What are some examples of marine invasive species, or exotics, in the U.S.?
Panne and Spartina alterniflora are aquatic nuisance species. Creative Commons: Sandy Richard.
Carlton: If we look around the coasts of the United States, it’s actually hard to find a piece of the coastline that doesn’t have a signature invasion, especially in bays and estuaries and, in fact, along some rocky coastlines. Invasive species, or exotics, are species that have been transported from one ecosystem to another. These exotics are also called aquatic nuisance species (ANS). Some examples in the U.S. are:
The very common Japanese eel grass, which has become very abundant in the estuaries of the Pacific northwest, was probably introduced accidentally with Japanese oysters.
In Willapa Bay, Washington, the Atlantic cord grass, Spartina alterniflora, occupies thousands of acres.
In San Francisco Bay we have well over 200 species or marine invaders, including the European green crab and the Chinese mitten crab. The European green crab, Carcinus maenas, for example, was introduced to California in 1989, and since then its population has expanded rapidly from Morro Bay to British Columbia.
Southern California’s harbors and marinas have scores of exotic species that just dominate the estuaries and the floats in marinas, on the pilings, and on the moorings.
The Gulf of Mexico has a major invasion of a Pacific Ocean jellyfish, Phyllorhiza punctata, or Australian spotted jellyfish. This giant species can weigh up to 25 pounds. These jellies may be capable of consuming the larvae and eggs of commercially important aquatic species.
Florida has a host of invasive species, where over 40 exotic fishes are reproducing in fresh water, such as the Mayan cichlid from Central and South America and the Asian swamp eel.
Chesapeake Bay, like San Francisco Bay, is well invaded; a particularly outstanding new invasion is a 6-inch tall snail, the rapa whelk, from Japan, that eats clams and oysters.
Long Island Sound, and much of New England, has scores more of invaders, such as the Asian shore crab that now dominates the seascape.
What about an example of a global problem?
Carlton: We’re seeing distribution by ships of the same species around the world so that certain kinds of sea squirts, which are often large, gelatinous organisms, have been popping up in ports and harbors all over the world—Hong Kong, Sydney, Pearl Harbor, and San Diego—and in ports in the Altantic Ocean and the Mediterranean. Some of these sea squirts, which can be massive in size, can occur by the thousands of pounds on pilings and on floats. They are major fouling organisms. As a group they present a global problem.
What is the most common way of introducing marine exotics?
Carlton: There are a number of common ways to move organisms around the world. For centuries, ships and boats have been moving hundreds, maybe thousands, of species around in the world’s oceans. Organisms attach themselves to the hulls of these vessels. In modern times, ballast water (which is not bilge water) has been a major vector. We think that on any given day there may be more than 5,000 species in motion around the world via tens of thousands of ships.
What is being done to alleviate this transportation problem?
Carlton: Ballast water, as an example, has been the subject of a good deal of thought in recent decades as to what we can do to control human-mediated invasions in the sea. A number of countries around the world have established both voluntary and mandatory regulations to attempt to regulate ballast water. The challenge is what exactly should be done.
Right now the rule of thumb, the stopgap measure, is for a ship coming from a coastline, port, harbor, or estuary to exchange its water out in the middle of the ocean before it proceeds to a new port. The hope is that it has dumped organisms along with the water in the open ocean and it will arrive at its new port with organisms from the ocean but not from a foreign port. The measure has problems and challenges for both the safety and stability of the ship and also because the process is not completely effective.
Currently a lot of thinking is being devoted to how to treat the water, whether to heat it, filter it, UV it, or do something else with it so as to remove the living organisms there. Ballast water management is also a major initiative of the United Nations International Maritime Organization.
What kind of damage can marine exotics do to the environment?
Carlton: It’s a very long list; invasions harm not only the environment but also have industrial, social, recreational, and economic impacts. The list is long because so many hundreds of species have invaded the world’s coastlines.
A species can become the dominant organism in many communities, replacing and displacing native species.
In a direct sense, they impact recreation by creating huge fouling communities that need to be dealt with by recreational boaters, operators of marinas, those maintaining buoys, and so on.
There are certainly impacts on the economy. An example is the zebra mussel of the Great Lakes, Dreissena polymorpha. This small, fingernail-sized fouling mussel is native to the Black Sea of Asia. Since its introduction to North America in the 1980s, it has spread rapidly to all of the Great Lakes, the Mississippi River, and many other waterways. Hundreds of millions of dollars have been spent by the U.S. and Canada on the zebra mussel invasion.
The North American comb jelly collapsed the anchovy and other fisheries in the Black Sea, an industry worth hundreds of millions of dollars a year.
In California, a tiny sabellid worm from South Africa has impacted the abalone aquaculture industry.
There are also human health impacts with the movement of bacteria, such as cholera, in ballast water.
So the list is long, almost as long as the number of species that are invaders.
Why is it that some exotics seem benign to the environment while others take over their new home?
Carlton: Some exotic species become abundant very quickly. But we’re not so sure that any species is benign. Every species entering a new environment that becomes established is using space, using food, and using other resources. So the question of “benign” may be more a human value and human impact question, rather than impact on the environment. If we have a small introduced crustacean, a small worm, or a small mollusk, which displaces or replaces a native species, that’s not benign. The invasive species may not have a direct first-order human impact on society, but hundreds of species have invaded which have probably vastly altered the biodiversity of American waters and the seascape.
I don’t know if we can actually demonstrate that any exotic is benign, whether it’s terrestrial, freshwater, or marine. They all impact the environment as they establish themselves. Some of them become very abundant. Others spread more rapidly than others. It’s often a species-specific case. It has to do with their reproductive biology, the kind of habitat they occupy, their mechanisms of dispersal, the kind of food resources they need. Because of these and other variables, it’s often hard to predict whether a given species will spread rapidly or not unless we know that it’s the kind of species that spreads rapidly from its previous history, but even then there are surprises.
How can the general public help in the control of marine exotics?
Carlton: The public can help in two major ways: prevention and monitoring. The public is often involved advertently or inadvertently in the release of exotic species into the environment. Many exotics are sold to the public by aquarium stores, pet shops, nurseries, and even on the Internet. For various reasons, some people will actually release these into lakes, salt water, and public parks. These releases have led to some outstanding invasions. Just a basic awareness of protecting the environment by not releasing nonnative species is critical.
The other way the public can help is by monitoring the environment. This is very important to controlling invasive species. The public are often the first to notice new invasions. For example, there are millions of people walking the beaches and in our national forests compared to the relatively small number of biologists studying invasive species in the field. The public are the biologist’s eyes. When people notice some new animal or plant they’ve never seen before, they should bring it to the local nature center, the local museum, the local Sea Grant office, or the local college. Finding incipient, new populations will help tremendously in eradicating the species when their numbers are small. It’s a major management tool.
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