Conservation Biology Class
Stetson University
Fall 2011
Proposal to reintroduce eelgrass (Vallisneria americana) into Volusia Blue Spring
Species introductions are now recognized as one of the most important ways by which
humans affect ecosystems, both positively and negatively, and this species of eelgrass would
benefit the ecosystem within Blue Spring for many reasons (Strayer, 2003). Introduction of
Vallisnera americana into Blue Spring would allow for a new and abundant habitat for
invertebrates. Eelgrass offers food, shelter, and essential nursery areas to many species that are
produced within, or migrate to, eelgrass. Vallisneria americana produces tall leaves that provide
refuge for juvenile fish, small species of finfish, and benthic invertebrates (e.g. amphipods, insect
larvae, snails) (Hill, 2002).
In addition to the protective features of eelgrass, it also serves to dampen the effects of
strong currents for fish and invertebrates, while also preventing scouring of bottom areas. These
epiphytic organisms are important contributors to the food webs in their ecosystem. Organisms
graze on the eelgrass directly, such as manatees (Trichechus manatus) and cooters (Pseudemys
sp.), and the death of the epiphytes provides a detrital carbon source to the food web (Hill, 2002).
Reproduction and Life Cycle
Vallisnera americana is a dioecious, perennial, aquatic macrophyte. It is stoloniferous
and capable of extensive clonal growth; most individuals in a population remain vegetative. The
female flowers of the plant remain attached to the parent plant by a long spiral peduncle (Fig. 1)
and male inflorescences, containing many minute flowers (Fig. 2), open their sheaths and release
their flowers as small "boats" which rise to the surface. Male flowers are left to float on the water
due to surface tension riding water currents. Pollen is kept dry through this process and
pollination is effected by wave action which moves male flowers to contact female flowers and
pollination takes place (Doust, 1991).
Due to the way the flowers are pollinated, we would recommend having at least one
population of eelgrass near the boil but not in the boil. This strategy should maximize
reproductive potential; when plants begin to flower the slow movement of the water from the
boil to the river should carry along the male flowers and hopefully pollinate those female flowers
that are down the run as well as possibly pollinate those near the boil.
Vallisneria americana begins rapid growth around June. By mid-summer, the
aboveground biomass in most ecosystems has reached its peak and growth slows somewhat in
response to higher water temperature; however, Blue Spring has a consistent temperature year
round, so there will be less variability in growth rates. During winter, growth is slowed
considerably. On average, individual shoots of eelgrass do not live for more than two years.
(Cornell, 2010)
Figure 1. A female flower of Vallisneria americana.
Figure 2. Male flowers surrounding a female flower of
Vallisneria americana.
http://www.aquaticplantcentral.com/forumapc/aquascaping/58638my-124g-planted-tank-4.html
http://www.plantsystematics.org/imgs/kcn2/r/Hydrocharitaceae_Vall
isneria_americana_15816.html
Habitat
Vallisneria americana requires certain conditions to maximize survival and reproduction,
such as specific depth requirements, substrate composition, thermal requirements, and sufficient
light exposure. The depth requirement for V. americana ranges between 0.2 meters and 3 meters
(Korshgen and Green, 2006). Vallisneria americana tubers can be observed in the wild at depths
from 10 to 20 cm in silty clay substrate and at depths of 5 to 15 cm in sand (Rybicki and Carter,
1986). Under laboratory conditions, survival of planted seeds was 90% when burial depth was 10
cm or less, but seed mortality was 100% when they were buried in substrate 25 cm or greater
(Rybicki and Carter, 1986). Jarvis and Moore (2008) found that sediment composition of ≤ 3%
organic content and > 40% sand enhanced the germination and growth of V. americana seeds
under laboratory conditions. Overall, however, there exists considerable variability in the
sediment composition that supports growth and reproduction for V. americana.
