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New EU-project: Linking marine habitat status to predators

Collage of three photos. One man smiling to the camera, wolf fish on the sea floor and sea urchin.

IMR researcher Even Moland and colleagues from several countries will look further into loss of predators in marine ecosystems, such as wolffish. One such consequence is overgrazing of kelp by sea urchins.

Fishing drives a reduction in the number of large and old predatory fish. What does this mean for ecosystems?

“We know that many coastal ecosystems are under strong pressure, also in northern Europe”, says researcher Even Moland at the Institute of Marine Research (IMR).

“An example of a region where we find marine habitats in poor status is the Kattegat and Skagerrak Seas”. 

Fishing affects the habitats of fish and other marine animals

The status of marine habitats in Europe and elsewhere is tightly linked to fisheries. 

“Fishing has direct physical impact on marine ecosystems and habitats – for example caused by bottom trawling – but importantly also via indirect effects” explains Moland.

One of those indirect effects is now at the centre of a new EU-funded project that Moland and IMR will lead over the next four years, MARHAB.

“It is all about the loss of the large and functionally important marine predators.”

What are the consequences when the predators are fished away? 

An ecosystem is a story about how “everything is connected”. One might also talk about the “story of who eats who”. 

As on land, we find both "grass" and grazers that eat grass, and larger animals that eat the smaller ones in the sea.

And as we may remember from biology class: there are fewer of the large predators at the top of the pyramid than there are nearer the grass at the bottom.

But when we fish, we prefer to catch the big fish, because that's what we want for dinner.

“When we remove a large part of the larger, older predatory fish, it creates ripple effects through the ecosystem. In scientific terms, we call such ripple effects trophic cascades. We need to find ways to buffer such cascades through management of both nature and fisheries” Moland says. 

“An example of a trophic cascade is the formation of so-called urchin barrens. When the predators that should have controlled the sea urchin populations have been removed, urchins thrive. Unchecked by predators they are capable of grazing down entire kelp forests and the seascape is transformed into a barren instead of a productive and high-diversity kelp forest.” 

sea ​​urchin on the sea floor
When no one is eating sea urchins, there will quickly be a bit too many of them. Image: Erling Svensen/IMR 

Aiming to improve the status and management of marine habitats

The goal of the EU project is to better understand the consequences of fewer predators in ecosystems and find good strategies to incorporate function into conservation and fisheries management.

Future fisheries management should include strategies to ensure that enough of the large and old predatory fish are present to keep the system "in check" – as such function is sorely needed under climate change.

a figure showing a cycle with different working methodics the project will use

“We want to combine important knowledge from area-based conservation of biodiversity with traditional fisheries management. The MARHAB project will demonstrate how the goals of the two approaches can be coordinated and how fisheries management can also preserve the large individuals and functionally important predatory fish”. 

The Kattegat-Skagerrak region will be a case study area for the four-year project.

“These questions are also highly relevant beyond this region, and the project will be transferable to other regions and countries both within and outside the EU," Moland concludes.