In a time when many worry about terrorists crossing our borders, and increase security measures to prevent this, many biologists are also concerned about another group of "alien invaders." Those of us on Catalina are aware that of the 600+ species of plants growing on the island, more than one-third are such exotics. These are species which are native to Europe, South America, Asia, South Africa and other geographically remote regions... not even to North America!
For a plant to be native to a location, it must be naturally occurring in the region and disperse to that location through natural means. For example, after the island emerged from the sea providing new habitat for species to colonize, a bird may have flown over here and excreted a Toyon berry. Since the Toyon berry is native to southern California, and bird transport is a natural form of dispersal, it is considered native here.
On the other hand, a tree tobacco plant native to South America might reach southern California via early Spanish explorers or colonists. Because it was transported by humans, biologists do not consider it native. This is not because humans are not a part of nature, but because our actions occur in very short time frames which do not give the other species in an ecosystem a chance to evolve and adapt to the newcomer. Then in 1902 a large fire on the mainland, coupled with Santa Ana winds, apparently blew large numbers of the tiny seeds to Catalina and the plants started sprouting all over the island in the next few years according to early botanist Blanche Trask. Biologically this is an alien invasion!
"Okay, Dr. Bill," you ask "what does this have to do with the undersea world? Let me continue. In these days of modern shipping with very large container and other ships traveling rapidly between the continents, it is far more possible for marine species from another part of the world to reach our shores. When ships were much slower, marine life attached to their hulls would often not survive the long voyage. Now it is possible for marine life, either as planktonic larvae or adults, to cross the Pacific in a short time in the somewhat protected bilge water or even on the hull.
Of course species from tropical areas generally would not survive introduction into our colder waters. However when we trade from cooler water areas like Europe and northern China, species may adapt to conditions in our water and thrive. In their new surroundings, these introduced aliens may not face the diseases or predators that kept them in ecological balance in their native waters. They increase exponentially and may overeat their new food sources, destroying populations of native marine life. In addition the exotic species may also introduce new parasites that can infect native species here that lack any resistance to them. The speed at which these processes may take place prevents nature from adapting to these new threats.
An example of this is the Chinese mitten crab, native to the Yellow Sea. In 1992 it was discovered in San Francisco Bay and the population has grown rapidly. So what? A delicacy in China, this crab has parasitic flukes inside it which can be transferred to humans who eat them. They also cause stream bed erosion by burrowing into the mud. and damage the nets and catch of fishermen. No one knows for sure how they arrived in the Bay, but it is probably more than coincidence that they were discovered shortly after trade with China began.
Other examples closer to home include Caulerpa taxifolia, the so-called "killer algae," which has been discovered in San Diego and Orange Counties. A native of the Caribbean, this plant was often used in salt water aquariums. Strains of it developed in a German aquarium business invaded the Mediterranean Ocean years ago, with Caulerpa now covering some 30,000 acres there. Although it's ecological impact has been questioned, most of the statements come from those allied with the aquarium trade that profits from its sale. It is believed the invasion near Carlsbad (CA) in 2000 may have occurred when an individual dumped the contents of their home aquarium in a storm drain or directly in the ocean. It cost nearly $1 million to eradicate Caulerpa there.
Another invasive species, Undaria pinnatifida, was recently discovered off the White's Landing area on Catalina by Steve Madaras and a Japanese diver. This kelp is a native of Japan, but has invaded many areas including Monterey Bay, Santa Barbara and Catalina all in the early 2000's. It is interesting to note that a while prior to the discovery of this alga, a large commercial ship had been anchored in the area reportedly cleaning its hull. Hmmm. It is feared that this species may compete with our giant kelp forests. A similar invasion of our waters by the Japanese fern (Sargassum muticum) occurred several decades ago. Fortunately such biological invasions around our island are being monitored by marine botanist Dr. Kathy Ann Miller at the Wrigley Institute for Environmental Studies.
Not all invasive species pose significant ecological problems. The ones that do need to be destroyed in the early stages of invasion when control may be possible. Of course the best thing to do is to stop them before they get here by cleaning the hulls and bilges of commercial ships before they arrive in port. Perhaps the Department of Homeland Security should equip its immigration officers with pictures of the potentially most invasive marine species along with those of known terrorists of the human species. Passport please? Now before you start to write a letter to the editor, I know that measured by human scales the two are not equivalent threats... but consider the potential impact on our giant kelp and other kelp forest dwellers. Remember, it was giant kelp that helped us win World War I... it deserves our thanks.
© 2003 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.
Image caption: Caulerpa taxifolia image courtesy
of Dr. Thomas Belsher, IFREMER (French Research
Institution for Exploitatation of the Sea); Undaria pinnatifida courtesy of Dr. Kathy Ann Miller,
USC Wrigley Institute for Environmental Studies (WIES)
This document maintained by
Dr. Bill Bushing.
Material © 2003 Star Thrower Educational Multimedia