Non-native invasive plants threaten lake ecosystem

OKEECHOBEE — Aquatic vegetation on Lake Okeechobee is often a mix of native plants that are beneficial to the ecosystem, non-native invasive plants that harm the ecosystem, and some plants that may be helpful or harmful depending on conditions.

The efforts of government agencies to control the invasive plants sometimes draw criticism from fisherman, who say the herbicides used to kill the “bad” vegetation also harms the native aquatic plants, and that spraying chemicals in the lake adds toxins to the muck on the lake bottom.

FWC officials counter that while they also use biological controls, some invasive plants can only be controlled by chemical spraying. They say spraying plants while the plants are small keeps them from spreading and growing into a larger problem.

Mechanical harvesting of aquatic plants, which would help reduce the nutrient load as well as remove the plants, has been attempted in pilot projects in the past, but also has a down side. Mechanical harvesting is more expensive than spraying. Since the invasives may grow in the same areas as native plants, mechanical harvesting removes some of the “good” plants with the “bad.” In addition, mechanical harvesting may also kill small fish that are pulled out of the lake with the aquatic vegetation.

“Common Aquatic Plants of Lake Okeechobee,” by K.A. Langeland and C.C. Jacono documented a number of beneficial native plants, harmful non-native plants and some native plants that can be a problem, depending on the circumstances. The research paper was published in 2015.

“Aquatic and wetland plants are essential to the ecology of Florida lakes, such as Lake Okeechobee, but they can also pose ecological and water use problems. Plants provide food and habitat for sport fish and other wildlife, help improve water clarity, and help stabilize shorelines and bottom sediments. However, certain fast-growing species of plants can become too abundant, which can be unhealthy for lakes and cause problems for recreational water uses, navigation, and flood control,” the authors note.

“Many plants that are considered a problem to Lake Okeechobee were brought here from other parts of the world. When these non-native plants grow out of control to out-compete native plants and alter the natural environment, they are called invasive. Some plants, especially invasive plants, must be managed on Lake Okeechobee to protect the health and recreational uses of the lake. Lake Okeechobee is unique because of its vast size (730 square miles), shallow water (9-ft average depth), high nutrient levels, and extensive marsh (147 square miles), which is heavily used for fishing, hunting, and birding. Lake Okeechobee, especially its marsh, is home to numerous plant species that play roles in the lake’s ecology.”

Aquatic plants fall into categories:

• Emersed (or emergent) plants occur along the shoreline and in the shallower zone. They are rooted to the bottom and grow above the water surface;

• Submersed plants occur mostly in deeper zones. They are usually rooted to the lake bottom and mostly remain beneath the water surface;

• Floating-leaved plants are rooted to the bottom and have leaves attached underneath the water. The leaves float on the water surface, with some leaves somewhat emersed; and,

• Floating plants are not attached but float freely on the water surface and can occur anywhere on the lake from the shoreline to deep water.

The following articles include: Native plants provide habitat for fish and wildlife, Overgrowth of some native plants can require management, and Non-native invasive plants threaten lake ecosystem.

Native plants provide habitat for fish and wildlife

OKEECHOBEE — “Common Aquatic Plants of Lake Okeechobee,” by K.A. Langeland and C.C. Jacono, documented a number of beneficial native plants, harmful non-native plants and some native plants that can be a problem, depending on the circumstances. The University of Florida Institute of Food and Agricultural Services research paper was published in 2015.

Plants that are native to the lake and which provide beneficial habitat and food for fish and wildlife include the following, according to the study.

Maidencane. Courtesy IFAS, Vic Ramey.

• Maidencane, an important native aquatic grass that stretches along the coastal plain from New Jersey to southern Florida. Maidencane forms the backbone of the wet prairies inhabited by the Florida panther, offers prime forage for deer, and creates upright habitat in the shallow marshes, ponds, and shorelines of Lake Okeechobee. Maidencane is a paradise for the insects, small reptiles, and fish that support wading bird populations. Its fibrous stems and hefty underwater runners are good nesting material for larger birds such as cranes which build their nests on shallow, emergent vegetation. The seeds of maidencane, though not plentiful, are nutritious. Where it grows into deeper waters that lack a firm mineral bed, maidencane is used as nest material by largemouth bass. Unfortunately, this important plant disappears if seasonal fluctuations are eliminated, such as when water levels are permanently increased, stabilized or lowered.

• Arrowheads are hefty shoreline plants that hold their large leaves upright on sturdy stalks, while becoming very spongy at the base.

