FNAI Global Rank: G2

FNAI State Rank: S2

Federally Listed Species in S. FL: 11

State Listed Species in S. FL: 26

Seagrasses are submerged vascular plants that can

form dense vegetative communities in shallow water

estuaries. Though not true grasses, these grass-like

plants are termed seagrasses because they grow in highly

variable salinity environments. Seagrasses are unique in

that they carry out their entire life cycle completely

submerged in salt water. Worldwide, there are more than 50

species capable of inhabiting this submerged environment,

a relatively small number compared with the number of

plant species in other environments. In South Florida,

seven species of seagrass presently occur throughout this

regions estuaries.

Seagrasses are a highly productive, faunally rich, and

ecologically important habitat within the coastal lagoons

and estuaries of South Florida. In terms of primary

productivity, a seagrass bed can produce four to ten times

the weight of organic matter as that produced by a cultivated

corn field of the same size. Vast, extensive seagrass beds

covering hundreds of kilometers may be composed of one

to maybe four species. Yet, hundreds to thousands of species

of flora and fauna may inhabit these beds, utilizing the food,

substrate, and shelter provided by these submerged plants.

Rapidly growing seagrass leaves provide food for

trophically higher organisms via direct herbivory or from

the detrital food web; the canopy structure formed by these

leaves offers shelter and protection. This combination of

shelter and food availability results in seagrass beds being

the richest nursery grounds in South Floridas shallow

coastal waters. As such, many commercial and recreational

fisheries (e.g., clams, shrimp, lobster, fish) are associated

with seagrass beds.

Seagrasses have experienced declines in abundance

and distribution due to water quality degradation and

through the direct loss of habitat related to dredge and fill

activities (e.g., navigation channels, marinas) and boating

impacts (e.g., propeller scars and groundings). The

degradation of water quality is largely the result of point

source pollution (e.g., wastewater discharge, agricultural

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Turtle grass (Thalassia testudinum) Photograph

courtesy of Florida Department of Environmental

Seagrasses
runoff, excessive freshwater discharge), nonpoint source pollution (e.g.,

stormwater runoff, leaching from septic tanks), and the alteration of adjacent

watersheds. The subsequent decline in seagrasses has significantly reduced the

fisheries resources in South Florida.

Implementation of several protective and restorative measures has

improved water quality and radically reduced the rate of habitat loss within

South Floridas estuaries. Such measures include the regulation of dredge and

fill activities, the elimination of wastewater discharge to surface waters, the

treatment of stormwater runoff, and the rehabilitation of adjacent watersheds.

Other significant actions include the establishment of management entities

designed to preserve and protect biologically unique areas.

Synonymy

Seagrasses are also referred to as submerged aquatic vegetation and

macrophytes, terms that may include both attached and drift macroalgae.

FLUCCS codes for the seagrass community include: 510 (stream/waterways),

540 (bays/estuaries), 651 (tidal flats), and 652 (shorelines).

Distribution

Three seagrass species commonly occur in varying degrees of abundance

throughout South Floridas coastal ecosystem: turtle grass (Thalassia

testudinum), manatee grass (Syringodium filiforme), and shoal grass (Halodule

wrightii) (Zieman 1982). Three other species of seagrass are sparsely

distributed within this range: star grass (Halophila engelmannii), paddle grass

(Halophila decipiens), and Johnsons seagrass (Halophila johnsonii). In areas

of reduced salinity, widgeon grass (Ruppia maritima) is often found intermixed

with shoal grass. Unlike the other seagrasses, widgeon grass is actually a fresh

water plant that has a pronounced salinity tolerance. Hence, its occurrence in

estuaries with lowered salinities is commonplace.

The geographic distribution of seagrasses occurs in most of the coastal

counties of Florida (Figure 1) (Zieman 1982, Zieman and Zieman 1989). The

greatest abundance of seagrasses in the region is in an area that includes

Florida Bay and the Florida Keys with approximately 587,770 ha (Sargent et

al. 1995). The second largest seagrass bed (> 300,000 ha) occurs along the

northwest Floridas Big Bend region, an area that extends from north of Tampa

Bay to Apalachee Bay in the Florida panhandle (Livingston 1990). Seagrasses

extend north of South Florida inshore of barrier islands along both coasts and

are found within lagoonal systems, such as Sarasota Bay, Charlotte Harbor,

Biscayne Bay, Lake Worth Lagoon, and the Indian River Lagoon. All seven

seagrass species that are present in this region are found throughout this range.

