It isn’t too often that I get excited to see something dead on the shoreline, but this is true for green crabs. It was true for the first one I saw this season, but sadly not those I’ve spotted since. The past several cold winters have been good for keeping the population of these invasive crabs in check, but this past mild one has had people worrying. Reports of green crab sightings have been increasing along the coast this spring.

Green crabs are not native to Maine and have wreaked havoc on the ecosystem by multiplying like crazy and nibbling away at all of the precious eelgrass that provides protection for lots of little critters along with supplying the water with a fresh supply of oxygen. They’ve also decimated the clam population in the past, crunching through the shells of these valuable species. Perhaps that’s why they are called Carcinus maenus – because they are so mean! Green crabs are native to Europe and first showed up in Casco Bay in 1900 or so. The most recent peak in their population was in 2012. That’s when they caused visible damage to eelgrass and shellfish beds along the shore. Since then, however, those resources have started to recover and that’s why it is worrisome to see them making a come back.

A lot of work has gone into trying to get rid of these crabs. Various groups have placed traps along the intertidal to remove them. These range from municipalities to non-profits like the Quahog Bay Conservancy (QBC) in Harpswell. According to one of QBC’s Summer Interns, Destiny Belanger, “We have been seeing A LOT of them this year. Last year, our total was about 9,000 individual crabs. This season we are already at about 6,500 and our season has just started.”

Once they’ve been trapped, what do you do with them? Some have been used for bait and some turned into fertilizer. Others are being tested for use in various creative recipes. They apparently possess an “umami”-like flavor-boosting quality that makes them good for broths and as food additives. In Georgetown, there is even a nascent soft-shell crab fishery developing, following in the tradition of a similar traditional fishery in Venice, Italy.

Aside from trapping them, another helpful thing to do is to collect information on where they are being found. This is something that anyone can participate in once they learn to identify green crabs. It may seem simple at first – look for a crab that looks green, but despite their name, they aren’t always green. The easiest way to identify them is to look at the number of spines on each side of their shell. Green crabs have five of these between their eyes and the widest part of their shell. They also have three roundish bumps between their eyes and a shell that is shaped like a pentagon.

There are several other species of crabs around here – some native and others invasive. The most common native shore crab is the rock crab (Cancer irroratus), also known as peekytoe crab. They are reddish-orange in color and have nine spines on either side of the top edge of their shell, three spines between their eyes, and an oval-shaped shell. One other common invasive species is the Asian shore crab (Hemigrapsus sanguineus). These can also be green, but can also be purplish or orangey-red. They have three spines on either side of their shell. They other telltale identifier are the light and dark bands along their legs and red-spotted claws.

If you find invasive crabs, there are a few places to report your findings. For locations all across the state, you can report them to the Maine Department of Marine Resources (DMR) ([email protected]). More locally, Friends of Casco Bay is collecting information for the Bay ([email protected]), and even more locally, if you find them in Brunswick, you can contact the town’s Office of Coastal Resources ([email protected]). Or, if you find them in Harpswell, you can email the Quahog Bay Conservancy ([email protected]).

Hopefully, this is just a spring spike in the green crab population that people are seeing and it won’t turn into a large problem. The efforts of citizen scientists including anyone making observations along the coast can make a big difference to resource managers and non-profits in their ability to deal with invasive species. Learning more about them and how to identify them is a good first step to helping out

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