Many species of fish we commonly eat have a crucial role in keeping the seabed, according to a study published in Marine Environmental Research. The authors suggest that affecting these species will significantly impact our climate.
Researchers at the Convex Seascape Survey assessed how some fish are involved in churning and moving sediments on the seabed (a process called bioturbation) in shallow UK waters. This involves, for example, fish that excavate sediment during foraging or build nests in the sand. These different ways of reworking the sediments and frequency were used to calculate a bioturbation impact score for each species.
Results showed that the Atlantic cod (commonly eaten worldwide) topped the list of these critical species, along with Atlantic hagfish and European eel. In total, the authors list 185 fish species that play a role in bioturbation, and 120 of these are targeted by commercial fishing.
“Ocean sediments are the world’s largest reservoir of organic carbon – so what happens on the seabed matters for our climate. 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,” said Mara Fischer from the University of Exeter. “Bioturbation is also important for seabed and wider ocean ecosystems. We have a good understanding of how invertebrates contribute to global bioturbation – but until now, we have been missing half the story. Our study is the first to attempt to quantify the bioturbation impact of fish, and it shows they play a significant, widespread role.”
Worryingly, species with the highest bioturbation impacts are also among the most vulnerable to threats such as commercial fishing. “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. These losses translate into big, but still uncertain, changes in the way seabed ecosystems work,” said Professor Callum Roberts from the Centre for Ecology and Conservation at Exeter’s Penryn Campus in Cornwall.
Examples of species involved in bioturbation include:
- European eel: These fish can burrow. They are considered a delicacy in many parts of Europe and Asia and are fished primarily using traps and fyke nets.
- Atlantic cod: These fish are classed as vertical excavators. Typically fished using trawling, they are consumed in many forms, including fish and chips, fresh fillets, salted cod, and cod liver oil. Populations have declined in several parts of its range, particularly the North Sea and West Atlantic.
- Common skate: These fish are known as lateral excavators. Historically targeted by trawling, this species is now protected in several regions and is often caught accidentally. However, its numbers have drastically declined due to overfishing.
- Black seabream: These fish can build nests in the sand. They are primarily caught using bottom trawling and hook and line. Fishing during the spawning season in April and May can impact population replenishment, and bottom trawling at this time has the potential to remove the fish, nests, and eggs.
- Red gurnard: These fish can move sediment at the bottom of the sea. Historically not of major commercial interest, the species has been targeted more in recent years. There is currently no management for any gurnard species in the EU, which could lead to unsustainable fishing.
“Anyone who has spent time underwater, whether snorkelling or diving, knows that fish are constantly digging up the seabed. It’s hard to believe that such an obvious and important activity has been largely overlooked when it comes to understanding ocean carbon burial,” concluded Julie Hawkins, also from the University of Exeter:
Fischer M, Lewis CN, Hawkins JP, Roberts CM. A functional assessment of fish as bioturbators and their vulnerability to local extinction. Mar Environ Res. 2025 Apr 17:107158. doi: 10.1016/j.marenvres.2025.107158.