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February 9, 2009
Invaders to our coastline come in all forms--plants, animals, parasites--but they all have one thing in common: By their very presence, they alter the balance of ecosystems that produce some of our most sought-after commercial and recreational species of fish and underwater food. Although estimates vary as to the economic impact of these unwelcome newcomers, some put the cost to businesses as high as $100 billion a year. The mitten crab--which like any good villain has an a.k.a., in this case either the big binding crab and the Shangahi hairy crab--is at the top of the list of invasive species that are an almost constant threat to what we have come to think of as the natural population of our waters.
A recent article in the Boston Globe said that scientists know of about 50 non-native species off New England's coast that they probably can't do anything about, including a European seaweed known as "dead man's finger" that arrived in the 1960s and is now being tied to the destruction of cod and sea urchin habitat. That species, codium fragile, takes root in eel grass beds, which are nurseries for juvenile fish and lobsters. Because if a piece breaks off it can regenerate, the codium is out-competing the eel grass and kelp and taking over. So what's the big deal? Seaweed is seaweed, right. No. Because the codium branches are round and spongy and about the thickness of an adult human finger, they inhibit the movement of fish, lobsters and sea urchins and halt their reproductive cycles. That in turn hurts other larger fish that eat the immature ones. No food, no fish. The dead man's finger could be pointing towards disaster.
THE SPACE INVADERS
Not all non-native species are considered invasive. To earn that label, you have to be a real rabble-rouser. A species becomes invasive only if it replaces an existing lifeform and disrupts an ecosystem. Take the gruesome cymothoid isopod.
Known by many as a "tongue biter," this parasite hooks its legs into the tongue of a fish, particularly bluefish and striped bass in the mid-Atlantic states, and eventually the tongue falls out.
Scientists cannot pinpoint where this parasite originated, but they have not yet found a connection between the tongue-replacing tenants and a decrease in the lifespan of fish. So even though it doesn't get any more invasive that a tongue biter, that doesn't necessarily make it an invasive species.
The Asian shore crab, first spotted along the New Jersey coast in 1988, quickly became more populous than its green crab cousins in many areas of Long Island and New Jersey and now are the dominant crab found on rocky shorelines. Because of their ability to withstand not only tropical waters but sub-freezing conditions, their breadth reaches from Cuba to Maine. The Asian crab is a more aggressive feeder that the green, so it can bully its way into pre-existing turf, often feeding on the larva of its competitors which include other crabs and even lobsters. Pesticides and global warming have been blamed for the lobster die-off in Long Island Sound, but researchers are quick to point out the corresponding timeline between the ascent of the Asian crab and the descent of the lobster.
Another seemingly innocuous creature that can cause eco-chaos is the sea squirt. These animals that look like plants cling to boats or pilings and suck water in one end and out the other. When they latch onto moorings they create a thick crust that isn't only an aesthetic blight, but because they release a noxious substance as a byproduct of their metabolism, prevents other creatures from mounting to the same form and also discourage predators. It is also an economic nuisance to aquaculture structures used in the farming of oysters and other shellfish. Yet the scariest occurrence of the sea squirts, or tunicates, may by at Georges Bank, where the animal has been seen to reach very high densities, covering large areas of ocean floor like an impenetrable pancake batter and choking it off.
By 2002 the first Atlantic lionfish was captured and today they can be spotted all along the southeast coast of the United States and, depending largely on water temperatures, as far north as New York. Commercial and recreational anglers have been known to hook them, too. Although scientists have been unable to prove that lionfish are reproducing, their quickly-growing numbers strongly suggest that this is the first time that a western Pacific fish has populated the waters of the U.S. Atlantic coast. Lionfish, a popular specimen for aquarium enthusiasts (who are believed to have introduced them into their new waters by dumping), are easily identified by their black and white stripes and their long, dangerous spikes that contain a venom that can kill prey, discourage attackers, and cause severe pain in humans. They sport a voracious appetite that belies their dainty, delicate look, and they feed mostly on small shrimp and larger fishes, including the young of commercially important species such as snapper and grouper that are bred in the same reefs lionfish are starting to dominate. Because there was very little research on the hard-bottom habitats where lionfish have been reported in the Atlantic, it is difficult to determine what the ecological impact of lionfish is on their new ecosystem. "As a result, there is nothing to compare the present situation to," Whitfield wrote. "It would have been nice to be able to do a 'before and after' comparison, but it is not possible." About the only thing that can slow the lionfish spread is temperature. Because they are a tropical fish, they require certain warmths that not all waters provide. But scientists believe that in the warmer waters of the Atlantic, lionfish could soon have a population density that approaches or even exceeds their numbers in their native Pacific.
These critters not only impact delicate ecosystems, they're just plain gross!
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