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February 16, 2016

Tiny, But Vital, Builders of Muddy Bottom Habitats Are Vanishing

Now dominated by tube worms and brittle stars, this mud bottom was once inhabited by haploops crustaceans. Haploops are disappearing in sites around Europe, and scientists aren't entirely sure why.


Stately kelp forests and rainbow-colored coral reefs are known for the amazing amount of life that calls these habitats home. But don’t count out the muddy seafloor, especially if it harbors a tiny crustacean called a haploops. These animals, related to the sandhoppers often found on beaches, build small mud tunnel homes that litter the ocean floor. While they might not win any beauty contests, these “communities” of thousands of haploops form critical habitat for scores of species across northern Europe’s oceans. But they’re in danger of disappearing unless governments take steps to protect them.

The four tube-building species of Haploops amphipods cement their mud homes with “amphipod silk.” Clusters of these animals form vital feeding grounds and nurseries for sea urchins, brittle stars, tube worms and commercially important flatfish such as plaice and halibut.

The dense, muddy bottom communities that haploops construct are vanishing — and scientists aren’t entirely sure why. In one area off the coast of Sweden, for example, haploops went from abundant to almost nonexistent in just ten years. The current distribution of these tiny crustaceans may only be 10 percent of their historical range.

Their decline may be related to bottom trawling, a fishing method that drags nets along the seafloor to scoop up bottom-dwelling fish, damaging delicate structures like haploops tubes in the process. This destructive fishing method is often likened to clear-cutting forests, and it can take years for marine ecosystems to recover.

In the narrow Øresund Strait, which separates Denmark from Sweden, a decades-long ban on bottom trawling has helped to preserve haploops communities, along with other rare habitats including horse mussel beds and methane seeps that support diverse animal and algal communities.

Despite being one of the busiest shipping routes in the world, the health of the Øresund Strait’s bottom habitats supports unusually plentiful fish stocks, says Hanna Paulomäki, Oceana’s Baltic Sea project manager.

Nonetheless, haploops are on a downward trend even in Øresund Strait. The area is bordered by densely populated cities and industrial zones including Copenhagen in Denmark and Malmö in Sweden. These regions produce pollution and excessive levels of nutrients that damage marine life. Dredging — which scoops sand from the seafloor along with whatever else lives on top of it — remains legal outside of a few protected areas.

Recently, environmental advocates called upon the Danish and Swedish governments to declare the entirety of Øresund a protected area, uniting the scattered protected zones under a single management plan. As Paulomäki explains, a coherent management strategy is the best way to safeguard haploops and other rare seafloor communities from the catalog of threats that affect them. 

Beyond the Øresund straight, things are looking worse for the haploops. In January, European countries bordering the Northeastern Atlantic declined to expand protections for threatened marine species and habitats in the region, ignoring scientists’ specific recommendations to protect haploops communities and kelp forests.

Oceana works in Europe and around the world to protect threatened habitats in order to foster marine biodiversity and increase fish stocks. Learn more about our campaigns to preserve unique marine ecosystems in Europe and protect the Baltic Sea, or support our work through a donation.