• Spikerush (also called needlegrass) is not a rush or a grass, but a sedge that grows like a field of olive-colored straw leaning this way and that in the shallow marsh. Spikerush fields are excellent duck habitat, offering a thick, camouflaged cover and food in the form of both tubers and seeds. The Florida mottled duck, a non-migratory mallard, is especially known to eat its seed. The rather open, vertical landscape produced by large stands of spikerush is prime foraging habitat for the endangered Florida snail kite, which must readily see its apple snail prey to capture them.

Southern amaranth. Courtesy Ann Murray, IFAS.

• Southern amaranth (also called giant pigweed) is a fast-growing giant of the marsh that returns from seed every spring on high mounds along shorelines that dry down or on levees around Lake Okeechobee. This plant usually has wide, red, basal stems, which offer hollows for benthic organisms and resources for wildlife at the end of the growing season.

Swamp rosemallow. Couresty IFAS K.A. Langeland.

• Swamp rosemallow (also called marsh mallow) is a towering native in the marshes of Lake Okeechobee and is related to the cotton plant and ornamental hibiscus. The swamp rosemallow is a summertime beauty that offers high perches and vantage points to marsh birds.

Giant bulrush. Courtesy IFAS, Vic Ramey.

• Giant bulrush is the tallest rush at Lake Okeechobee, growing to a height of 6–8 ft. Several species of birds eat the seeds of bulrushes, and the stems of giant bulrush are important to midges. Although an irritant to humans, midges are a valuable food for fish.

Fish do not eat the midge larvae, waiting instead until the midges turn into flying adults before feasting. Two types of bulrush grow in Lake Okeechobee, one with soft stems, called softstem bulrush, and one with very stiff stems, called buggy whips or pencil grass in Florida.

Common reed. Courtesy IFAS, Ann Murray.

• Common reed is a cane-like grass that grows on the levees and ditch banks around Lake Okeechobee. Its stands offer shelter for redwing blackbirds and puddle ducks. This is not the invasive “phragmites” of the northeastern U.S., but our Florida native subspecies which is becoming more frequent as our environment changes.

• Pondweed (also called peppergrass) roots deep in the lake bed, but its soft branching stems bring its leaves up to the water surface. Flowers produce plump seeds that are eaten by diver and puddle ducks. The underwater stands of this plant are full of insects and create some of the best fishing zones on the lake. Largemouth bass are fond of pondweed in the littoral zone of Lake Okeechobee. This is probably because within every surface square yard of pondweed, fish will find numerous grass shrimp, segmented worms, and midges available as high-quality food.

Eelgrass. Courtesy, IFAS K.A. Langeland.

• Eelgrass (also called tapegrass or ribbongrass) has ribbon-like leaves that are a 1/2-inch wide and more than 3 feet long. When left undisturbed, eelgrass grows in dense underwater beds, creating some of the best habitat for fish and the insects that fish eat.

Eelgrass beds are favorite areas for largemouth bass, and more than 20 different species of insects make their home in eelgrass beds in Lake Okeechobee. According to the Florida Fish and Wildlife Conservation Commission, every square yard of eelgrass contains an average of 67 grass shrimp, 1,900 segmented worms, and over 13,000 midges, which are food for a variety of locally occurring fish.

Southern naiad. Courtesy K.A. Langeland.

• Southern naiad looks like thin branching twigs underwater. It builds up a beneficial habitat for fisheries. The Florida mottled duck and other dabbling and diving ducks eat naiad — seeds and all.

Coontail. Courtesy IFAS, Vic Ramey.

• Coontail consists of branching masses of stiff strands that grow underwater without being rooted to the lake bottom. For some fish, like the Everglades pygmy sunfish, underwater structure from aquatic plants like coontail is preferred over bare lake bottoms for spawning. The juvenile fish find nursery refuge there, as do small animals (zooplankton) that harbor safely in the forked leaf masses. In the fall, waterfowl eat the fruits produced on coontail strands.

American lotus. Courtesy IFAS – K.A. Langeland.

• American lotus (also locally called chinquapin) is a prominent native plant on Lake Okeechobee. The enormous circular leaves and fragrant, pale yellow flowers arise from long, slender stems rooted in the lake bottom. Wildlife can eat the seeds before they harden. The leaves and stems provide structure and cover for fish, but dissolved oxygen can become low under a dense canopy of leaves.

Spatterdock. Courtesy IFAS K.A. Langeland.

• Spatterdock (also called bonnet or cow lily) differs from the American lotus by its shiny, dark green, oval-shaped leaves with deep clefts. This native plant forms thick, hard, underwater stems, which support reproduction of largemouth bass in lakes with soft bottoms. Male largemouth bass will sweep the stems of spatterdock clean of sediments to use in their nest construction. The yellow waterlily borer, an effective fish-bait, can be found where they have burrowed into the leaf stems of spatterdock.

