Fish are quietly battling climate change on the seabed

When we think of climate heroes, fish might not be the first thing that comes to mind. Yet many of the species we commonly eat are doing more than just swimming around – they’re busy reshaping the ocean floor.

This quiet activity, known as bioturbation, turns out to be a major player in the process of storing carbon beneath the seabed.

In a recent study from the University of Exeter, scientists examined how fish contribute to bioturbation in shallow waters around the U.K.

The research focused on the critical role fish play in mixing ocean sediments and what that means for both the health of marine ecosystems and our changing climate.

How fish slow climate change

The researchers found that 185 fish species actively help churn and rework the seabed. Of those, 120 are regularly caught by commercial fisheries.

Some of the most active species include Atlantic cod, Atlantic hagfish, and European eel, which are all well-known names in fish markets and kitchens. These fish aren’t just food. They’re key to maintaining the seabed’s ability to store organic carbon.

“Ocean sediments are the world’s largest reservoir of organic carbon – so what happens on the seabed matters for our climate,” said University of Exeter Ph.D. student Mara Fischer, who led the study.

“Bioturbation is very important for how the seabed takes up and stores organic carbon, so the process is vital to our understanding of how the ocean absorbs greenhouse gases to slow the rate of climate change,” she added.

Fish modify ecosystems

The process of churning and mixing the seabed sediments results in changes to the physical and chemical characteristics of the substrate. It is essentially a form of modifying the ecosystem through burrowing, feeding, digging and disturbing the deposits on the bottom.

Bioturbation is important for the wider ocean ecosystems, as well as for the sediments on the sea floor.

“We have a good understanding of how invertebrates contribute to global bioturbation – but until now, we have been missing half the story,” explained Fischer. “Our study is the first to attempt to quantify the bioturbation impact of fish, and it shows they play a significant, widespread role.”

Overfishing threatens key fish species

Many of the fish that do the heaviest lifting on the seabed are facing serious threats because they are popular eating fish.

Professor Callum Roberts is an expert in the Center for Ecology and Conservation at Exeter’s Penryn Campus in Cornwall.

“Many of the largest and most powerful diggers and disturbers of seabed sediments, like giant skates, halibut and cod, have been so overfished they have all but vanished from our seas,” said Professor Roberts.

“These losses translate into big, but still uncertain, changes in the way seabed ecosystems work.”

Measuring the contribution of fish

To measure each fish’s contribution, the team looked at three factors: how the fish rework sediment (called their bioturbation mode), how often they do it, and their body size. This helped them calculate a “bioturbation impact score” for each species.

European eel

The European eel is a burrower, with a bioturbation score of 100 out of 125. It is listed as critically endangered. It is mainly fished using traps and nets and is considered a delicacy in many places.

However, it faces several threats, including pollution, habitat loss, diseases, parasites, and climate change.

Atlantic cod

The Atlantic cod, which excavates vertically, also scored 100. It is listed as vulnerable and is caught primarily through trawling and longlining. It is widely consumed in dishes such as fish-and-chips, salted cod, and fresh filets.

Overfishing, climate change, and habitat degradation have led to significant population declines, especially in the North Sea and West Atlantic.

Common skate

The common skate is classified as a lateral excavator and has a bioturbation score of 50. It is critically endangered. Although now protected in some areas, it is often caught accidentally as bycatch.

Common skate numbers have plummeted due to overfishing. The species is particularly vulnerable because of its large size, slow growth, and low reproductive rate – each female lays about 40 eggs every other year, and it takes 11 years to reach maturity.

Black seabram

The black seabream is a nest builder with a bioturbation score of 36. It is listed as a species of least concern. It is primarily caught using bottom trawling, gillnets, and hook-and-line. Fishing during the spawning season in April and May can disrupt nest building and reduce population growth. Bottom trawling at this time can destroy nests and remove both fish and eggs.

Gurnard fish species

The red gurnard, a sediment sifter, scored 16. It is also listed as being of least concern. While historically not a major target for commercial fisheries, the red gurnard has become more commonly fished in recent years, including in Cornwall. It is mainly caught by trawlers.

There are currently no fishing regulations for gurnard species in the E.U. – no minimum landing size, no quota – raising concerns about sustainability.

Fish support seabed health

It’s surprising how long this important role of fish has gone unnoticed. “Anyone who has spent time underwater, whether snorkeling or diving, knows that fish are constantly digging up the seabed,” said study co-author Julie Hawkins.

“It’s hard to believe that such an obvious and important activity has been largely overlooked when it comes to understanding ocean carbon burial.”

The research was part of the Convex Seascape Survey, a five-year global project led by the University of Exeter, Blue Marine Foundation, and Convex Group Limited.

The survey is the largest of its kind aimed at learning how oceans and continental shelves fit into Earth’s carbon puzzle.

Understanding how fish support seabed health could help shape future conservation and fishing policies. As climate change accelerates, every part of the system matters – and fish may be doing more for us than we ever imagined.

The full study was published in the journal Marine Environmental Research.

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