Invasion of the Green Crabs!

Since I was away on vacation, there have been many things going on that have implications for both the economy and the environment in Maine. As it turns out, the very area where I and my family were camping is actually Ground Zero for one of the most potentially important invasions in Maine’s local history: the green crab.

The green crab, of course, is not new to Maine waters. According to a lecture I attended at the Gulf of Maine Institute, given by Professor Brian Beal of the University of Maine at Machias, green crabs first arrived in Maine in the holds of boats from northern Europe. But a combination of events has made the green crab, in Professor Beal’s words,”the consummate invader of new ecosystems.”

Their first weapon? Incredible fecundity. Again, according to Professor Beal, a small  (two inch) female green crab can lay as many as 165,000 eggs at a time. That’s a lot of eggs! And a larger female can lay more eggs than that. The females reach sexual maturity at 2 or 3 years, and they typically live for up to 6 years.  Doing some simple math, then, the average female could lay up to 660, 000 eggs in her lifetime.

Their second weapon is resilience. The larvae have an incredible tolerance for a wide range of temperature and salinity , meaning that they can survive conditions that might have killed other, less hardy species.

Third weapon? Voraciousness. These things eat virtually anything. And I mean anything. Most concerning, from an economic viewpoint, is their effect on the soft shell clam industry. One green crab can eat up to 40 soft shell clams a day. That’s a lot of clams! They also have been known to eat lobster larvae and baby lobster, and compete with them (and win) for food sources as well.

In addition, green crabs can wreak devastation on eelgrass beds as they burrow into banks along the edges of tidal flats. The destruction of the eelgrass has two negative effects: erosion of the banks surrounding tidal flats, and removal of habitat for juvenile fish.

Given that the soft shell clam industry in Maine brings in $15 million a year, and given that an estimated 1,700 soft shell clam harvesters rely on the critters for their livelihood, that’s a huge impact. Add to that the effect on the lobster industry (no need to tell you how big that is in Maine), and you have the makings of an economic catastrophe, not just an ecological one.

Do I exagerrate? Possibly. After that very harsh winter we endured in Maine, it’s possible that the green crab population will not be quite so robust this year. However, there is some evidence that climate change may be responsible, in part, for the warmer waters that prove so hospitable to the invasive species. If that’s the case, then we can expect fewer cold winters like the one we just went through to keep the green crab population in check. We may have gotten a respite this year. We should take it to research methods of either protecting the soft shell clam industry from the invaders, replanting eelgrass in protected areas, finding a way of reducing the green crab population so that it doesn’t rebound again) or a combination of the three. Creating a demand for the green crabs – either as food for humans or as lobster bait – may go some way towards alleviating the damage. But the invisible hand of the market can only go so far in this case.