Submerged Aquatic Vegetation Control
Three of the most troublesome aquatic plants in local waters are Lyngbya sp., a cyanobacteriaBacteria that have the ability to photosynthesize.
algae, Eurasian water-milfoil, Myriophyllum spicatum, and Hydrilla, Hydrilla
verticillata. Lyngbya is discussed under AlgaeAny of various chiefly aquatic, eukaryotic or bacterial, photosynthetic organisms, ranging in size from single-celled forms to the giant kelp. Algae were once considered to be plants but are now classified separately because they lack true roots, stems, leaves, and embryos.
in the Education Section and under Algae Control in
the Conserve and Restore section. The following commentary is based upon
text of Ken Langeland in the booklet: Hydrilla
verticillata: The Perfect Aquatic Weed.
Eurasian Watermilfoill was introduced to the United states unintentionally in the 1950s, and has
since spread throughout the nation. It grows in lakes and rivers forming dense mats on the surface
to severely restrict the use of the waters. It is fragile, and stems broken by boat propellers,
passage of personal watercraft and mechanical harvesters, sprout roots to promote new growth from
each small fragment.
Eurasian Watermilfoil is now prohibited by law from being owned or transported in the United
Hydrilla was brought to the United States for sale as an aquarium decoration in the 1950s from
Asia. It was planted in lakes and canals for harvest and sale through pet shops. It grows from
submersed corms and when it reaches the surface hydrilla grows across the surface to form dense
tangled mats, impeding boat traffic and causing flooding by jamming against bridges and blocking
New plants sprout from broken stems or root buds (tubers). It is now prohibited by law from being
owned or transported in the United States.
How they spread from place to place
Each is spread from one water body to another as fragments attached to boats, trailers or
vehicles or attached to wildlife, and transported by water currents. Now, almost every state
suffers from infestations, and yet these invasive speciesA taxonomic category subordinate to a genus (or subgenus) and superior to a subspecies or variety, composed of individuals possessing common characters distinguishing them from other categories of individuals of the same taxonomic level.
In taxonomic nomenclature, species are designated by the genus name followed by a Latin or Latinized adjective or noun.
continue to be sold through aquarium supply dealers and on the Internet.
In a water body such as Crystal River/Kings Bay, they are particularly spread by being chopped by
The Damage They Do
These invasive plant species cause major detrimental impacts upon water use. In drainage canals
they greatly reduces flow, which can result in flooding and damage to canal banks and structures. In
irrigation canals they impede flow and clog pump intakes used for conveying irrigation water. In
utility cooling reservoirsA natural or artificial pond or lake used for the storage and regulation of water. they disrupt
flow patterns that are necessary for adequate cooling of water. They can severely interfere with
navigation of both recreational and commercial craft. In addition to interfering with boating by
fisherman and water skiers in recreational waters, they interfere with swimming, shade out and
displace native vegetation communities, and can adversely impact sport fish populations. Decaying
plant material reduces dissolved oxygenMeasures the amount of gaseous oxygen dissolved in an aqueous solution. Oxygen gets into water by diffusion from the surrounding air, by aeration (rapid movement), and as a waste product of photosynthesis. levels. Birds and fish are adversely affected as their feedstock becomes less accessible.
The economic impacts of such damage upon real estate values, tourism, and user groups can be
staggering. For example, an economic study on Orange Lake in North Central Florida indicated that
the economic activity attributed to the lake was almost $11.0 million and during years that hydrilla
completely covers the lake these benefits can be virtually lost (Milon et al. 1986). Cost
of invasive plant management is also extremely high, especially when funding is insufficient for
adequate management. An estimated $10.0 million is necessary to manage hydrilla alone in Florida
public waters in 1994-95 and $14.5 million was necessary in 1995-96, as infestations continued to
The Good They Do
Before migrating to richer pasture, it has been reported anecdotally, that manatees feed on the
milfoil to last them on their journey. In the absence of natural feedstock, for example eelgrassA marine plant with long ribbon-like leaves. [Zostera marina.], or, a submerged aquatic plant with narrow, grass-like leaves. [Genus Valisneria.]
and nyad, the manatees will feed on hydrilla.
Some sport fishermen consider hydrilla to benefit largemouth bass habitat (Tucker 1987). While
the opinion that hydrilla is beneficial for sport fish production is supported by certain research (Estes
et al. 1990; Porak et al. 1990), other research suggests that largemouth bass are
adversely affected when hydrilla coverage exceeds 30% (Colle and Shireman 1980). Canfield and Hoyer
(1992) found no relation between standing crop of harvestable largemouth bass and percent area
covered with aquatic macrophytes in 60 Florida lakes (many dominated by hydrilla).
