A globe-spanning study published Thursday outlines new, potentially unexpected threats to ocean ecosystems and vulnerable coastal communities within the next five to 10 years that will come on top of the already harmful effects of overfishing, pollution and global warming. 

The goal of what the research team calls a horizon scan is to try to prevent ecological catastrophes. Many of the emerging menaces are linked with global warming, including runoff from areas burned by wildfires, the potentially toxic effects of new biodegradable materials intended to replace plastics, lithium mining from ocean-bottom brine deposits and a rise in toxic metal contamination driven by ocean acidification. 

The research, published in Nature Ecology and Evolution, also warns that many fish will move away from the hottest equatorial ocean regions, leaving a dead zone that diminishes food security for millions of people in developing countries, who rely on fish for daily nutrition. Where fish do remain, global warming appears to reduce their nutritional content because in warmer oceans, plankton produce fewer fatty acids for the fish to consume. 

Omar Defeo, a co-author as well as a coastal ecology and small-scale fisheries researcher at the University of the Republic in Uruguay, said the study’s list of 15 issues “are multidimensional and connected.“

“There are no impacts that have isolated consequences, they work in a cascading way,” he said, “and we will see that this affects already vulnerable communities the most.” 

As an expert in small-scale fisheries, Defeo is no stranger to the interconnected nature of social and environmental issues. He said that, as temperatures rise in oceans, the redistribution of fish species affects fishing communities and food supplies.

“The fish in the tropics will not be able to stay where the temperature surpasses their physical tolerance, changing the species richness in this area,” he said. “This ultimately affects the small-scale fisheries of the tropics where there is already social inequity. So now we see economic, social and nutritional issues arise for these communities.”  

Defeo said that, without more of a global effort to introduce policies that slow the impacts of these emerging issues, countries susceptible to environmental and economic volatility will have to bear the largest burden. 

Understanding and highlighting the new threats helps guide monitoring and policies to protect marine and coastal environments, said co-author Ann Thornton, a biologist at the University of Cambridge. Similar global scans have been conducted since 2009, she added, but this is the first focusing solely on marine and coastal issues. 

The 2009 scan identified ocean plastic pollution as an emerging threat that quickly became a runaway global crisis driving an emergency response, but long after significant damage had been done to marine ecosystems. Taking the warning to heart 20 years ago could have prevented some of those impacts, she said.

The research team included 30 experts from 11 countries who joined forces to identify emerging changes to marine and coastal habitats. Using a method known as horizon scanning, scientists submitted a total of 75 new ocean issues just appearing on the science radar. 

The entire team, made up of marine and coastal scientists, practitioners, and policymakers narrowed and divided the list of issues through several rounds of reading and voting into three main categories: ecosystem impacts, resource exploitation and novel technologies. 

Through that process, the researchers realized that it would take 10 to 15 years before they fully understand “whether or not these issues are going to come to provenance,” Thornton said. “We feel it gives the opportunity for policymakers and practitioners to at least have a think and say, ‘Hang on, we haven’t thought of that.’”

Mark Spalding, a senior marine scientist with The Nature Conservancy, said the focus on soft robotics could be valuable.

“The idea of robot swarms heading to map ocean habitats is intriguing,” he said. Given that right now we have basically no idea of what’s on the seabed below the depths that satellites can see, about 10 to 30 meters, such mapping is urgent.

The new study’s call to focus research on extraction of marine collagens, used for health products, is “surely a good example of where stepping in, in a timely manner, could be quite powerful to steer a potentially important production in a sustainable fashion,” he said. “Done right, it could be a highly effective use of fish waste.” 

A Deep Sea Carbon Pump

For example, the projected increase of large-scale harvesting of mesopelagic fish living between 200 and 1,000 meters deep in the ocean, could provide an option for increased nutrition and food supply in a time of global food insecurity, Thornton said.

“But the underlying issue is that we don’t know the contribution these species make to carbon sequestration,” she said. “That’s only coming to the fore, so before we start taking these species from this depth, we need to stop and say, ‘Hang on a minute, what are the wider consequences on the ecosystem and on our overall ability to reduce carbon in the atmosphere?”

Recent research suggests those fish function as “a huge carbon sequestration pump,” she said. “That was previously not acknowledged simply because nobody has researched it.” 

The mesopelagic species usually lurk on the deep ocean floor using bioluminescent lures and other baubles to catch prey, but the new research cited in the horizon scan suggest they make what is believed to be the longest daily vertical migration of any fish species to feed on plankton at the surface.

“I really got quite excited about this because these are bug-ugly fish with the spotlights, the lanterns, the angler fish. I just think they’re utterly fascinating,” Thornton said.

With better surveys, researchers are realizing how much of the ocean biomass is contained in these species, with high densities detected in places like the Arabian Sea, the Mediterranean and the North Atlantic. The densities appear to lower in the southern oceans, but that could also be just because the sampling area is so vast that they have yet to be accurately counted, she added.

