Submerged Aquatic Vegetation Preferences of Fishes in Lake Apopka, Florida

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To achieve the adaptive restoration objective of maximizing fish habitat, researchers will sample fish communities in Florida's Lake Apopka to compare between natural submerged aquatic vegetation (SAV), restored SAV, and bare bottom habitat. To undertand SAV preference of juvenile largemouth bass, researchers will conduct controlled experiments. These experiments will help managers select which plants to use for restoration projects intended to maximize fish habitat in Lake Apopka.

The Science Issue and Relevance: Prior to the 1940’s, Florida’s Lake Apopka was characterized by clear water, dense submerged aquatic vegetation (SAV), and a thriving largemouth bass (Micropterus salmoides) population. However, several environmental stressors, including strong wind uprooting of SAV, land-use change, and nutrient enrichment have altered the system to a less desirable, turbid algal state. Restoring SAV on a large spatial scale has the potential to dramatically improve environmental conditions by stabilizing sediment, increasing water clarity, and assimilating nutrients. Water managers who want to improve the condition of Lake Apopka have prioritized revegetation of this area. However, present environmental conditions in Lake Apopka pose unique challenges to SAV restoration, limiting the efficiency of common approaches, like reintroducing plants. Restoration in this aquatic ecosystem will require innovative methods matched with a careful understanding of environmental stressors.

Adaptive restoration provides a framework for simultaneously and iteratively filling restoration sites in an experimental manner so that lessons learned can be applied more successfully to subsequent, larger restorations. Earlier portions of this project used this framework to answer a series of questions regarding which plant cultivars and which planting techniques would be most effective at restoring SAV in Lake Apopka. In addition to controlled greenhouse experiments, more than 5 acres of SAV are expected to be planted. An additional objective of the project is to enhance overall ecosystem function—like maximizing fish habitat—through the use of SAV plantings.

Potamogeton illinoensis

Illinois pondweed (Potamogeton illinoensis)

(Credit: Anne Murray. Courtesy: Ann Murray. Photo provided by University of Florida.)

Methodology for Addressing the Issue: In order to achieve the adaptive restoration objective of maximizing fish habitat, we will sample fish communities in Lake Apopka to compare between natural SAV, restored SAV, and bare bottom habitat. This will provide broad information about the fish communities that are using the SAV that has already been planted but will not be able to explain which characteristics drive fish habitat preferences. However, controlled laboratory experiments are required to identify specific characteristics of SAV that make for good fish habitat. We can then apply this information to restoration efforts. The largemouth bass was selected for the test species because of its historically high population density in Lake Apopka and its potential contribution to the local economy through tourism and recreational fishing.

To better understand the SAV preferences of juvenile largemouth bass, we will focus on two SAV species: Illinois pondweed, Potamogeton illinoensis and freshwater eelgrass, Vallisneria americana. We will conduct experiments in which we will present individual fish with two to four choices per trial and then compare the time that the fish spend in each of the options to determine preference. Preferences will be tested for: 1) different species of submerged plants, 2) different populations/cultivars, 3) diversity effects (species or genetic), and 4) morphological characteristics of plants (e.g., shoot height/ density).

Micropterus salmoides

Largemouth bass (Micropterus salmoides)

Illustrator: Duane Raver (Public domain.)

Future Steps: Information from the experiments will help managers select which plants to use for restoration projects intended to maximize fish habitat in Lake Apopka. Fish sampling in Lake Apopka may be extended to examine seasonal variation in fish communities in different SAV patches. Experiments may be conducted on other species such as bluegill (Lepomis macrochirus), another desirable fish species, or gizzard shad (Dorosoma cepedianum), an undesirable fish species, to look at the variation in preferences across species. This work will be communicated in reports to the St. John’s River Water Management District, at scientific conferences, and in scientific journals to effectively communicate results to inform future lake restoration efforts.