Hydrilla invasion and interactions with Vallisneria

Katia EngelhardtAppalachian Lab

University of Maryland Center for Environmental Science

In collaboration with former students Todd Chadwell and Lauren McChesneyand the Maryland National Estuarine Research Reserve

Rooted submersed perennial monocot that is ….

From appalachianohioweeds.org

…native to tropical Asia

www.discoverlife.org

Canopy-forming – forms thick mats at water surface

Lives in mostly freshwater habitats

Cayuga Inlet – Cornell Cooperative Extension

Grows to depths > 7m in clear water

Highly polymorphic; dioecious or monoecious biotypes

Asexual reproduction when plant fragments, tubers, roots and turions develop into new plants

Sexual reproduction in late summer. Seeds have a 50% chance of establishing.

Invasive• Grows under lower light conditions than any

other species (needs only 1% of sunlight). • No coevolved natural enemies to keep it in

check.• Has several dispersal strategies: fragments,

turions, tubers, seeds.• Grows rapidly

Listed as a

noxious weed= any plant designated by a federal, state or county government as injurious to public health, agriculture, recreation, wildlife, or property.

Hydrilla invasion atOtter Point Creek, MD

Summer 2002 – vegetation density

Hydrilla impacts on ecosystem• Slows down currents and buffers wave energy.• Enhances water clarity

• Tends to enhance production of small fishes.• Can increase dissolved oxygen concentration

but reduces oxygen circulation and can result in fish kills.

• Can be a nuisance because it can block boating channels and limit water sports.

• May enhance habitat for native submersed species, but may also displace species.

Lauren McChesney MS thesis

• In the field, plastic plants physically captured Hydrilla.

• Propagule pressure increased the chances of establishment.

Chadwell and Engelhardt 2008, J. Ecology

Does restoration of a Vallisneria slow down the invasion of Hydrilla?

• In greenhouse, Vallisneria decreased Hydrilla establishment through nutrient draw-down in closed mesocosms.

Chadwell and Engelhardt 2008, J. Ecology

Lauren McChesney MS thesis

Vallisneria versus Hydrilla

Lauren McChesney MS thesis

Vallisneria versus Hydrilla

• Vallisneria has the ability to curb the establishment and growth of Hydrilla.

• Hydrilla can facilitate the establishment of Vallisneria.

• But, Hydrilla will also compete with Vallisneria and other native plants.

In summary

Management strategies• Aggressive public education

Management strategies• Bring back competitors:– enhance water quality– reintroduce Vallisneria and other native plant

species.

Photo credit: Robert Burnett

Management strategies• Aggressive herbicide policy:

– Hard to implement in tidal rivers where water level changes constantly. – Can be toxic to other organisms.– Can lead to resistance.

Management strategies• Mechanical removal:– Mechanical cutting produces fragments that can

disperse and make the problem even worse.– Effective in isolated areas where fragments can be

controlled.

Minnetonka Lake Weed Harvesting Service

From plants.ifas.ufl.edu

Management strategies• Biocontrol: Problem with introducing another

non-native to control a non-native. Big problem if the biocontrol agent gets out of control and impacts other parts of the ecosystem.

Eradication

• Rare and not well documented• Need to start as soon as the invasion is

detected• Recommend a Hydrilla management task force