When the mesopelagic fish come up to the surface to feed, “they take the carbon in the phytoplankton and algae they eat, and, defecating at depth, the carbon sinks to the ocean floor and gets sequestered,” Thornton said. By ingesting the surface species, they’re ingesting calcium carbonate, “which, to be blunt, makes their poo heavier so it sinks.” But their role in storing carbon at the ocean bottom is only emerging because scientists “didn’t appreciate the sheer numbers and biomass of these species,” she said.

“You can get these situations where it’s jaw-dropping, and you think my goodness, we’ve never thought of that,” she said. “All of the 15 issues we identified have resulted in the majority of the people on the panel having that jaw-dropping moment.”

The newfound understanding of the importance of deep sea fish populations also shows how deep-ocean research is lagging in comparison to biodiversity research on land, partly because it’s technically difficult and expensive, and partly because of the sheer size of the ocean, she said.

“We simply don’t know what the benefits are from these lithium pools, from the deep sea, in terms of planetary regulation,” Thornton said. “They must be doing something. We don’t yet know what services are being provided by the deep sea, and we’re just going in and starting to exploit it.”

Even though the initial scientific canvassing didn’t include specific questions about climate, global warming emerged as a common theme linking many of the issues identified, said co-author James Herbert-Read, a biologist at the University of Cambridge.

“That really highlights that climate change is the biggest issue facing biodiversity,” he said. But there are other lesser-known impacts to oceans, he said, that will eventuate from climate change. These include increasing wildfires; coastal darkening, or a reduction in the amount of light that penetrates upper ocean layers, and even increased pollution by toxic heavy metals mobilized by rising ocean acidity. 

Laundry List of Impacts

The growing demand for lithium used in renewable energy technology like batteries is another one of the key potential threats to ocean biodiversity. Herbert-Read said lithium in deep sea brine pools with high salt concentrations could become attractive targets for extraction, but recent deep sea surveys showed they may support a surprising amount of marine life.

“If we don’t look at what is there, and understand what diversity of life we have there, and we go extracting from these places, we don’t know what we’re losing. Let’s make sure we don’t lose things we didn’t even know we had,” he said.

Irene Schloss, co-author and biological oceanographer from the Argentinian Antarctic Institute, echoed Herbert-Reed’s message about lithium and its unintended consequences.

“On the lithium issue, it’s fantastic to have electric cars, but it’s known that the lithium mining can perturb the ocean, it can perturb the fauna,” she said, “we have to think of every single step and up to the last drop of the ocean, if it has any consequence.” 

The study also shows how panicked emergency policy and market responses to environmental crises can simply trigger another problem if the policy is not well thought out, Herbert-Read said. That includes replacing fossil fuel-based plastic with so-called biodegradable plastic made from plant-based starches.

The problem is that those materials don’t really biodegrade under natural conditions, he said. They’re designed to be degraded in yet another industrial process, and as these materials meant to replace plastic reach the ocean, they are causing a new round of problems. 

There have only been about a dozen eco-toxicological studies done on the effects of those materials, with half of the studies suggesting they are harmful to ocean life. He said they can contain chemicals as toxic as those found in conventional plastics, and some of the study results show that they can reduce species abundance and richness, decrease growth rates in fishes and disrupt organisms’ physiology. Even less is known about their long-term effects.

“There is a big push for these materials as part of the circular economy, but we don’t want to be pushing something if we don’t understand the negative effects,” he said.

Another example of unintended consequences in response to environmental challenges can be seen through the advancement of technology such as soft robotics, underwater tracking systems, or even floating marine cities—all included on the list.

“Technology is important, but if it is not supported by a development plan and without plans of management and governance, technology alone will not provide solutions for the future,” said Defeo. 

Coastal Darkening

Many different types of human impacts combine to cause coastal darkening, which affects plankton, at the base of the ocean food chain, as well as algae, kelp and seagrass, which play an important role in pulling carbon dioxide into the ocean.

“Increased precipitation, storms, permafrost thawing, and coastal erosion have led to the ‘browning’ of freshwater ecosystems by elevated organic carbon, iron, and particles, all of which are eventually discharged into the ocean,” the scientists wrote. 

Increasing wildfires are also a factor because when rain washes soil off burned areas, it contributes to coastal darkening. And when soot particles from wildfires reach the ocean, it can also lead to more prolific growth of algae and plankton.

Such changes affect ocean chemistry, including photochemical degradation of dissolved organic carbon and generation of toxic chemicals. The combined effects could profoundly alter ocean ecosystems, shifting the mix, distribution and behavior of species in affected areas, along with degrading coastal habitats and their ecological functions, including carbon sequestration. 

While intense and large-scale coastal darkening will likely harm ocean ecosystems, the same phenomenon, at more moderate levels, could also “have some positive impacts such as limiting coral bleaching on shallow reefs,” the authors wrote.

Schloss said she would like people to see the study not only as a step forward, “but a step that has to continue, a step through a long walk.”

Although he finds it difficult to be optimistic, Defeo does believe something positive can come out of this study. “The positivity will be measured by the management of all the issues listed,” he said, “There can be a positive outcome, but it will depend on all of us.”