European green crabs invade Alaska
In the documentary series Alien invasion: are we ready? (now streaming on Peacock!) Scientists and military specialists imagine what a real alien invasion might look like. Ever since the idea of potential extraterrestrial intelligence caught on, we’ve been quietly obsessed with thinking about how events might unfold and what, if anything, we might do to stop an invasion. Countless books, movies, and video games explore the question, and the genre probably isn’t going away.
While we had our eyes on the sky, however, we experienced a slower, more mundane invasion here on the ground. Or, more precisely, in the water. Over the past two centuries, a growing army of European green crabs has slowly made its way across North America and it seems they are marching on a new front. They are well equipped too. Crabs seem to be nature’s favorite form. By invasion or evolution, we are all destined to be crabs one day…maybe.
European green crabs first appeared in America about 200 years ago, probably as a result of colonization. For most of the elapsed time, they have been largely isolated on the East Coast. Large tracts of land are not the typical meeting places for most crabs, so our Pacific coasts were safe. Or so we thought. But like the elves of Middle-earth, the green crabs always had their piercing eyes towards the west.
In the 1980s, they appeared overnight in the San Francisco Bay Area. It is unlikely that they crossed the country by land or water. Instead, it’s probably a problem of our own making. It is believed that the crabs were transported to California, possibly as bait. No matter how they got there, they quickly got to work multiplying.
Even still, their progress was slow at first. It took them until 2016 to travel up the coast to the interior of Washington. Since then, tens of thousands of crabs have been caught, and despite a multi-million dollar population control program, they are likely here to stay.
Then, in just four years, they spread from Washington to British Columbia. Two years later, in the summer of 2022, they reached the southern tip of Alaska. In July, a NOAA intern was walking along the shores of the Indian community of Metlakatla when he discovered a shell, the first sign that European green crabs were in the area. Then people found a few more shells. Soon after, people started seeing live crabs. Dozens of them.
Scientists believe that this accelerated population spread, continually moving north, was likely due to climate change. As ecosystems change, species follow the changing temperature band and move to new areas. There are concerns that the presence of the crabs could disrupt local ecosystems by displacing existing species for resources or eating them directly.
In particular, scientists and conservationists are concerned about eelgrass meadows in Alaska. Seagrass beds are an essential environment and resource for native Dungeness crabs and Pacific salmon. These animals, in turn, form an important part of the local economy and food supply.
While current numbers of green crabs are relatively low, environments further south are a harbinger of what Alaska will likely endure in years to come. Green crabs are an invasive species that have proven incredibly difficult to manage. According to reports, the European green crab has never been successfully removed from an ecosystem where it establishes a population. Worse, establishing a population is relatively easy for crabs.
After mating, female green crabs release nearly 20,000 eggs. Once these eggs hatch, they catch the currents and spread wherever the water takes them. Then they breed, but first they have to find each other. There’s a critical moment, just when the Green Crabs spawn in an area, where we might possibly push them away. Once they reach a critical breeding population, it becomes a war of attrition that we have little chance of winning. Worse still, the battlefield is so vast. Alaska has over 54,000 miles of coastline just waiting for the crabs to arrive. Much of it is likely too cold or lacking the necessary resources, but if the trendline is any indicator, European green crabs are already planning to keep rising. .
Chances are we won’t be able to keep the crabs at bay. Much like our would-be alien invaders, the crabs are here to stay, and we’re going to have to find a way to live together.
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