New Invasive on Docks
Researchers:
Sarah Cohen
Romberg Tiburon Center
San Francisco State University
E.: sarahcoh@sfsu.edu
T.: 415-338-3750
Cohen's Website
Gregory M. Ruiz
Marine Invasion Research Laboratory
Smithsonian Environmental Research Center
Edgewater, MD
E.: ruizg@si.edu
Ruiz's Website
Relevant Links:
- West Coast Ballast Outreach Project website
- Charles Lambert and Gretchen Lambert. 2003. Persistence and differential distribution of nonindigenous ascidians in harbors of the Southern California Bight. Marine Ecology Progress Series. Vol. 259: 145-161.
Tools:
Revised:
September 10, 2008
A nonnative botryllid species, matching the genotype of a sea squirt in Australia, has infested San Diego Bay. Its species name is unknown and will require genotyping to determine.. Photo: Christina S. Johnson
July 23, 2008
Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334
SAN DIEGO – The scientist lies flat on her belly and peers over the edge of the dock at the public fishing pier on Shelter Island in San Diego Harbor, looking at the veritable garden of fouling organisms along the dock’s side.
“It really is striking that it is on this pier,” says San Francisco State University professor Sarah Cohen. “Come and have a look. It is really quite beautiful.”
“It” looks like a soggy lichen, or a swatch of frog skin, and has a scientific name about as pretty: botryllid tunicate.
But not to Cohen, a marine biologist at SFSU’s Romberg Tiburon Center.
Sea Grant biologist Sarah Cohen holds the Australian sea squirt. Photo: Christina S. Johnson
“Tunicates are glorious,” Cohen croons. “They may look like a bag of water, but we share a lot of evolutionary history with them,” she explains, her hair still wet from the last sampling. Tunicates, though gelatinous water bags as adults, are born with a primitive notochord and classified in the phylum Chordata, same as us.
California Sea Grant is now funding Cohen and Gregory Ruiz at the Smithsonian Environmental Research Center in Edgewater, Md. to study the botryllid, known commonly as a sea squirt, not because of its remarkable placement on the evolutionary tree, but because the species at the dock is a new aquatic invasive, from Sydney, Australia no less.
It is hoped that the early injection of funds to map its statewide distribution and genetic diversity will prevent a costly control effort later. According to Cornell University ecologist David Pimentel, the United States currently spends about $9 billion annually to manage exotic aquatic pests such as the zebra mussel, European green crab and shipworm. Besides their economic toll, exotics, along with things like habitat destruction and pollution, are contributing to about 40 percent of all aquatic species extinctions, he says.
Nobody yet knows whether the Australian sea squirt will be added to the list of worst offenders. This is part of the goal of the Sea Grant project. Tunicate invasions on Prince Edward Island in Canada, however, suggest shellfish farmers have the most to lose from a full-blown sea squirt population explosion. These invasive tunicates are such prolific reproducers, Ruiz says. “When they grow on bivalves and shellfish nets, their shear volume and weight can be so great that it makes it expensive and laborious to harvest the mussels. Harvesting becomes very time expensive and growers lose a lot of product in the process.” The invasive tunicates, also filter feeders, compete with bivalves for food.
The dock at the Shelter Island public fishing pier in San Diego Harbor, where the sea squirt was first discovered in 2007. Photo: Christina S. Johnson
Should the sea squirt prove to be constrained by temperature to the relatively warm waters of San Diego, there is still the question of how the Australian sea squirt got here in the first place. “We want to nail the pathway,” as Cohen says, “and then take steps to close the pathway to future invaders.”
Gail Ashton, a Smithsonian postdoctoral researcher at SFSU, calls the sea squirt “an indicator.”
“Something is bringing them over, and it is probably not ballast water because the tunicate has such a short larval stage,” she says.
Given that its larvae likely would perish in transit across the Pacific, Ashton says the sea squirt may have been brought over in sea chests –– cavities on a ship’s hull that protect intake pipes for engine cooling, ballast and firefighting. Because these cavities are inaccessible to cleaning and protected from the scouring action of a ship’s slipstream, sea chests can become hideouts for the adult life stages of marine species. Once in a foreign port, larvae may establish a new, self-perpetuating colony. Currently, the sea chest idea is just a hunch, but it is plausible.
As Sea Grant Marine Advisor Leigh Taylor Johnson explains, the general assumption on marine species introductions is that large commercial ships carry species across oceans and that recreational boats then distribute these species up and down the coast.
A goal of the Sea Grant project is to test this theory by documenting the degree of genetic diversity of specimens collected from all infestation sites. Knowing where the tunicate has spread is also vital to monitor where it is going.
A lot of genetic diversity would suggest multiple inoculations from large ships, Cohen says. If the sea squirt’s invasion were basically a monoculture, as is the Caulerpa taxiofolia invasion in the Mediterranean Sea, it would suggest spreading by small boats. Like other fouling organisms, the sea squirt hitchhikes on small boat hulls to new waterways.
Sea Grant Trainee Vera Wang collects samples of the invasive tunicate at the Shelter Island dock. Photo: Christina S. Johnson.
Worrisomely, the Australian sea squirt has been identified recently for the first time in Mission Bay, a recreational waterway a few miles north of San Diego Harbor. A year ago, there were only two known infestations sites along the entire West Coast, both in San Diego Harbor. “It’s all over the place in the harbor now,” Cohen says. “But, we don’t know whether this means it is spreading really fast or whether what we are seeing is an artifact of more intense sampling.”
Cohen’s primary concern is that people ignore the significance of the sea squirt’s arrival to preventing other, future invasions. “It took the zebra mussel disaster in the Great Lakes to get people to pay attention to aquatic invasive species as a serious problem,” she says. “For sixty or eighty years, people warned that ships had the potential to bring in exotic species and that they could be a serious problem. Nobody did anything about it and then it happened. That to me is a really compelling reason to pay attention now.”
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