Nova Scotia

Invasive green crab impact being surveyed by conservation group

The Nature Conservancy of Canada will be using a drone, chartered aircraft, as well as "boots on the ground," to try and get a clearer picture of the impact of the invasive green crab on eel grass beds.

Green crabs destroy ecologically vital eel grass as they feed their voracious appetites

Alien green crab, which likely originated in the Mediterranean, were first introduced to New Jersey in 1817. By the 1950s, green crab had found their way north to waters off southern Nova Scotia. (CBC)

The Nature Conservancy of Canada will be using a drone, chartered aircraft taking aerial photographs, as well as "boots on the ground," to try and get a clearer picture of the impact of the invasive green crab on eel grass beds.

European green crab have been eating their way up the coast, feeding on clams, oysters, mussels, small fish — but perhaps most alarming is their tendency to destroy ecologically vital eel grass in the process.

Eel grass serves as a nursery for many important commercial marine species, as well as for a number of species at risk. Without the eel grass, these lush estuaries become underwater deserts and that can have a huge impact on species that rely on it.

"It's an important part of the chain. It's a food source to many animals. It's also habitat for crustaceans, invertebrates and those are the kinds of things other creatures feed on," said Doug van Hemessen, stewardship coordinator for the NCC. 

Eel grass meadows are also important for filtering and trapping sediment, improving water quality and helping sustain migratory waterfowl, according to the NCC.

The conservancy hopes the survey of more than 445 hectares of the Pugwash River Estuary will give conservationists a better idea of the amount and the health of eel grass beds in the area.

Without the eel grass, lush estuaries become underwater deserts and that can have a huge impact on species that rely on it. (dfo-mpo.gc.ca)

Craig Smith, program manager for the Nature Conservancy of Canada, said the project is designed to help track how eel grass is surviving against an "increasing and significant threat."

"Eel-grass meadows are one of the most productive ecosystems in the world," said Smith.

"Their slippery, grass like leaves provide numerous benefits to coastal environments and we are creating a baseline dataset of eel-grass in the estuary to help detect future changes."

Van Hemessen  saids the other part of the study is to create and nurture a market for the green crab so that people will be encouraged to trap them.

"It's something that will never be entirely gone, it's here to stay. But if we can manage the numbers, the eel grass will respond favourably in turn," he said.

Alien green crab, which likely originated in the Mediterranean, were first introduced to New Jersey in 1817. By the 1950s, green crab had found their way north to waters off southern Nova Scotia.

In recent years, they have rapidly expanded their range around Cape Breton, north to Prince Edward Island the Magdalen Islands of Quebec and into even colder waters around Newfoundland.

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