Aquatic Plant Management and Ecological Condition of Florida Springs Questions for Consideration Jason M. Evans Springs Research Symposium University of Florida August 21, 2007

Major Invasive Plants Hydrilla (Hydrilla verticillata) Water hyacinth (Eichhornia crassipes) Water lettuce (Pistia stratiotes)

Wakulla Hydrilla

St. Johns Hyacinth

Ichetucknee Water Lettuce

Other Invasive Plants Eurasian milfoil (Myriophyllum spicatum) Indian Hygrophila (Hygrophila polysperma) Brazilian Elodea (Egeria densa) Giant Salvinia (Salvinia molesta) ?

Control Methods Herbicides –Fluridone (hydrilla, hygrophila, salvinia) Difficult in flowing waters due to long contact requirements Fluridone resistant biotypes Non-target concerns –Endothall (hydrilla, hygrophila) Non-target concerns –2-4,D (hyacinth, hygrophila) Non-target concerns –Glyphosate (hyacinth) Non-target concerns –Diquat (hydrilla, hyacinth, lettuce, salvinia) Non-target concerns –Copper (hydrilla, hyacinth, lettuce, salvinia) Sediment accumulation Manatee toxicity concerns

Other Control Physical –Mechanical harvest Expense Fragment sprouting, particularly hydrilla Non-target concerns –Manual harvest Labor intensive Biological –Grass carp Can over graze native plants –Biocontrol insects Results not immediate Ongoing research and lengthy risk assessments Non-target concerns Perhaps most sustainable over long-term

Question 1 Does increased nutrient (particularly nitrate) loading into Florida springs also increase the spread, growth, and coverage of major invasive plant species?

Question 2 Would decreased nutrient loading lessen the spread, growth, and coverage of invasive plant species?

Question 3 What are the habitat effects of major invasive plants? –Displacement of native plants –Hypothesis that apple snail and limpkin decline in Wakulla directly related to hydrilla invasion –Edge of water hyacinths in St. Marks system found to harbor high densities and diverse assemblages of invertebrates (apple snail, crayfish, amphipods), fish, and wading birds (Bartodziej and Leslie 1998) –Water lettuce and hyacinth preferred habitat for endemic dense hydrobe snail (Aphaostracon pycnum) in Alexander Spring run (Thompson 1968)

Question 4 What, if any, non-target effects are associated with aquatic plant management activities? –Native plant impacts –Deposition of organic matter and “pulsed” nutrient release –Grazer impacts, both toxicological and habitat disruption State of Washington (2003) recently found that diquat can be “highly toxic” to apple snails (Pomacea paludosa) and Hyalella azteca at ecologically relevant dosages (.36 and.07 ppm, respectively) Concerns about crayfish (Procambarus peninsulanus) die-off observed in Wakulla after hydrilla treatment with endothall (Aquathol K) –Algal community composition Opportunistic colonization by algae/cyanobacteria Lyngbya wollei resistant/tolerant to common herbicide formulations

Proposition 1 History of invasive plant colonization and control methods should be directly considered when evaluating the ecological condition of Florida spring systems

Proposition 2 In springs impacted by overgrowth of nuisance algae, careful experimentation with novel aquatic plant management approaches – including tolerance of higher coverage levels by already established invasive plant species – should be explored in conjunction with broader ecosystem rehabilitation and recovery goals