The ocean is responding to mounting human threats in surprising waysAlison SnyderIllustration of a pressure gauge with ocean water moving inside...
Published on by Water Network Research, Official research team of The Water Network
Alison Snyder
Illustration of a pressure gauge with ocean water moving inside of it
Illustration: Natalie Peeples/Axios
The stresses of marine heat waves, which are currently at record levels globally, are revealing some parts of the ocean are notably resilient, while others are susceptible to the pressures of a warming world.
Why it matters: The ocean's points of no return, when it can no longer sustain the billions of people it supports, are difficult to determine.
Overfishing, pollution, record-shattering global sea surface temperatures and increasingly common marine heat waves are putting immense pressure on the world's largest ecosystem.
Understanding how marine life can recover — and when it can't — can help prioritize and tailor conservation efforts.
"This is an existential question about human survival on the planet," says Ben Halpern, a marine ecologist at the University of California, Santa Barbara. "Our relationship with the ocean is fragile."
Driving the news: Currently, nearly 50% of the global oceans meet the criteria for a marine heat wave, periods of anomalously warm ocean temperatures that are higher than 90% of the previous observations for a particular date.
This ranks as the most extensive marine heat wave coverage on record for this time of year, dating back to 1991.
These events can profoundly affect marine life, particularly tropical coral reefs, which have a narrow temperature range. When stressed, they expel the symbiotic algae that give them their brilliant colors and allow them to nurture unique fish species, leading to coral bleaching. If exposed to high temperatures for a long duration, they can die.
Marine heat waves can also wreck coastal fisheries, hitting national economies.
The latest NOAA forecast calls for marine heat waves to remain near record level through February 2024, partly as a result of a burgeoning El Niño, combined with long-term climate change.
How it works: Warmer ocean temperatures from heat waves can force fish, whales and other marine life to migrate to cooler waters.
The impact of rising temperatures can be compounded by ocean acidification — a drop in ocean pH as seawater absorbs the ever-increasing amount of carbon dioxide being released into the atmosphere by human activities.
Warmer waters — and pollution — also create low oxygen conditions that increase marine animals' metabolism — but decrease the amount of food available to them, leading to massive fish die-offs.
But it's unclear if marine heatwaves have a universal impact on ecosystems.
Zoom in: A new study of more than 200 marine heat waves that occurred in the oceans around North America and Europe between 1993 and 2019 found more often they didn't have a significant effect on the abundance and diversity of bottom-dwelling fish communities.
SOURCE:https://www.axios.com/2023/08/31/ocean-heat-waves-limits
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