Turtle grass is most abundant in the Florida Keys and Florida Bay whereas

shoal grass and manatee grass are more predominant along both coasts north of

Monroe County. The lone exception is Johnsons seagrass, the distribution of

which is limited to the east coast of Florida from Sebastian Inlet (Indian River

County) to northern Biscayne Bay (Miami-Dade County). Relative to the other

six species, Johnsons seagrass comprises less than one percent of the total

abundance of seagrasses within its range (Kenworthy 1997).

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SEAGRASSES Multi-Species Recovery Plan for South Florida
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SEAGRASSES Multi-Species Recovery Plan for South Florida

Figure 1. The distribution of seagrasses in South Florida (data from Florida Department of

Environmental Protection).
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SEAGRASSES Multi-Species Recovery Plan for South Florida

The vertical distribution of seagrasses is controlled primarily by interactions

between light availability and wave action and, secondarily, by substrate type and

nutrient supply (Day et al. 1989). Seagrasses can influence the nature and depth

of their own sediment bed by trapping and binding sediment particulates

associated with damping wave and tidal energy (Burrell and Schubel 1977). Their

physical structure stabilizes sediments and prevents the resuspension of

particulate matter, thus helping to maintain water transparency or clarity

(Kenworthy and Haunert 1991). Seagrass beds are often associated with substrate

composed of a thick layer of highly sorted, fine-grained sediments. The density of

seagrasses is typically greater where there is a reduction in wave action and ample

nutrients are available in the sediments, although dense seagrass beds can occur in

high-energy environments with sandy sediments.

Description

Seagrasses are vascular plants that can form dense vegetative communities in

shallow water estuaries (Day et al. 1989). These plants have evolved the ability to

carry out their entire life cycle completely submerged in the marine environment.

Structure and Composition

A remarkable similarity of vegetative appearance, growth, and morphology exists

among the seagrasses. They have a linear form exhibited by a root system

(rhizomes and roots) below ground and leaf structure (short shoots and leaf

blades) above ground. Turtle grass, manatee grass, shoal grass, and widgeon grass

are similar in appearance in that their leaves are long and either cylindrical (i.e.,

manatee grass) or flat. The flat blades are either broad (i.e., turtle grass) or narrow.

The Halophila species differ from the other seagrasses in that the leaf structure is

shorter with the blades resembling tufts or whorls.

Turtle grass is the largest and most robust of South Floridas seagrasses;

Johnsons seagrass the most diminutive. Manatee grass is distinctive in having

cylindrical leaves which are quite brittle and buoyant. As seagrass blades break

off, they are exported from the immediate area by winds and currents. Shoal grass

is recognized as the pioneer species in the successional development of seagrass

beds.

For all the Florida seagrass species, the leaf structure emanates vertically from

the horizontal rhizomes at regular intervals. From the rhizomes, which are just

under the sediment surface, emerge the roots and root hairs into the surrounding

substrate. Seagrass rhizomes range in diameter from 1 mm (0.04 in) for the

Halophila group to 1 cm (0.4 in) for turtle grass. These plant components form a

well-developed anchoring system and constitute the below-ground biomass of the

plant. The leaf structure consists of short shoots from which leaf blades emerge

into the water column. Leaf blades from these species range in width from 1 mm

to 1 cm (0.04 to 0.4 in) and in length from 5 mm to 1 m (0.2 to 40 in). The leaf

varies in shape for the Halophila group from oval to linear while the other species

are essentially elongate. These components represent the aboveground biomass or

standing crop of the plant.
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SEAGRASSES Multi-Species Recovery Plan for South Florida

Seagrass biomass consists of the weight of all living plant material (e.g.,

roots, rhizomes, leaf structure) and is expressed in terms of mass per unit area.

Seagrass biomass and the standing crop of seagrass beds are terms used to

quantify the density of seagrasses. The majority of seagrass biomass is usually

below the sediment surface. The robust root and rhizome system of turtle grass

contains between 55 and 90 percent of the plants total biomass (Zieman and

Zieman 1989). Despite shallower, less well-developed roots and rhizomes,

both manatee grass and shoal grass have a greater portion of their total biomass

(53 to 89 percent) below the sediment surface, followed by widgeon grass with

50 percent (Lewis and Phillips 1980).

Each seagrass species can occur as a monotypic seagrass bed or can be

found intermixed with the other species. In the Indian River Lagoon, some

seagrass beds consist of all seven species with the Halophila species scattered

throughout sparser areas within the bed.

