Common Aquatic Plants of Lake Okeechobee: Identification, Value, and Management1 K.A
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SS-AGR-362 Common Aquatic Plants of Lake Okeechobee: Identification, Value, and Management1 K.A. Langeland and C.C. Jacono2 Introduction More information on aquatic plants and their management can be found on http://plants.ifas.ufl.edu. Aquatic and wetland plants are essential to the ecology of Florida lakes, such as Lake Okeechobee, but they can also Types of Aquatic Plants pose ecological and water use problems. Plants provide Aquatic plants are separated into two major groups: 1) food and habitat for sport fish and other wildlife, help im- algae, which are composed of single cells or chains of prove water clarity, and help stabilize shorelines and bottom attached cells, and 2) vascular plants, which usually have sediments. However, certain fast-growing species of plants distinguishable roots, stems, leaves, and flowers (except for can become too abundant, which can be unhealthy for lakes ferns). Vascular plants are described by the way they grow and cause problems for recreational water uses, navigation, and where they occur at different depth gradients in the and flood control. Many plants that are considered a lake: problem to Lake Okeechobee were brought here from other 1. Emersed (or emergent) plants occur along the shoreline parts of the world. When these non-native plants grow out and in the shallower zone. They are rooted to the bottom of control and out-compete native plants, they are referred and grow above the water surface. to as invasive plants. Some plants, especially invasive plants, must be managed on Lake Okeechobee to protect the 2. Submersed plants occur mostly in deeper zones. They health and recreational uses of the lake. Lake Okeechobee are usually rooted to the lake bottom and mostly remain is unique because of its vast size (730 square miles), shallow beneath the water surface. water (9-ft average depth), high nutrient levels, and exten- 3. Floating-leaved plants are rooted to the bottom and have sive marsh (147 square miles), which is heavily used for leaves attached underneath the water. The leaves float on fishing, hunting, and birding. Lake Okeechobee, especially the water surface, with some leaves somewhat emersed. its marsh, is home to numerous plant species that play roles 4. Floating plants are not attached but float freely on the in the lake’s ecology. water surface and can occur anywhere on the lake from This fact sheet provides information about the plants of the shoreline to deep water. Lake Okeechobee and outlines the importance of certain Algae plants to the lake, problems caused by some plants, and the methods used to manage plants for the benefit of the entire Algae can be free-floating single cells in the water (called lake environment. phytoplankton) or stringy and mat-forming (called filamentous algae). Phytoplanktonic algae are usually too 1. This document is SS-AGR-362, one of a series of the Agronomy Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date July 2012. Visit the EDIS website at http://edis.ifas.ufl.edu. 2. K.A. Langeland, professor, Agronomy Department and Center for Aquatic and Invasive Plants; and C.C. Jacono, pest survey specialist, USDA/APHIS/ PPQ, Gainesville, FL; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611. The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A&M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Thomas A. Obreza, Interim Dean small to see as individuals, but their presence causes water preventing exchange of water. They can also block boating to appear green or sometimes brown. access and cause narrowing of boat channels, creating a Phytoplankton is important to lakes because it provides boating hazard. Lake Okeechobee’s most common emersed food for small organisms, which in turn produce food for plants are described below as found from shoreline to larger animals such as fish and waterfowl. Phytoplanktonic deeper water. algae are also important because they produce oxygen Arrowheads in the water, which is necessary for fish to breathe. The Arrowheads are hefty shoreline plants that hold their amount of phytoplankton in a lake is related to the fertility large leaves upright on sturdy leaf stalks, which become of water. Highly fertile water contains high amounts very spongy at the base. They produce flowering stalks of the plant nutrients, nitrogen and phosphorus. It can summer-round that hold flowers in a series of whorls along produce more phytoplankton than less fertile water and, the upper portions. Three white petals make up each flower, in turn, larger and greater quantities of fish can grow. Lake which appear as light and thin as