How a marine heatwave transformed life along the Pacific coast

Between 2014 and 2016, something very unsettling happened off the west coast of North America. For over two years, ocean waters from California to Alaska were unusually warm – 3.6°F to 10.8°F hotter than normal. 

This wasn’t a one-off fluke or a seasonal shift. It was the longest and most intense marine heatwave ever recorded in the region.

The heat lingered, spreading across thousands of miles of ocean. This event reshaped life in the water in devastating ways.

Kelp forests collapsed and entire food chains were thrown off balance. Animals appeared in places they had never been spotted before, and many of them died.

An ongoing coastal crisis

The warm water pushed marine life out of their comfort zones – literally. According to newly published research, 240 species were found far beyond their usual ranges during the heatwave, many of them showing up more than 600 miles farther north than normal.

Northern right whale dolphins and small sea slugs like Placida cremoniana were spotted well outside their typical territory. For some species, the shift was temporary. For others, it hinted at a more permanent change. 

As ocean waters heat up, many organisms are following the temperature they’re adapted to – heading toward cooler, northern waters in a bid to survive. But during the historic heatwave in the Pacific, some animals could not move fast enough.

Pacific heatwave unraveled ecosystems

Seagrass beds and kelp forests are critical habitats for fish, invertebrates, and marine mammals. When the kelp disappeared, so did the shelter and food it provided. 

Sea stars, once common along rocky shores, were hit especially hard. A key predator, the sunflower sea star, nearly vanished. Scientists traced the problem to a disease that spread more aggressively in the warmer waters: sea star wasting disease.

Without these predators to keep other populations in check, a domino effect played out across the ecosystem. 

Plankton communities shifted. Forage fish – small species that provide energy to bigger fish, birds, and mammals – declined in number and in nutritional quality. As a result, predators from seabirds to whales had a harder time finding enough to eat.

Many marine mammals experienced unusual mortality events, with entire groups dying off unexpectedly. It wasn’t always clear why – sometimes it was disease or a lack of food, and sometimes it was both.

The impacts rippled ashore

The damage didn’t stop at the water’s edge. When the ocean food web was thrown off, it hit fisheries hard.

Fishers along the Pacific coast saw multiple closures as fish disappeared or disease spread. Entire harvests were lost. 

The economic impact of these changes, including declines in crabbing, salmon, and shellfish industries, added up to hundreds of millions of dollars in losses.

What was once a thriving coastal economy built around marine resources suddenly faced deep uncertainty. Boats stayed docked, and communities that depended on the ocean felt the heat in more ways than one.

A window into future oceans

The study that pulled all of this information together comes from a team of researchers who reviewed 331 published studies and government reports. 

Study lead author Samuel Starko is a former postdoctoral fellow at the University of Victoria. 

“The marine heatwave resulted in unprecedented ecological disturbance across thousands of kilometers of North America’s west coast,” said Starko. 

“Our comprehensive synthesis of the ecological impacts of the heatwave helps us to better understand its overall impacts and how these fit into the broader context of other marine heatwaves.”

Pacific heatwave triggered complex changes

What stood out wasn’t just the number of species affected – it was the complexity of the change. Some impacts were direct. Warm water stressed or killed vulnerable species. 

Other impacts were harder to untangle. One loss led to another, setting off chain reactions that rewrote entire ecosystems.

“As heatwaves become more frequent and intense under climate change, the 2014-16 Northeast Pacific marine heatwave provides a critical example of how climate change is impacting ocean life, and how our future oceans may look,” said Julia Baum, marine ecologist and climate advisor at the University of Victoria.

The authors point to a need for smarter marine conservation efforts that take the whole ecosystem into account. This includes making space for species that are shifting ranges and preparing for the kinds of disease outbreaks that warmer oceans can bring.

The 2014-2016 marine heatwave was not just an anomaly – it was a warning. The results paint a clear picture of how climate-driven ocean warming is already reshaping marine ecosystems.

The study is published in the journal Oceanography and Marine Biology: An Annual Review. 

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