An army of green crabs is preparing to invade Alaska
in the documentary series Alien Invasion: Are We Ready? (Right now on Peacock!) Scientists and military professionals imagine what an actual alien invasion might look like. Ever since the idea of possible extraterrestrial intelligence hit the mainstream, we’ve been low-key obsessed with thinking about how events might unfold and what, if anything, we could do to stop the invasion. Countless books, movies, and video games explore the question, and the genre probably won’t go away.
While we’ve been watching the sky, we’re seeing a slower, more mundane invasion here on Earth. Or, more precisely, in the water. Over the past two centuries, a growing army of European green crabs has been slowly making its way across North America and appears to be on a new front. They are well equipped too. Crabs seem to be nature’s favorite form. Through conquest or evolution, we are all destined to become a crab someday…maybe.
European green crabs first appeared in America nearly 200 years ago, possibly as a result of colonization. For most of the intervening period, they were largely cut off from the east coast. Large swaths of land are not the typical resting places of most crabs, so our beaches on the Pacific Ocean were safe. Or so we thought. But like the elves of Middle-earth, the eyes of the green crabs were to the west.
In the 1980s, they appeared seemingly overnight in San Francisco Bay. It is unlikely that they made their way across the country by land or navigated by water. Instead, this is probably a problem of our own making. It is believed that the crabs were brought to California, possibly as bait. But when they got there, they quickly set about multiplying.
Even so, their progress was slow at first. It took them until 2016 to make their way up the coast to inner 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, over the course of just four years, they spread from Washington to British Columbia. Two years later, in the summer of 2022, they reach the southern tip of Alaska. In July, a NOAA intern was walking along the shores of the Indian community of Metlakatla when they spotted a shell, the first sign of European green crabs in the area. Then people found a few more shells. Soon after, people started seeing live crabs. dozens of them.
Scientists believe that this accelerating population spread, constantly moving north, may have been driven by climate change. As ecosystems change, species follow the changing temperature range and move to new areas. There are concerns that the presence of crabs will disrupt local ecosystems by competing with existing species for resources or eating them outright.
In particular, scientists and conservationists are interested in Alaskan eel-grass meadows. Eel grass meadows are a critical environment and resource for both native Dungeness crabs and Pacific salmon. These animals, in turn, are an important part of the local economy and food supply.
While the current number of green crabs is relatively low, environments farther south are a harbinger of what Alaska may endure in the years to come. Green crabs are an invasive species that has proven to be very difficult to deal with. According to reports, the European green crab has not been successfully removed from any ecosystem where it is establishing a population. Worse yet, creating a population is relatively easy for crabs.
After mating, female green crabs release approximately 20,000 eggs. Once these eggs hatch, they catch the currents and scatter anywhere the water will take them. Then they reproduce again, but first they have to find each other. There is a critical moment, just when green crabs appear in an area, when we might be able to fend them off in practice. Once they reach a critical spawning clan, it becomes a war of attrition that we are unlikely to win. Even worse, the battlefield is far-reaching. Alaska has more than 54,000 kilometers of coastline just waiting for the crabs to descend. Most of them are probably just too cold or lack some necessary resources, but if the trend line is any indication, European green crabs are already making plans to continue their advance higher.
Odds are we won’t succeed in keeping the crabs away. Like so many eventual alien invaders, crabs are here to stay and we’ll have to find a way to live together.
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