Green crabs first arrived in North America in the 1800s through merchant ships traveling from Europe. They are considered one of the most invasive marine species, preying on salmon, juvenile king crab, and other shellfish. Fortunately, the green crab has not yet been found in Kachemak Bay.
In 2022, the first signs that European green crabs had reached Alaska were found on the beaches of Annette Island. Now, organizations like the Kachemak Bay National Estuarine Research Reserve are actively monitoring green crab populations. Their efforts include regular beach surveys, trapping programs, and community involvement to help identify and manage the spread of this invasive species.
Jasmine Maurer is the Harmful Species Program Coordinator at KBNERR. She said Alaska’s scientific communities, along with commercial fisheries, are concerned about the potential impacts the crabs could have on the ecosystem.
“That ability to dig and change the physical environment through their burrowing, adding to erosion and sloughing off of soft banks, as well as destroying eelgrass beds that are so important for nursery habitat for a wide range of forage fish, of juvenile salmon... shorebirds also forage in eelgrass beds,” Maurer said.
Maurer said European green crabs can survive in temperatures ranging from freezing up to 86 degrees Fahrenheit. They can also tolerate a range of salinities, allowing them to move up estuary systems where saltwater mixes with freshwater, further extending their potential reach.
KBNERR’s early detection trapping efforts involve using baited traps to attract crabs for analysis. The collected crabs are measured and categorized, providing a way to detect green crabs before they become established in the area. While green crabs haven't reached Kachemak Bay yet, Maurer said monitoring provides important information that will be compared with data collected from other areas around the state.
“There is quite a long list of partners throughout the state that are doing this effort. We use a set style of trap and methods so that we can compare data and have an understanding of how the invasion is progressing and compare what is going on in our natural environments ahead of invasion as well. So it gives us good baseline data,” Maurer said.
Maurer said there are a few different ways communities can get involved in monitoring for the invasive European green crab.
“You can come and volunteer at a discovery lab, you can come out and help crab trap. If you have a beach that you are particularly fond of and want to do a molt walk, we can make sure you have the datasheet to do that. Again, it's a way to be looking for what's there early,” Maurer said.
You can identify a European green crab by looking for the five spines behind each eye on both sides of the shell. Report molted shells or live green crabs to the Alaska Department of Fish and Game.
