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State of the Bay  »  Invasive Species

State of The Tampa Bay Estuary Invaders

Brazilian pepper is among the most invasive plants along the shores of Tampa Bay

Invasive species are plants or animals that have been introduced from another part of the world into a native, or endemic, ecosystem, resulting in environmental, economic or human health impacts. Invasives are particularly aggressive species that can displace and overtake native populations, reducing biodiversity and diminishing biological integrity. According to the World Conservation Union (IUCN), invasive species are second only to habitat loss as a cause of extinctions worldwide.

The 1999 discovery in Tampa Bay of an exotic mussel native to Asian waters reinforced the need for a baywide strategy to address the potential environmental threats posed by aquatic invasive species. As a result, an Invasive Species Action Plan was developed and is included in this update of the Comprehensive Conservation and Management Plan. The plan calls for a two-pronged approach focused on educating the public about the impacts of invasive species and ways in which residents can help prevent invasions, and additional research into the extent of the problem in Tampa Bay.

A literature review and field survey of aquatic nuisance species commissioned by TBEP in 2002 identified 55 known, suspected or likely marine invaders in the bay. Additional research has explored the potential for an invasion of Tampa Bay by the toxic algae, Caulerpa taxifolia Mediterranean strain, concluding that the bay faces a relatively low risk of introduction of this extremely harmful species at the present time.

State of The Tampa Bay Estuary Invaders Mussels

On the other hand, the Asian green mussel (Perna viridis) has rapidly spread throughout the bay and beyond, with recent sightings in northeast Florida, southern Georgia and northwest Florida. Within one year of its discovery in Tampa Bay, it had spread south to the Charlotte Harbor estuary system. At first, the mussel colonized primarily manmade structures such as bridge pilings and docks, but has now been documented in Tampa Bay in bare sand or mud flats and interspersed with seagrasses. TBEP is currently sponsoring research into the relationship between the green mussel, water quality and seagrass recovery in the bay to gain a better understanding of the environmental impacts of this highly successful invader.

The Asian green mussel is thought to have arrived in the bay in ballast water -- water that is carried in the underbellies of ships to maintain buoyancy on the open sea. In fact, ballast water is a primary avenue through which numerous invasive organisms are believed to have been transported from one waterway to another. The international nature of modern-day shipping dramatically increases the potential for marine organisms to "hitchhike" around the globe - and scientists estimate that an average of 40,000 gallons of ballast water is released in U.S. coastal waters every minute.

As many as one-quarter of all the ships entering the Port of Tampa contain ballast water which may be discharged into Tampa Bay, according to port officials. Several regional studies are underway to characterize the risk posed by this water, and to test treatment and assessment techniques. National regulations approved in 2004, to be implemented by the U.S. Coast Guard, will require mandatory ballast water treatment for all commercial ships entering U.S. ports. The most feasible treatment option at present is open ocean exchange - the discharge of ballast in offshore waters where high salinity levels dramatically reduce the survival rates of hitchhiking plants or animals.

State of The Tampa Bay Estuary Invaders Plants

Significant attention and resources have been devoted to preventing or removing invasive plants, especially Brazilian pepper, Australian pine and other coastal invasives. Most habitat restoration projects in the bay watershed involve eradication of invasive plants, and private developers also are often required to remove invasives as part of mitigation for wetland impacts. However, it is highly unlikely that invasives will be eliminated from all public lands, because of the extent of the problem and the high cost of removal treatments.

Several agencies and organizations recently launched an effort to encourage homeowners to remove invasive trees, shrubs and vines in their backyard landscapes, recognizing that even a single plant may serve as a seed source to infest nearby parks and preserves. TBEP, in partnership with Florida Sea Grant, the Hillsborough Invasive Species Task Force, the Cooperative Extension Service and others, has produced or supported the production of a complete package of materials designed to help homeowners identify common invasive plants and teach them safe and effective removal techniques. The packet includes a seminar presentation, a field guide to invasive plants, and a video with step-by-step instructions for treatment and disposal of invasives.

Educational initiatives also are being planned for boaters, pet shop owners, aquarium enthusiasts and others who may unwittingly introduce invasive plants or animals into the bay system.

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