The recommended light requirements for V. americana range between 20.4 - 78.3 µmol
m-2s-1 for maximum photosynthetic rates (Boustany et al., 2010). Between these two extremes,
V. americana reproduces at an increasing rate (Kurtz et al., 2003). The thermal requirements for
V. americana are relatively distinct. In water temperatures below 20°C, growth is severely
restricted. In water temperatures above 50°C, plants become limp and disintegrate. Therefore, the
ideal temperature range is between 20°C and 36°C (68°F - 96.8°F) (Korshgen and Green, 2006).
Blue spring meets these temperature requirements by remaining 22oC (72°F) throughout the year
(Scott et al., 2002).
Potential threats to the restoration
Volusia Blue Spring contains threats to the success of project. The biggest threat to V.
americana that is present in the spring is the manatee. A manatee can eat from six to eight hours
a day (Van Meter, 1989) and sea grass cores taken in grazed and ungrazed areas of Hobe Sound,
FL, indicated that manatees can reduce shoot densities to half the density of ungrazed sea grass
beds (Lefebvre et al. 2000). Volusia Blue Spring hosts large numbers of manatees in the colder
months due to the constant temperature of the spring (Wetlands Solutions, Inc., 2009). Grass
carp (Ctenopharyngodon idella) and turtles also pose a threat to V. Americana in the spring.
Grass carp have been known to eat eelgrass and they can eat as much as 25% of their body
weight per day, at least for hydrilla, Hydrilla verticillata (Shireman and Maceina 1981).
Pseudemys sp. (cooters) strictly feed on aquatic vegetation, unlike the other turtles in that occur
in the spring (Wetlands Solutions, Inc., 2009; Bjorndal et al. 1997). Although their diet is strictly
herbivorous, depending on the season or drought conditions, they can go days, weeks, or months
without eating (Buhlmann et al., 2008). Red eared sliders (Trachemys scripta elegans) also will
eat aquatic vegetation such as V. americana, although it is not their preferred diet. They
primarily feed on small fish, insects and tadpoles (Cagle, 1950). These turtles may not be a big
threat, but they can cause damage to the restoration project depending on the condition of the
spring.
Volusia Blue Spring is a big attraction to tourists, and the presence of large numbers of
tourists (average = 812 visitors day-1, range = 0 - 6140 visitors day-1, Wetlands Solutions, 2006)
is another possible threat to V. americana. High traffic areas in the run may prevent V.
americana from growing. Visitors are unaware of the impact they have on the delicate vegetation
that is present. Since V. americana would have to be present along the bank areas, tourists will
have to be informed not to climb or brush against those areas to preserve the restoration efforts.
Scale of Reintroduction
We support the attempt at V. americana restoration in Volusia Blue Spring, but if the
initial attempts are unsuccessful, we would advise forgoing the continuation of the reintroduction
in Volusia Blue Spring run. Based on available funding, we propose two options. One, we
suggest small scale tests on three sites mentioned later in proposal, to determine propagation and
success of V. americana. If such attempts prove to be successful in any of the three sites, then we
recommend continuation on the successful sites of the restoration effort on a larger scale. A
second option would be to forgo small-scale tests and do a full-scale restoration of V. americana
at the three sites (again mentioned later in this proposal). If initial test sites fail or the full
restoration fails, we advise that this restoration project be put on hold or dismissed in favor of
other restoration activity needed in Blue Spring State Park.
