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Hydrilla — the 9-headed marsh serpent

Fish Busters' Bulletin

Friday, December 03, 2010

Media contact: Bob Wattendorf

In classic Greek mythology, the Hydra was a marsh serpent that had nine heads to start with, but each time one was cut off, two more grew back until Hercules slew it.

Hydra makes a rather fitting root word for Hydrilla verticillata, a submersed, nonnative plant (from India) that first appeared in Florida in the late 1950s, rapidly spreading throughout much of the state.

Hydrilla has been described as "the perfect aquatic weed" because of its tolerance to conditions that prevent other native plants from flourishing, including its tolerance of low light, high turbidity and various salinities and nutrient conditions. Moreover, it can spread through fragmentation, sexual reproduction (seeds), rootlike tubers and turions (bud-like structures formed where leaves attach to the stems).

Hydrilla was introduced to Florida as an aquarium plant. With few natural biocontrols, such as native insects or diseases, the plant can rapidly occupy nearly the entire water-column of shallow lakes. It can affect navigation, water storage and water flow, which is needed to prevent flooding. It can spread on boat motors or trailers even after it appears to be thoroughly dried out, and it can survive the virtually dry soils of dewatered lakes and rapidly take over when the lake refloods.

Chemical and other control efforts, including biological and mechanical approaches, cost millions of state dollars annually.

The Florida Fish and Wildlife Conservation Commission (FWC) is creating a long-term black bass management plan, and one of the critical aspects to consider is that of aquatic plant management and how to deal with exotic plants such as hydrilla. In 2008, the legislature moved invasive plant management from the Department of Environmental Protection to the FWC. An intra-agency task force is actively working to develop new plans and processes for managing hydrilla.

What makes invasive plant management so complicated is that hydrilla can benefit recreational fisheries and waterfowl populations and even help support endangered species such as the snail kite. On the other hand, conservation philosophies and the economics of attempting to manage it provide a compelling reason to try to keep it out of new areas and control it before it harms navigation, flood control, potable and irrigation water supplies, recreation and the beauty of lakes.

A recent meeting dealing with management plans for hydrilla on Lake Tohopekaliga, co-hosted by the FWC and the U.S. Fish and Wildlife Service, highlighted some of the controversy.

"Lake Toho contains large amounts of hydrilla, which can cause navigation problems and limit access to boaters," said Bill Caton, the FWC's Invasive Plant Management Section leader. "This plant also provides an abundant food source and habitat used by a nonnative variety of apple snail that lives in the lake." In turn, the snail is eaten by snail kites, which are among the most endangered birds in Florida, making Lake Toho one of the few areas in the state where kites can find plenty of food.

Consequently, the FWC and the USFWS will adjust when and where hydrilla is treated so enough snails will be available when kites nest next spring. The Audubon Society and the FWC want to protect snail kites. Other stakeholders, like the Florida Freshwater Fisheries Coalition, want enough submersed plants to provide good fish habitat but also open areas for anglers to catch fish. If too much hydrilla is left untreated, plant biomass could affect flood control.

Now that biologists have laid out these pros and cons of hydrilla treatment in various situations, the FWC is reviewing the first draft of the Black Bass Management Plan (

In the meantime, does anyone know where we can find another Hercules to take on our Hydra-illa issue? You can contribute to the dialogue by completing a brief survey on aquatic plant management at

FWC Facts:
Manatees, like their relatives - elephants, hyraxes and aardvarks - have a long gestation period and can regrow their teeth.

Learn More at AskFWC