes – and not just in individual regions, but also globally,” said Professor Gruber.

Leading by example, scientists analyzed extreme weather events over the period from 1861 to 2020 and compared them to pre-industrial times. The results showed that the number of warm ocean days increased each year, from an average of four to an average of 40.

While this is an obvious problem, the sad reality is that we know far less about marine ecosystems than we know about the lands we live on. For example, we don’t know the tolerances of many different marine species.

“We know from Swiss forests that beeches are less drought-resistant than, for example, pines,” said Meike Vogt, senior researcher in Gruber’s group.

“We lack a comprehensive understanding of ecosystem structure and function in different ocean regions. Only when we have this basis can we determine the impact of climate change and extremes.

Through Zach Fitzner, Personal editor