Marine life is migrating from ocean to ocean, causing ecosystem disruption. Which five immigrants are the worst?
It is not just humans who globetrot; marine (and land-based) wildlife and plants do, too. They hitch rides in a ship’s ballast tanks or stick to the hull, only to be released or come loose in an ocean far from their origin. They’re bought as pets and later released into the wild, or they’re deliberately introduced into new habitats for commercial reasons. The lack of natural predators and the availability of new, or more, food causes rapid population growth, which puts local species under pressure. Invasive species number in the hundreds, if not thousands, and depending on your point of view, the top five worst are difficult to narrow down. The following list has been compiled purely from a diver’s or snorkeler’s point of view.
Kamchatka Crab
Also known as the red king crab, this extremely large crab is native to the Bering Sea and around the Kamchatka Peninsula in the farthest northern parts of the Pacific Ocean. In the 1960s, the Russian government artificially introduced the species to the areas around Murmansk and the Barents Sea as a way of stimulating local fishing industries. However, conditions in the area turned out to be too well suited for the crabs, and they’ve since grown tremendously, wreaking havoc on populations of native marine animals, and spreading along the northern coast of the Eurasian continent all the way to Svalbard in Norway, where they call the invading crabs “Stalin’s Last Red Army.”
Zebra Mussels
Zebra mussels were introduced to the Great Lakes in the U.S. from the Black Sea by cargo ships in 1988. Since then, they’ve spread throughout the Great Lakes and beyond, reaching Canada in the north and Mexico in the south. Causing disruption of local marine ecosystems, hundreds of millions of dollars are spent each year trying to keep their numbers in check.
Sea Walnut
This little jellyfish took nearly the opposite journey of the zebra mussel mentioned above. In 1982, this ctenophore was accidentally introduced to the Black Sea from the shores of North and South America, and subsequently spread to the Caspian Sea. In both places, they’ve fed aggressively on the plankton that local fish depend on for nutrition, causing local fishing industries to collapse. Recently, they’ve been spotted in the Mediterranean, Baltic Sea and North Sea.
Killer Algae
This seaweed is native to the Pacific and Indian Oceans, but has escaped from private and public aquariums all around the world. It poses a particular problem in the Mediterranean, where it has spread aggressively and has replaced local varieties of seaweed that the fish and other marine wildlife depend on for food. California has successfully eradicated the algae, but at great financial cost and by using toxic chemicals, which further degrade the environment.
Lionfish
The rock star of invasive species, this colorful predatory fish was unknown on the American continents only a few years ago. But after hitching a ride in cargo ships’ ballast tanks from the Red Sea and the South Pacific — or being released from Miami aquariums during Hurricane Mitch, depending on what you read — they’re now abundant in the Caribbean, where their ferocious appetites are posing a threat to local marine life. Non-selective eaters, they can consume massive amounts of food. A research paper by Hixon and Albins from 2010 determined that a single lionfish could reduce juvenile fish populations in its area by an astounding 79 percent in just five days.
