Invasive green crabs linked to decline of shrimp, clam populations

This story originally published at mynorthwest.com

In the serene waters of Willapa Bay, a silent invader is causing a stir among scientists and local communities. The European green crab has been linked to the decline of shrimp, clam and crab populations, posing a threat to biodiversity and local economies.

The green crab is an invasive species notorious for its voracious appetite. In a recent study by the University of Washington (UW) and Washington Sea Grant, it has been found to significantly impact local ecosystems in the Pacific Northwest.

The study examined the diet of green crabs to assess their impact on declining Manila clam harvests.

The research revealed a worrying increase in the abundance and distribution of green crabs in the region, raising alarms for the health of ecosystems. The European green crab is not native to the Pacific Northwest.

More on the species: Invasive European green crab could spell disaster for Washington’s seafood industry

The study made clear immediate action is needed to manage the spread of the European green crab to protect the delicate balance of the Pacific Northwest’s ecosystems and the livelihoods dependent on them. As the green crab continues to feast on native species, the race is on to develop effective management strategies to curb this invasive threat.

These crabs reproduce rapidly. In fact, in some areas, their population doubled in the past year. They damage eelgrass beds, which are crucial for protecting coastlines and reducing carbon dioxide levels in the water.

The study suggests:

“Several ecologically important native species, including the hairy shore crab (H. oregonensis), the Pacific staghorn sculpin (L. armatus), and the sand shrimp (C. franciscorum), are strong candidates for experiencing population-level impacts from increasing green crab populations in Washington State estuaries.”

To understand the impacts of green crabs, researchers examined the stomach contents of green crabs from two different habitats: clam beds and in Willapa Bay. Utilizing DNA methods, scientists have provided an in-depth look at the diet of the European green crab.

The study revealed that green crabs from clam beds had significantly different diets compared to those from intertidal sloughs. A total of 54 unique species were identified from the stomach contents of the green crabs, with the native hairy shore crab being the most common. Notably, two native species, the sand shrimp and the Pacific staghorn sculpin showed the highest DNA abundance in the crabs’ stomachs.

The findings also highlighted the green crab’s preference for certain prey at different sites. For instance, at clam aquaculture beds, the Pacific staghorn sculpin and an invasive amphipod were as commonly consumed as red algae and sand shrimp. In contrast, green crabs at slough sites favored the hairy shore crab, various algae, and a nereid worm.

WA Fish and Wildlife: European green crab continues to cause issues

Despite the green crabs’ presence on Manila clam aquaculture beds, Manila clam DNA was detected in only one crab, suggesting that the impact on clam populations might be less direct than previously thought.

This research not only sheds light on the dietary habits of the European green crab but also demonstrates the potential of DNA metabarcoding as a quantitative tool for analyzing the diets of invasive species. It’s a form of DNA barcoding that allows for the simultaneous identification of multiple species within a single environmental sample.

The future of the region’s biodiversity and aquaculture industries hangs in the balance, making the fight against the European green crab an important topic for environmentalists and policymakers.

Bill Kaczaraba is a content editor at MyNorthwest. You can read his stories here. Follow Bill on X, formerly known as Twitter, here and email him here.

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