paper confetti surround- Okeechobee is naturally fertile, producing large amounts of ing a central yellow disk. The bulltongue arrowhead is phytoplankton, and has an excellent fishery. named for the long, elliptic shape of its upward-pointing Excessive amounts of phytoplankton, called blooms, some- leaves. Like the other arrowheads, the bulltongue persists times occur. When blooms occur during hot weather and through the changing wet and dry conditions that occur are followed by several days of cloudy cover, large amounts along Lake Okeechobee’s shoreline. Broadleaf arrowhead of phytoplankton can die and the result is a depletion of differs from the bulltongue by its triangular lobes at the oxygen in the water, sometimes followed by death of fish. These natural “fish-kills” have always occurred in shallow, warm-water southern lakes. There is concern over larger and more frequent phyto- plankton blooms in Lake Okeechobee. There is even greater concern for these blooms because they are composed of a type of algae known as blue-green algae (cyanobacteria), which produces chemicals in the water that are toxic to fish. It is believed these blue-green algae blooms are related to elevated fertility in Lake Okeechobee water caused by runoff from urban areas that drain into the Kissimmee River, from farming practices and nutrients already in the lake sediments, re-suspended into the water after high- wind events. Several species of blue-green algae can utilize nitrogen from the air and therefore bloom even when nitrogen levels in the water are low. Efforts by the South Figure 1. Bulltongue arrowhead. Credits: Vic Ramey, http://plants.ifas. Florida Water Management District (SFWMD) and the ufl.edu U.S. Army Corps of Engineers (US COE) are under way to correct these problems. Emersed Plants Emersed plants are the most evident vegetation on Lake Okeechobee. The underwater portions of emergent plants provide refuge for small animals, which are forage for game fish such as largemouth bass. The upper portions of taller emergent plants such as bulrushes and cattails are used for nesting birds such as flycatchers and the endangered snail kite. Birds eat the seeds produced by bulrushes, smartweed, and aquatic grasses. Emersed plants are also important for protecting near-shore areas from wave action. However, emersed plants, particularly cattails, can become so thick that they cause stagnant conditions in backwater areas by Figure 2. Broadleaf arrowhead. Credits: KAL 2 Figure 3. Maidencane. Credits: Vic Ramey, http://plants.ifas.ufl.edu Figure 5. Southern amaranth. Credits: Ann Murray, http://plants.ifas. ufl.edu though not plentiful, are nutritious. Where it moves into deeper waters that lack a firm mineral bed, maidencane can be used as nest substrate by largemouth bass. Unfortunately, this important plant disappears if seasonal fluctuations are eliminated, such as when water levels are permanently increased, stabilized, or lowered. Spikerush Spikerush (also called needlegrass) isn’t a rush or a grass, Figure 4. Spikerush. Credits: David Sutton but a sedge that grows like a field of olive-colored straw leaning this way and that in the shallow marsh. Its stems are base of the leaf, resulting in a leaf shaped like the broad circular and grow to 30 in. in height. The tips of the stems point of an arrow. develop minute braided rows of flowers that mature and dry into tan seed heads. Spikerush plants have underground Maidencane stems that spread through the lake bottom, producing many Maidencane is an important native aquatic grass that round tubers as they grow. Spikerush fields are excellent stretches along the coastal plain from New Jersey to duck habitat, offering a thick, camouflaged cover and food southern Florida. Its leaves are wider and flatter than in the form of both tubers and seeds. The Florida mottled torpedograss, with edges that feel scratchy to the touch and duck, a non-migratory mallard, is especially known to eat taper toward the tip. The plants are larger and the stems its seed. grow taller and more upright than torpedograss, and the leaves are held at a wider angle from the stem. Maidencane Southern Amaranth forms the backbone of the wet prairies inhabited by the Southern amaranth (also called giant pigweed) is a fast- Florida panther, offers prime forage for deer, and creates growing giant of the marsh that returns from seed every upright habitat in the shallow marshes, ponds, and shore- spring on high mounds along shorelines that dry down or lines of Lake Okeechobee. Maidencane is a paradise for the on levees around Lake Okeechobee. Southern amaranth insects, small reptiles, and fish that support wading bird has lance-shaped leaves on stalks that attach to the mas- populations.