The uneven impact of marine heatwaves on ocean’s apex predators

Marine heatwaves may shrink the habitats of some large ocean predators to next to nothing, while other hunters of the sea may see an increase in their ranges according to new research.

Researchers from the US National Oceanic and Atmospheric Administration (NOAA) have modelled the impact of 4 recent marine heatwaves in the Northeast Pacific on apex predators. The 14 species on which the study focuses include sharks, whales, seals, seabirds, tuna and turtles.

Turtle surfaces for air with tag on its back
A tagged female leatherback turtle takes a breath in Monterey Bay during 2016. Credit: Kate Cummings, Blue Ocean Whale Watch.

Their results are published in Nature Communications.

It is believed the findings will help in understanding the varied responses of marine predators to heatwaves and in developing tools to predict their distributions in near real time, to aid conservation efforts.

Marine heatwaves are short-term extreme warming events. They can have major impacts on ecosystems as well as on humans, such as increased moisture in the atmosphere leading to unusual weather events like Tropical Storm Hilary in California.

Last week, oceanographers predicted that a patch of the Tasman Sea off the coast of Australia is expected to experience “off-the-scale” temperatures of at least 2.5°C above average in a marine heatwave expected between September and February. That event is expected to have damaging impacts on Tasmania’s already reeling giant kelp forests which are a critical marine ecosystem in the region.

While previous studies have examined the long-term effects of climate change on marine species, less is known about how short-term intense events like marine heatwaves impact on ocean-dwelling creatures.

The authors of the new study looked at heatwaves in 2014, 2015, 2019 and 2020 that impacted parts of the Northeast Pacific Ocean.

Responses varied between the different species but were predictable.

Some species experienced near-complete habitat loss. This included the 2015 habitat shrinkage of bluefin tuna and blue sharks. However, others saw habitat gain. California sea lions and elephant seals experienced a near two-fold habitat gain in 2019.

“The variability in predicted responses across species and heatwaves portends the need for novel management solutions that can rapidly respond to extreme climate events,” the authors write.

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