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Seaweed on Greater Victoria beaches part of largely uncharted ecosystem

Washed-up seaweed feeds insects unknown to any other ecosystem, says RBCM researcher
Clumps of seaweed washing up along the beach off Dallas Road can provide a unique food source to certain types of insects. (Jane Skrypnek/News Staff)

Slimy green sea lettuce and tangles of snake-like bull kelp may feel like a nasty nuisance to Greater Victoria beach goers, but Royal B.C. Museum researchers say they actually serve as a home and buffet for some of the region’s tiniest creatures.

Entomologist Joel Gibson and invertebrate zoologist Henry Choong recently teamed up to explore the largely overlooked ecosystem of washed-up seaweed, known in the research world as “wrack.”

“There’s a whole community there,” Choong said. And it’s an uncommon one at that.

In the ocean, seaweed is a forest-like haven for all kinds of marine life, but when it washes ashore it becomes a food source for very particular types of insects. In fact, Gibson said there are several families of flies he knows of that only feed on bull kelp and don’t exist in any other ecosystems.

“Maybe they’re eating the kelp itself, maybe they’re eating bacteria or fungus growing on the kelp, or maybe they’re eating other insects, but they’re only ever on bull kelp,” Gibson said.

Depending on a single food source is precarious enough when it’s in regular supply, but relying on one as sporadic as washed-up seaweed seems downright dangerous.

“You never know when it’s going to show up,” Gibson said. “It’s like a bus that comes maybe once every six months, but you don’t know what day and it’s the bus you rely on.”

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How the insects manage to survive is one of many questions Gibson and Choong are working to answer. They’re also curious how the ecosystem may differ from beach to beach, where different types of seaweed and algae wash up with various organisms and invertebrates aboard to be fed upon by uniquely evolved insects.

Gibson said records of wrack research go back a hundred years, but it’s only in the last decade or so that scientists have really started looking at it. He and Choong said it’s highlighting the importance of leaving seaweed on the beach.

They’re not against people harvesting some, but said it should never be completely cleared.

“Cleanup can cause a lot of damage to ecosystems,” Choong said. “We have a stake in the well-being of the beach.”

So far, the two have explored beaches around Greater Victoria, up to Port Renfrew, and throughout several islands. Their work will contribute to an ever-growing body of biodiversity research at the Royal B.C. Museum.

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About the Author: Jane Skrypnek

I'm a provincial reporter for Black Press Media after starting as a community reporter in Greater Victoria.
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