Marine heatwaves are harming human health in surprising ways

Marine heatwaves are increasingly being recognized as more than an environmental problem. New research warns that prolonged periods of unusually warm ocean temperatures can also threaten human physical and mental health.

Researchers from Adelaide University and the University of Hong Kong say marine heatwaves should be treated as an important public health concern. They argue that the effects on people have received relatively little attention, even as evidence continues to show how widely these events can affect communities.

The consequences can be severe. The rapid strengthening of Hurricane Otis in 2023 and the destruction it caused in Mexico (an estimated damage bill of more than US$15 billion) have been linked to marine heatwaves. Typhoon Doksuri in 2023, which had impacts across Asia (which affected more than two million people across Asia), has also been associated with unusually warm ocean conditions.

In South Australia, a devastating algal bloom linked to marine heat conditions has also been associated with numerous health problems in coastal communities.

How Marine Heatwaves Can Affect Human Health

A new paper published in Nature Sustainability describes how sustained periods of abnormally high ocean temperatures can set off a chain of consequences for people. These include more severe weather, reduced seafood availability, threats to food safety, disrupted livelihoods and greater mental health pressures in coastal areas.

Lead author Dr. Laura Falkenberg, from Adelaide University's School of Physics, Chemistry and Earth Sciences, said researchers have long recognized the ecological damage caused by marine heatwaves, but their effects on humans have attracted much less attention.

"Marine heatwaves are no longer just recognized as an environmental issue; they are increasingly also perceived as a human health issue," Dr. Falkenberg said.

"Our paper highlights that these events can influence people's health in many different ways, both directly and indirectly. They can intensify storms and atmospheric heatwaves, affect the availability and safety of seafood, disrupt livelihoods and contribute to anxiety, grief and other mental health impacts in communities that depend on healthy oceans."

Marine heatwaves are becoming more frequent, lasting longer and reaching greater intensity as the climate warms. Scientists have already connected them with widespread coral bleaching, large-scale deaths of marine organisms, harmful algal blooms and major disruptions to fisheries and aquaculture.

According to the researchers, those environmental disruptions can have serious consequences for people as well.

Stronger Storms, Unsafe Seafood and Food Security Risks

Extremely warm ocean water can help strengthen weather systems, raising the danger of injuries, deaths and displacement caused by storms and flooding.

Marine heatwaves can also make harmful algal blooms more likely. These blooms can contaminate seafood and create significant health hazards for people who consume or come into contact with affected marine environments.

The effects can continue long after an individual heatwave ends. Falling fish populations and reduced seafood production could undermine food security for billions of people around the world who depend on the ocean as an important source of nutrition.

The Mental Health Toll of a Changing Ocean

The researchers also draw attention to the psychological effects of marine ecosystem loss. People whose livelihoods, traditions and cultural identities are closely tied to the ocean can experience significant emotional stress as familiar environments deteriorate.

In 2025, the toxic algal bloom in South Australia was associated with high levels of 'eco-anxiety,' as well as grief, frustration and depression. The bloom was also linked to physical health problems including respiratory irritation and asthma.

"Many people rely on healthy oceans not only for food and income, but also for recreation, cultural identity and their overall sense of well-being," Dr. Falkenberg said.

"When marine ecosystems suffer, the impacts ripple through communities. We are seeing increasing evidence that these changes can contribute to eco-anxiety, grief and other mental health challenges, particularly for people who feel deeply connected to the marine environment."

Researchers Call for Public Health Planning

The authors say governments and public health agencies should prepare for marine heatwaves in ways similar to how they prepare for heatwaves on land.

That could include using marine heatwave forecasts in public health planning, accounting for human health consequences when making coastal and marine management decisions, and strengthening cooperation among ocean scientists, health agencies and resource managers.

Dr. Falkenberg said preparing before emergencies happen could make communities more resilient as marine heatwaves become increasingly severe.

"Recognizing these health impacts is the first step towards better protecting communities," she said.

"If we only respond after disasters occur, we will continue to experience greater impacts than if we had acted proactively. By understanding the links between ocean health and human health, we can develop better policies that protect both people and the marine ecosystems they depend on."

Reporting from ScienceDaily contributed to this story.