Reproduction

Seagrasses reproduce sexually and asexually (or vegetatively). Vegetative

reproduction in seagrasses accounts for their capacity to produce high biomass

and extensive areal cover (Zieman and Zieman 1989). Information on sexual

reproduction in seagrasses is limited, though there is an abundance of

reproductive literature available on turtle grass. This species is sexually

dimorphic, producing separate male and female flowers. In South Florida,

turtle grass flowers develop in mid-May with fruits appearing 2 to 4 weeks

later (Zieman 1982). According to Grey and Moffler (1978), turtle grass may

also be dioecious, i.e., separate male and female plants.

Most of the available literature on sexual reproduction for the other species

is from studies conducted on the west coast of Florida. Phillips (1960) found

flowering widgeon grass in Tampa Bay. Lewis et al. (1985) collected flowering

manatee grass in the bay and found reproductive specimens of shoal grass in

nearby waters. Sexual reproduction in Johnsons seagrass is unknown; male

flowers have never been found. Hence, it is believed that Johnsons seagrass

disperses primarily through vegetative reproduction.

Wildlife Species of Concern

Federally listed animal species that depend upon or utilize the seagrass

community in South Florida include: American crocodile (Crocodylus acutus),

green sea turtle (Chelonia mydas), loggerhead sea turtle (Caretta caretta),

hawksbill sea turtle (Eretmochelys imbricata), leatherback sea turtle

(Dermochelys coriacea), Kemps ridley sea turtle (Lepidochelys kempii),

roseate tern (Sterna dougallii dougallii), wood stork (Mycteria americana),

bald eagle (Haliaeetus leucocephalus), and West Indian manatee (Trichechus

manatus). Biological accounts and recovery tasks for these species are

included in The Species section of this recovery plan. For a complete list of

State listed species that utilize seagrasses see Appendix C.

The coastal lagoons and estuaries are used as foraging habitat by several

species of birds including the osprey (Pandion haliaetus), magnificent

frigatebird (Fregata magnificens), least tern (Sterna antillarum), black
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SEAGRASSES Multi-Species Recovery Plan for South Florida

skimmer (Rynchops niger), American oystercatcher (Haematopus palliatus),

and eastern brown pelican (Pelecanus occidentalis). The State of Florida

classifies the osprey, American oystercatcher, eastern brown pelican, and black

skimmer as species of special concern, and the least tern as threatened.

The osprey is one of four subspecies distributed throughout the world, with

Pandion haliaetus carolinensis being the North American variant. In Florida,

the osprey is afforded the status of a State species of special concern for

Monroe County only. The osprey occurs throughout Florida wherever there are

sufficient bodies of open water for fishing. Nests are constructed on the tops of

cypress, mangrove, and pine trees (Ogden 1996), utility poles, radio towers,

channel markers (Schreiber and Schreiber 1977) and even in shrubs or on the

ground as in the Florida Bay area (Ogden 1977). In eastern North America, the

osprey is considered stable except for the declining Florida Bay population in

Everglades NP (Kushlan and Bass 1983; Poole 1989). Ospreys are considered

somewhat tolerant to human activity which makes them particularly vulnerable

to entanglement in fishing monofilament, striking power lines, hunting,

waterfront development, and human-induced changes in food availability

(Ogden 1996). This species is highly susceptible to environmental

contaminants, although there is no current threat from heavy metals, PCBs, and

pesticide contamination.

The Eastern brown pelican is a subspecies that occurs along the coastline

from Venezuela to Maryland and in the Caribbean. The brown pelican is a

marine species that nests and roosts on small islands (mostly < 5 ha) and

prefers areas vegetated by mangroves (Nesbitt 1996). Sand bars have also been

identified as an important loafing habitat (Schreiber and Schreiber 1982).

Kushlan and Frohring (1985) reported a 40 percent decrease in numbers of

pelicans in South Florida; however, since 1985, the overall status of the

population nesting in Florida is improving. Increasing development leading to

habitat degradation and decreased water quality are the most serious threats to

the eastern brown pelican. In the 1960s and 70s, this species was found to be

vulnerable to chemical contamination from pesticides and pollutants, such as

DDT, PCBs, and Endrin. Fishing line is another notable source of mortality.