Restoration Strategy
A strong strategy for re-establishing V. americana into Volusia Blue Spring will be to
establish small founder colonies. By focusing on excluding herbivores and allowing time for the
new beds to establish themselves, these initial founder beds may well serve as a source for
natural population establishment throughout the spring (Dick and Smart, 1999). These initial
colonies should consist of transplanted mature individuals; seeds in Vallisneria tend to germinate
less well than adult plants when implanted in sediment (Ke and Li, 2006) and with the flowing
current of Volusia Blue Spring, we would expect free floating seeds to have a very low chance of
implanting in the sediment. As manatees pose the largest threat to these initial colonies, strong
enclosures mounted at strategic times of the year will be vital. Mortality rates in V. americana
colonies exposed to manatee herbivory in Kings Bay Florida were 100% for recently planted
propagules; the manatees were apt to tear out all parts of the plant. However in established beds,
manatees tended to graze on above ground foliage while leaving the plant intact in the sediment
(Hauxwell and Osenburg, 2004). Hauxwell and Osenburg (2004) also suggested that survival of
colonies was highly variable and that the most effective restoration strategies will establish
multiple sites for founder colony implantation. This strategy allows for a higher chance that
colonies will experience favorable site-specific factors like low competition and herbivory, and
favorable light, sediment, and disturbance conditions (Hauxwell et al., 2004)
Based on the suggestions of previous restoration studies of V. Americana, we suggest the
following strategy. At least three colonies should be planted: one just upstream from the small
spring inlet, one in the area downstream of the swim dock, and one across from the swim dock
(Fig. 3). This separation of colonies will allow, if the plants become established, for higher
reproductive success as flowers can flow downstream to other patches for fertilization.
Enclosures should be constructed from simple materials. We suggest 1.5 m2 enclosures. We
suggest utilizing four agricultural T-posts driven into the substrate at the corners of a 1.5m2
square, wrapped with galvanized steel agricultural fencing (approximately 20ft of fencing per
enclosure). The height of the T-posts and the fencing used will vary with water depth, but the
posts should be driven deeply into the substrate as to minimize the chance of any damage that
may be inflicted by passing manatees. The fencing should be fixed to the T-posts using heavy
duty T-post clips. The spacing of the mesh in the fencing should not exceed 2x3 inches in order
to exclude other herbivorous species, besides manatees, that may graze upon the propagules.
These enclosures should contain of at least 50-100 propagules each. The propagules should be
adult transplants, not seeds. Ideally, transplants should come from a local source, such as the
Wekiwa River, Rock Spring, or perhaps even the St. Johns River near Blue Spring. Maintaining
genetic diversity is usually one of the goals of macrophyte restoration (Fonseca et al., 1998;
Williams and Orth, 1998; Rhode and Duffy, 2004), so we encourage collection of material from
multiple sites. The individuals should be planted 10-20 cm deep and immediately surrounded by
enclosures. These colonies should be established during the summer, in July for optimum light
exposure.
Diver entry
Potential
restoration
sites
Swim dock
Second to last
observation platform
Figure 3. Map of Volusia Blue Spring showing potential restoration sites for V. Americana.
Monitoring
Once the V. americana restoration has been implemented, it will be necessary to monitor
the population(s). A count of the initial number V. americana sprigs and repeated counts of the
number of sprigs every month would allow managers to track population changes. This
monitoring should be done until managers can conclude that the population is viable and that the
V. americana restoration has been successful. If it seems the restoration is a success, monitoring
can be extended to every two months, then every three months, etc. If it seems that the
restoration is not working, depending on the severity of population decline, it may be best to
change the approach of restoration or abandon the project all together. Furthermore, if the
populations are declining, it would be beneficial to know why – whether it is due to predation, or
insufficient habitat conditions. Possibly, these conditions can be adjusted to benefit the V.
americana.
Literature cited
Boustany RG, Michot TC, Moss RF. 2010. Effects of salinity and light on biomass and growth of
Vallisneria americana from lower St. Johns River, FL, USA. Wetlands Ecology Management 18:
203-217.
Bjorndal, KA, Bolten, AB, Lagueux CJ, Jackson, DR. Dietary overlap in three sympatric congeneric
freshwater turtles (Pseudomys) in Florida. Chelonian Conservation and Biology 2(3): 430-433.
Buhlmann K, Tuberville T, Gibbons, JW. 2008 “Turtles of the Southeast”. University of Georgia Press.
1-249
Cagle, FR. 1950. “The Life History of the Slider Turtle, Pseudemys scripta troostii (Holbrook)”
Ecological Society of America. Vol. 20(1): 31-54.