Waterlillies. Courtesy IFAS K.A. Langeland.

• Waterlilies (also called pads) differ from lotus and spatterdock by having circular floating leaves marked by a cleft that runs nearly 1/3 of the length to where the stem attaches on the leaf underside. Most common is fragrant waterlily, with its many-petaled white flowers, although the yellow or Mexican waterlily, with smaller yellow flowers, also belongs on Lake Okeechobee. Waterlilies grow as dense stands in shallow water, firmly anchored by hefty, bulb-like bases. Ring-neck ducks feed heavily on lilies; their crops have been found to contain 500–1,000 white waterlily seeds at one time.

• Pennywort (also called dollarweed) has scalloped edging on its disk-shaped leaves, a central white spot where a spongy, upright stalk attaches underneath, and thick runners that creep along shorelines and extend in tangles into the water. Pennywort adds value to Lake Okeechobee by stabilizing shorelines, offering good places for fish food (which hide at the shaggy stem joints), and producing seed for birds on its tiny “Queen Anne’s lace”-like flowers.

Duckweed. Courtesy IFAS K.A. Langeland.

• Floating bladderwort is primarily an underwater mass of threadlike leaves carrying small, hollow sacs that trap and digest small prey. The habitat it provides to zooplankton, insect larvae, and other small swimmers likely offsets the number it consumes.

• Duckweeds are the smallest of Lake Okeechobee’s floating plants and are usually found mingling among larger plants that afford them protection from wind and waves. Duckweeds create nursery cover for fish and provide green meals rich in protein for waterfowl.

Mosquito fern. Courtesy IFAS, David Sutton.

• Mosquitofern plants have a textured, lacy appearance formed by a number of tiny, overlapping fronds scattered across their branched, floating stems. Colored from green to deep red, they are common in protected areas of the lake. Although the plants themselves are rarely eaten, their dry surfaces and underwater spaces make good homes for the insects eaten by frogs, wading birds, and other marsh animals.

Overgrowth of some native plants can require management

OKEECHOBEE — Even native plants can grow so rapidly that they become a problem for the Lake Okeechobee ecosystem under certain conditions. For example, high levels of phosphorus encourages the growth of cattails, which can push out other native vegetation and prevent water from circulating in the marshes.

According to “Common Aquatic Plants of Lake Okeechobee,” by K.A. Langeland and C.C. Jacono, plants that provide some environmental benefit, but still must be managed include the following:

Smartweed. Courtesy IFAS, Vic Ramey.

• Smartweed grows near the shoreline in mounded areas and at wet sites that occasionally dry. It is most noticeable in late summer, when clouds of pink or white flowers form masses on spikes above its stalks of green, lance-shaped leaves. Smartweed can be identified during the rest of the year by the papery sheath that wraps the stem at the swollen joint where the leaf meets the stem. The sheath is topped with a fringe of bristles. Dabbling ducks, including fulvous tree ducks, mallards, teals, and ring-necked ducks, are attracted to the hard, dark, shiny seeds that fall and collect in great numbers in the shallow lake bed near smartweed colonies. Sometimes managing smartweed is required to maintain boating access.

Cattails. Courtesy IFAS K.A. Langeland.

• Cattails at Lake Okeechobee are mostly the type that forms a flower spike, which is naked at the tip and grows as high as the straight, flat leaves. Cattails are valuable to small birds, such as redwing blackbirds and migrating marsh wrens, which find insects to eat within the stands. Cattails can have massive growth and form dense stands accessible only to airboats. They are sometimes managed with herbicides on Lake Okeechobee to keep boating access open and allow water circulation into marsh areas.

Water lettuce. Courtesy IFAS K.A. Langeland.

• Waterlettuce creates large, floating mats of plants. Scientists debate whether it is native or non-native, yet it causes problems similar to those caused by water hyacinth. If not controlled, they form continuously growing floating masses that destroy other plant communities and impede boat access and flood control. Waterlettuce is managed for maintenance control with herbicides.

Non-native invasive plants threaten lake ecosystem

OKEECHOBEE — Like most Florida waterways, Lake Okeechobee’s habitat is threatened by invasive, non-native plants that push out native vegetation. “Common Aquatic Plants of Lake Okeechobee,” K.A. Langeland and C.C. Jacono, lists a number of harmful aquatic plants. The UF/IFAS research paper was published in 2015.

Hydrilla. Courtesy, IFAS, K.A. Langeland.

