A new study on marine invasives commissioned by the Tampa Bay Estuary Program is expected to report that there are far more non-native species in Tampa Bay than most people realize, says Dr. Patrick Baker, an assistant professor at the University of Florida. Most of the species, however, have had little economic impact or effect on the bay's ecosystem.

"The majority of biological invaders are never even noticed, either because the changes are so small or they occur at a level that isn't easily visible."

"That's not to say they don't have an effect - just that we don't necessarily notice the effect." he said.

Some of the non-native species may have arrived hundreds of years ago, clinging to the hulls of wooden sailing ships. The common striped barnacle (Balanus amphitrite), for instance, is not indigenous to Tampa Bay, although it's been here ever since scientists began documenting sea life in the region.

On the other hand, the distinctive coloration and rapid growth of the green mussel (Perna viridis) caused an uproar when it was discovered in 1999. Although it's still too early to determine long term consequences, scientists are closely monitoring the situation.

"There are certainly some economic impacts, because power plants may need fulltime crews to keep their seawater cooling systems working well and boat owners are going to need to clean their hulls more often," Baker said.

"The ecological costs are another question and that answer is not as clear," he continues. "They seem to be a marginal species that invades areas already altered by humans, such as bridge piers. They're very abundant in those specific habitats, but we don't know if they're limited to those areas or if they'll spread all over Tampa Bay."

The most recent research indicates that the green mussels are starting to spread into Tampa Bay's oyster beds, where they may displace native oysters. "This is a very big impact with potentially serious consequences, because oyster reefs are important habitat for many species," Baker said.

Other invaders are almost impossible to see, except for their impact on the bay's ecosystem. For instance, a small and innocuous-looking isopod (Sphaeroma terebran), which resembles a land-lubbing roly-poly, bores into the prop roots of mangrove and may be limiting mangrove distribution in the region.

"At this point, we're not saying that's what is happening here, but there was a study a few years ago that showed that it definitely impacted the distribution of mangroves in other areas," Baker said.

The TBEP study includes a thorough review of literature as well as basic sampling of bay habitat for the presence of invasive species. It may become the basis of further research, perhaps including a full-fledged rapid assessment, in which scientists with expertise in a wide variety of taxonomic specialties visit Tampa Bay and spend a week or two collecting as many samples as possible.

The preliminary study will be presented in a draft form in January, then updated and presented again in May at the Bay Area Scientific Information Symposium (BASIS) 4.

Asian green mussels (Perna viridis) were first discovered in Tampa Bay in 1999, partially jamming an intake valve at TECO's Big Bend power plant. Since then, they've become obvious residents on many bridge and dock pilings. Amy Benson, a researcher specializing in invasive species at the U.S. Geological Survey's Florida Caribbean Science Center in Gainesville, talks to Tampa Bay Soundings about the green mussel.

TBS: What exactly is a green mussel?

Benson: They're native to the Indo Pacific, ranging from the Persian Gulf to Vietnam. They're heavily cultivated as a food source in Thailand, but they're a very tropical species. The fact that they're surviving Tampa Bay winters shows that they're already adapting to this area.

TBS: How do they compare to the zebra mussel that's taking over the Great Lakes?

Benson: The green mussels aren't as bad as the zebra mussel, which can tolerate water that's anywhere from ice cold to fairly warm. Green mussels also inhabit salt not fresh water, so they're not impacting drinking water supplies. However, green mussels multiply quite easily and power plants will probably need to step up their maintenance to keep them under control. We're probably at their northern limit, although they may move further north as global warming increases water temperatures.

TBS: If they're considered a good food source, can they be harvested here?

Benson: It's still illegal to harvest shellfish from Tampa Bay because of concerns about pollution. Like most mussels, they're filter feeders, and there hasn't been any research here on their safety. We also need to discourage their spread - if people start to eat them, they may intentionally spread them.

TBS: Is there any way to control them?

Benson: I personally don't know much about predators in their native lands, maybe some crabs will eat them, but they're probably too big for most of the fish here. You can tell by their sheer numbers that there isn't much eating them. They're thick, all over bridge pilings and even starting to cover the bottom a little bit. The fact that they're occupying some of the softer sand is unusual, but they appear to be sticking to each other.

TBS: Are they having any environmental impact?

Benson: It's a little early to tell. There are a couple of studies underway but they're just now getting up and running. They may be crowding out some native barnacles and they're filter feeders so they may be denying food to native fauna. If they keep growing on the bottom, they may take over some fish habitat.

" My feeling is that it's not the end of the world. I certainly wouldn't encourage any more, but I don't see them as having the same impact as zebra mussels in the northeast."