Doust JL, Laporte G. Population Sex Ratios, Population Mixtures and Fecundity in a Clonal Dioecious
Macrophyte, Vallisneria americana. Journal of Ecology 1991. 79: 477-489
Hauxwell J, Frazer TK, Osenberg, C.W. An annual cycle of biomass and productivity of Vallisneria
americana in a subtropical spring-fed estuary. Aquatic Botany 2007. 87(1): 61-68
Hauxwell J, Frazer TK, Osenberg CW. 2004. Grazing by Manatees Excludes Both New and Established
Wild Celery Transplants: Implications for Restoration in Kings Bay, FL, USA. Journal of Aquatic
Plant Management. 42: 49-53
Hauxwell J, Osenberg CW, Frazer, TK. 2004. Conflicting Management Goals: Manatees and Invasive
Competitors Inhibit Restoration of a Native Macrophyte. Ecological Applications. 14:2, 571-586.
http://www.jstor.org/stable/4493559
Hill K. (2002, June 28). Segrass Habitats. Retrieved September 22, 2011, from Smithsonian Marine
Station at Forst Pierce: http://www.sms.si.edu/irlspec/seagrass_habitat.htm
Jarvis JC, Moore KA. 2008. Influence of environmental factors on Vallisneria americana seed
germination. Aquatic Botany 88: 283-294.
Korshgen C, Green W. 2006. American Wildcelery (Vallisneria americana): Ecological Considerations
for Restoration: Ecology. [Online]. Available from:
http://www.npwrc.usgs.gov/resource/plants/wildcel/ecology.htm. Accessed 2011 Sept 25.
Kurtz JC, Yates DF, Macauley JM, Quarles RL, Genthner FJ, Chancy CA, Devereux R. 2003. Effects of
light reduction on growth of the submerged macrophyte Vallisneria americana and the
community of root-associated heterotrophic bacteria. Journal of Experimental Marine Biology
and Ecology 291: 199-218.
Lefebvre L, Reid JP, Kenworthy WJ, Powell, JA. 2000. Characterizing manatee habitat use and seagrass
grazing in Florida and Puerto Rico: implications for conservation and management. Pacific
Conservation Biology 5: 289-298.
McFarland DG. 2006. Reproductive Ecology of Vallisneria americana Michaux. Army Core of Engineers.
Report ERDC/TN SAV-06-4.
Rybicki NB, Carter, V. 1986. Effect of sediment type on the survival of Vallisneria americanaMichx
grown from tubers. Aquatic Botany 24: 233-240
Scott TM, Means GH, Means RC, Meegan, RP. 2002. First Magnitude Springs of Florida. 85.
Tallahasse, FL. 125. Print.
Shireman JV, Maceina MJ. 1981. The utilization of grass carp, Ctenopharyngodon idella Val., for
hydrilla control in Lake Baldwin, Florida. J. Fish Biology 19(6): 629-636.
Smart RM, Dick GO. Propagation and Establishment of Aquatic Plants: A Handbook for Ecosystem
Restoration Projects. Aquatic Plant Control Research Program.Technical Report A-994.February,1999. US Army Corps of Engineers Waterway Experiment Station.
http://www.globalrestorationnetwork.org/wp-content/uploads/cipm_pdfs/res%201037.pdf
Van Meter, V. 1989 “The Florida Manatee.” Florida Power & Light Company. 1-41.
Wetland Solutions, Inc. 2006. Human Use and Ecological Evalution of the Recommended
Minimum Flow Regime for Blue Spring and Blue Spring Run, Volusia County, Florida.
Final Report to St. Johns River Water Management District.
Wetland Solutions, Inc. 2010. Water Resource Value Monitoring for Blue Spring and Blue
Spring run, Volusia County, Florida: Final Report. St. Johns River Water Management
District, Special Publication SJ2010-SP5.