• Hydrilla was introduced from Asia as an aquarium plant. It is now prohibited as a “Noxious Weed” by federal and state governments. It grows in tangled strands that branch horizontally underwater and extend upward at the same time to form dense mats at the surface. Because it is able to grow under poorly lit and turbid water, hydrilla holds a competitive edge over other plant species, including the native pondweed. It almost always turns a mixture of naturally occurring plants into areas where little plant life other than hydrilla exists, eliminating plant diversity, snagging propellers, and making fishing difficult.

Torpedo grass. Courtesy IFAS, Vic Ramey.

• Torpedograss is an emersed grass that grows from extensive rhizomes (underground stems). Torpedograss is an invasive plant that was introduced to Florida from South America. It grows so densely that it prevents other plants from growing. Torpedograss is managed on Lake Okeechobee, and efforts are underway for long-term reduction in the lake by using a combination of burning during low water periods and herbicide applications.

Trompetilla. Courtesy Sellers.

• Trompetilla (also called West Indian marsh grass) is a large, invasive grass with wide leaves and long, lanky stems that both creep across and grow upright from the water surface. Originating in Central and South America, this grass has mechanisms for coming back and producing seeds every year. In wet springs, when the lake bed remains under water, plants will re-grow from underwater stems. During droughty springs, when the lake bed dries down, plants can come back from seeds. Because of its added ability to push out

Wild taro. Courtesy IFAS, Alison Fox.

good native plants, trompetilla is targeted for herbicide treatment on Lake Okeechobee.

• Wild taro has elongated, heart-shaped leaves held above the water surface by a thick stalk. The stalk attaches to the undersurface of the leaf at a nearly centralized point, where three major veins meet. Wild taro is non-native and undesirable in Florida water bodies. Steer clear of this plant because calcium oxalate crystals deposited throughout its tissues are poisonous and can induce a severe skin reaction on pulling or cutting with a string trimmer. Herbicides are used to counter the growth of wild taro in Lake Okeechobee.

• Primrosewillows are broadleaved plants commonly infused with red on the stems and leaves. They produce flowers with 4–5 yellow petals that drop when touched. Seed pods are elongated capsules called “seed boxes” that split open late in the season and drop large numbers of small, black seeds, which are eaten by puddle ducks and ground-feeding birds. More than a dozen different species of primrosewillow might be growing at one time in the marshes and margins of ditches and roadbeds around Lake Okeechobee. The most common is the invasive Peruvian primrosewillow, which has

Crested floatingheart. Courtesy IFAS K.A. Langeland.

larger flowers than other primrosewillows, a bushy frame, a woody base, and boundless growth that often requires control with herbicide.

• Crested floatinghearts resemble miniature waterlilies, except that the cleft on the leaf is not as pronounced and is rounded at the edges, giving an overall heart-shaped appearance to the floating leaf. Crested floatingheart has rapid rank growth and is an increasing problem in Lake Okeechobee and other water bodies. It is treated with herbicide to prevent its spread.

Water hyacinth. Courtesy K.A. Langeland.

• Waterhyacinth is recognized by its inflated, bulbous leaf stalk and, when present, its spike of blue to purple flowers with an upper yellow blotch. While it is found throughout Florida, it is not a native plant and is highly invasive, meaning it causes environmental and/or economic harm. It is native to the upper basin of the Amazon River and was brought to this country as an ornamental curiosity for ponds at the 1884 World’s Fair Exposition in New Orleans. It has caused problems on Lake Okeechobee since 1905. The USDA has released three different kinds of insects for biological control of waterhyacinth. These insects work to reduce the size and aggressiveness of waterhyacinth. Herbicides must be used to keep waterhyacinth at the lowest levels possible (maintenance control) on Lake Okeechobee. When waterhyacinths are not controlled, they form continuously growing floating masses that destroy native plant communities and impede boat access and flood control. Ten waterhyacinth plants can grow to cover an acre during a single growing season.

Tropical watergrass. Courtesy IFAS, Colette Jacono.

• Tropical watergrass, first found on the lake in 2007, is an invasive grass that has already impacted lake ecology by creating massive, impenetrable mats. The floating mats consist of tropical watergrass stems, floating debris, and other live plants. The long, tough, upright leaves of tropical watergrass are recognizable as they arise from their stems that float just under the surface. Tropical watergrass flowers in the fall months, producing millions of seeds that latch onto clothing and contaminate gear, increasing the risk of spread to other water bodies.


Alligator weed. Courtesy IFAS K.A. Langeland.

• Alligatorweed is an invasive plant from South America that creates floating tangles of its slick, hollow stems along shorelines, canals, and into Lake Okeechobee. The stems are washed in the color pink and hold oblong leaves opposite each other along their length. Throughout the growing season, alligatorweed produces papery, white flowers in tight, cylindrical heads. Insects released for biological control of alligatorweed keep its growth in check, and sometimes herbicides are needed to manage it.

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