By Delcenia Cosman

Homer Independent Press

About two dozen community members, kids and adults alike, dipped their toes into citizen science efforts and joined the Kachemak Bay National Estuarine Research Reserve last Friday to monitor for invasive European green crabs.

The aggressive species eat salmon fry, juvenile native crabs like Dungeness and other fish and decimate eelgrass beds important to fish habitat. Scientists first confirmed them to be in Alaska in 2022 on Annette Island, near the far end of Southeast Alaska. They’ve since continued to spread northward — molted green crab shells were found in Ketchikan last summer.

No green crabs or molts were found on Friday. KBNERR Education Coordinator Ingrid Harrald and Harmful Species Lead Jasmine Maurer checked seven traps set the day before on the east side of the Homer Spit during the afternoon low tide. After recording their findings and walking community participants through the process of identifying, counting and measuring what was contained in the traps, they released several dozen native hairy helmet crabs and a few Pacific staghorn sculpin.

Harrald said that, in addition to trapping, KBNERR searches for crab molts as another method to identify whether the invasive species has hit Homer shores. She asked community members to look for molts while walking along the beach and to try to identify the species that it belonged to.

“That is one way that could be the first way we discover green crabs in our area,” she said. 

Maurer said she set traps on the east side of the Spit, rather than the high-energy west side, because European green crabs prefer lower wave action and “structure” such as that found in the intertidal area on the east. Thick eelgrass beds also are present on the east side of the Spit.

“European green crabs, when they come into an area — when they first arrive — it’s in the high intertidal area,” she said. “That sandy beach (on the west side), they’re never going to hang out there. When I came and set these traps, I put them by rocks, I put them in divots, places like that.

“All these mussel beds that we walked over, all that eelgrass, that is all easy fodder for green crab. They would just eliminate all of that habitat.”

Harrald said that KBNERR used to set traps “at the lowest of low tides,” but as they’ve learned more about the earliest stages of green crab invasion, they’ve changed their habits to match the species’ behavior.

“Green crabs really like the higher intertidal areas. They definitely select for those, especially in early invasion, because the bigger crabs in deeper water will eat them, whereas in the shallow intertidal they’re very, very aggressive, but they can only outdo something that’s the same size as them,” she said.

Continued monitoring will alert KBNERR as to any changes in species present in the bay.

“We can learn about who’s here now ahead of invasion,” Maurer said. “Anything that could happen, we have some information about this place because we’ve been coming here and looking to see who’s already (here), so it’s a good thing to keep doing even though green crab haven’t arrived yet. Then we can monitor for change.”

She noted that, as adults, green crabs are “homebodies” and tend to stay put. In larval form, they mainly move through ocean currents.

“The larva can survive for, like, three months in the current, and you can travel a long way in the coastal current. Most of their expansion in the northeast Pacific has been through larval transport,” Maurer said.

Harrald said that, based on the way tides and currents work in the Cook Inlet and Kachemak Bay, if green crab continue to spread northward from Southeast Alaska, they are more likely to hit coastal communities like Nanwalek or Port Graham first.

“We think that they would be brought into areas on the south side of the bay that are protected and then move their way (up) — but also Kachemak Bay is pretty well connected, so once they’re here, they’re probably going to be everywhere,” Maurer said. “So we have to choose the places that we want to protect from the worst of their impacts and put our effort there.”

She said no state plan current exists to address the green crab invasion.

In the meantime, KBNERR will continue to monitor for green crabs and encourage community participation to spread awareness of the issue.

Learn more about how to participate in community monitoring with KBNERR online.