The invasive green crab, scientifically known as Carcinus maenas,
is native to the shores of the northeastern Atlantic Ocean
and the Baltic Sea, ranging from Europe to northern Africa.
The green crab is considered one of the
world's most invasive species.
It has been introduced to various regions through
ballast water from ships, accidental transport, and
intentional introductions for commercial purposes.
Green crabs are relatively small, typically measuring up to 4 inches across their carapace (shell). They have a hexagonal-shaped carapace with five spines on each side called marginal teeth, these are not actual teeth but distinct bumps on the edge of their shell. They also have 3 rostral bumps between their eyes.
Their coloration of their underside can vary from a light yellowish green to a dark burnt orange, but their backs typically have a greenish hue, which gives them their common name. See image to the left.
The impact of green crabs in Maine has been significant and multifaceted, affecting both the state's ecosystems and its economy, particularly the shellfish industry which has already caused significant damage. Here are some of the key impacts of green crabs in Maine:
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Shellfish Industry: One of the most pronounced impacts of green crabs in Maine is on the state's shellfish industry. Green crabs are voracious predators that prey on a variety of shellfish, including soft-shell clams, mussels, and oysters. It’s also believed they prey on juvenile lobster a key industry in the state. This predation can result in reduced populations of commercially valuable shellfish species, leading to economic losses for shellfish harvesters and aquaculture operations. Soft-shell clams, in particular, have been significantly impacted, as green crabs target both juvenile and adult clams, making it difficult for populations to recover.
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Soft-Shell Clam Decline: Green crabs have been implicated in the steep decline of soft-shell clams in Maine. These clams are culturally and economically important to the state, and their decline has far-reaching effects on coastal communities that rely on clam harvesting. The combination of direct predation and disruption of sediment by green crabs has contributed to the decline of this iconic resource.
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Ecological Disruption: Green crabs are invasive predators that can disrupt local marine ecosystems. By feeding on various marine organisms, they can alter the balance of food webs and impact the populations of native species. This disruption can have cascading effects on the health and stability of Maine's coastal ecosystems.
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Marsh Erosion: Green crabs are known to burrow into marshes and sediment, which can contribute to erosion of salt marshes. Marshes play a crucial role in coastal protection, water filtration, and providing habitat for various species. Green crab burrowing can weaken marsh structures and exacerbate erosion, potentially affecting these vital functions.
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Management Costs: The presence of green crabs requires resources for monitoring and management efforts. State agencies, researchers, and stakeholders invest time and funds to study the impacts of green crabs, develop control strategies, and implement management programs. These management costs estimated up to $22 million per year, add to the economic burden of dealing with the invasive species.
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Climate Change Amplification: Warmer waters associated with climate change can accelerate the growth and reproductive rates of green crabs. As Maine's waters warm, it may contribute to the expansion of green crab populations and worsen their impacts.
The impact of green crabs in Maine encompasses economic losses in the shellfish industry, disruption of marine ecosystems, decline of cultural practices, and potential ecological changes. Managing and mitigating these impacts requires a combination of scientific research, monitoring, stakeholder collaboration, and adaptive management strategies.
My objective as a commercial green crab fisherman is to help slow,
if not stop the impact of the green crab on our native marine
ecosystems, by finding as much utility for the crabs as possible and
getting them out of our waters and onto our dinner plates.
You can get a lot of practical information about green crabs from University of New Hampshire's Green Crab Project by downloading their "Green Crab Guide" HERE.