Clear water is valued by the public and large populations of submersed aquatic macrophytes, such
as hydrilla, will tend to increase water clarity (Canfield et al. 1984). The exact reasons
for this increase in water clarity are not completely understood but it probably results from a
combination of factors which include reducing sediment resuspensionThe suspension of particles in the water column after having once been settled and disturbed. and reduction of phytoplanktonSmall photosynthetic organisms, mostly algae and bacteria, found inhabiting aquatic ecosystems. Also see plankton and zooplankton.
populations by compartmentalizing nutrientsAny food, chemical element or compound an organism requires to live, grow, or reproduce..
Regardless, very large amounts of aquatic macrophytes would be necessary to cause substantial
increases in water clarity (Canfield et al. 1984; Canfield and Hoyer 1992).
Hydrilla is eaten by waterfowl, and maintaining hydrilla populations is sometimes advocated by
waterfowl scientists because it increases the feeding habitatThe place or set of environmental conditions in which a particular organism lives.
for ducks (Johnson and Montalbano 1984, Esler 1989). Attempts to benefit sport fish or waterfowl
habitat, or produce clearer water has led to deliberate dispersal of hydrilla by individuals unwary
of the severe detrimental impacts that can be caused by these plants.
Obviously, the use of mechanical harvestersFloating machinery driven by paddlewheels for lifting algae and plants from a water body and transporting them for disposal risks leaving chopped residuesWhat is left over or remains; the part of a molecule that remains after portion of its constituents are removed. Residues of some contaminants may remain after
behind to grow again more densely than before. The literature describes draw down of the water in
lakes and ponds to access and remove the plants, but this is of little use in a river run. Herbicides
are effective but result in ecologic shock when applied over larger areas, and harmful residues of
muck accumulate in sedimentsSolid material that has been or is being eroded, transported, and deposited. Transport can be due to fluvial, marine, glacial or aeolian agents., allowing
persistent bioaccumulative toxins to occur.
Detriments caused by water-milfoil and hydrilla far outweigh benefits and they are usually more
difficult to manage than native plant populations which they displace. It seems clear that before water qualityA term used to describe the chemical, physical, and biological characteristics of water, usually in respect to its suitability for a particular purpose. restoration can be undertaken effectively, some method of isolation and removal of these
plants should be determined, so that progressive replacement by native plants can take place.
It is well understood that SAV take nutrient from the biomass in which they may be rooted, and
from the water column, while utilizing energy from the sun.
Moreover, tidal levels vary according to the direction from where the wind is blowing and its
strength which is not subject to any consistent repeating pattern. The angle subtended by the sun
influences how much energy is available for use at the depth the nascent SAV or algae lay below the
water surface. The depth of water is not predictable as it is the consequence of diverse global
Moreover, reduced rates of flow of spring discharges not only results in increased sedimentation
in up-stream flow pathways which further reduces flow rates, but also in increased nutrient
concentrations in the discharge water. This appears to stakeholders to reduce current levels would
result in further degradation when increased spring flow would be required as also recommend in FGS
Bulletin 69 as indicated below.
The following local observations are example of the effects of the phenomena.
Prior to 2006 some small amount of chaetomorpha were reported to existed in Kings Bay. Fresher
water species such as Lyngbya Wollei and enteromorpha had exploded to predominate as algae. SAV
species such as Vallisnaria and Coontail had been largely displaced by Asian Water Milfoil.
However, in the third week of March 2006, massive vigorous blooms of chaetomorpha were observed
which suppressed the traditional Lyngbya blooms due a month or so later. At the time of the
chaetomorpha blooms we had experienced extremely low tides and although the sun was at an acute
angle it was nevertheless sufficient to energize the blooms. The event coincided with high salinity
levels in the spring discharge from Black Spring and the associated vents in Kings Creek mainly due
to the long period of drought but also from excessive pumping along the path of the aquifer SE-NW
trended tributary. (Albeit, we did not have any confirmation of any tributary until the later
Hopkins Hopkins study).
Similar events occurred in 2007, 2008 and 2009. However, heavier rains in late 2009 extending
into 2010 reduced the salinity levels in discharges from Black Spring and Tarpon Spring by more
than half. Although sufficient to significantly modify salinity levels, note that the increased
rainfall was less than that of an average year. Behavior of SAV and algal species changed in 2011.
The chaetomorpha bloomed earlier in 2011 but was not sustained nor was it so vigorous as in the
prior years. The weather pattern changed allowing the Lyngbya and enteromorpha to bloom. With the
present day result that chaetomorpha is on the bottom with Lyngbya and enteromorpha on the surface
in several areas. This was mentioned in course of my report to the CHWRC-Task Force in the presence
of TAG members on 14 March, 2011, illustrating the sensitivity of the degraded waters of Crystal
The April, 2011, readings of specific conductance in the Black Spring discharge was measured at
12,220 units - approaching the previous high levels. It is also well reported that Lyngbya requires
a cocktail of nutrients and blooms and toxicity are subject to accelerators in the cocktail such as
molybdenum and other trace elements probably arising from road traffic run off. (This has not yet
been mentioned with regard to the Tarmac Kings Road mine representations against the proposed US 19
daily transit of 1000 heavy trucks ).