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
www.jou.ufl.edu/pubs/onb/S05/d_green.html
http://aquat1.ifas.ufl.edu/guide/stboatbg.gif
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