Wading birds, such as the roseate spoonbill (Ajaia ajaja), reddish egret

(Egretta rufescens), great egret (Ardea alba), snowy egret (Egretta thula), little

blue heron (Egretta caerulea), and tricolored heron (Egretta tricolor)

frequently feed along the edges of shallow water seagrass beds. The State

classifies the roseate spoonbill, reddish egret, snowy egret, little blue heron,

and tricolored heron as species of special concern.

Fishes utilize the seagrass community for food and shelter. These include:

common snook (Centropomus undecimalus), spottail goby (Gobionellus

stigmaturus), mangrove rivulus (Rivulus marmoratus), and the key silverside

(Menidia conchorum). The State lists the common snook and the mangrove

rivulus as species of special concern, and the key silverside as threatened.

The spottail goby is a small fish (29 mm [1.14 in] standard length) known

from Bermuda, Florida, Cuba, Belize, and Panama (Pezold 1984) with Florida

populations ranging from Brevard to Monroe counties. The spottail goby has
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SEAGRASSES Multi-Species Recovery Plan for South Florida

been consistently collected in Fort Pierce Inlet in seagrass beds consisting of

manatee grass and shoal grass (Gilmore 1988). The spottail goby makes

burrows on nearby sand bars in very shallow water (depth < 0.5 m). Physical

disturbances and the degradation of water quality are major threats to the

spottail gobys seagrass habitat.

The key silverside, the smallest known species of Menidia (53 mm [2.08 in]

standard length), is limited to the Florida Keys from Long Key to Key West. The

key silverside swims in shallow, protected, coralline pools surrounded by

mangroves and often associated with turtle grass and macroalgae (Duggins et al.

1986). While this species is present at other locations within the Middle and

Lower Florida Keys (e.g., Long Key, Grassy Key, Big Pine Key, and Cudjoe

Key), it seems to have disappeared from Key West. The extent of urban

development is greater on Key West than the other islands; thus, the loss of

habitat (e.g., mangroves, seagrasses) can result in the extirpation of a small

localized population.

Plant Species of Concern

A federally listed plant species that depends upon or utilizes the seagrass

community includes the Johnsons seagrass. Although no biological account is

included in this recovery plan, a brief description is provided below. The

recovery plan for Johnsons seagrass is being developed by the U.S

Department of Commerces National Marine Fisheries Service.

The federally threatened Johnsons seagrass (Halophila johnsonii) is one of

twelve species of the genus Halophila. Johnsons seagrass is rare and exhibits

one of the most limited distributions of any seagrasses. Within its limited range

(lagoons on the east coast of Florida from Sebastian Inlet to central Biscayne

Bay), it is one of the least abundant species. Johnnsons seagrass limited

Eastern brown pelican.

Original photograph by Betty

Wargo.
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SEAGRASSES Multi-Species Recovery Plan for South Florida

reproductive capacity (apparently only asexual) and limited energy storage

capacity, makes it unlikely to repopulate an extirpated area. Identifying

characteristics of Halophila johnsonii include smooth foliage leaves in pairs 10

to 20 mm (0.39 to 0.79 inches) long, a creeping rhizome stem, sessile flowers,

and longnecked fruits.

Ecology

Seagrasses have been identified as an important habitat linked to the productivity

of our abundant fisheries (Ogden and Zieman 1977). This high productivity is

largely in response to the inherent ecological functions of seagrasses (Zieman

and Zieman 1989) which are: (1) seagrass growth is extremely rapid with the

leaves growing at about 5 mm (0.20 in) per day and over 10 mm (0.40 in) per

day under favorable circumstances; (2) the production of detritus and the

promotion of sedimentation provide organic matter for the plants and maintain

an active environment for nutrient recycling, i.e., seagrasses take up nutrients

from the sediments, transporting them through the plant and releasing them into

the water column through the leaves; (3) the pathways for photosynthetically

fixed energy is by direct grazing of living plant material, the utilization of detritus

from decaying plant matter, or the export of living and detrital plant material

from one location to another allowing for the distribution of energy away from

its original source; (4) seagrasses stabilize sediments with the roots and rhizomes

forming a complex, interlocking matrix, which binds the substrate and with the

leaves impeding current flow to reduce water velocity near the sediment-water

interface, which promotes settling of suspended particles as well as inhibits the

resuspension of organic and inorganic materials; (5) the surface of seagrass

leaves provide the substratum for attachments by a myriad of small algae and

animals (e.g., crustaceans, worms, sponges, bryozoans), which provide the basis

for food to a variety of larger seagrass-associated animals (Virnstein et al.1983);

and (6) seagrass beds serve as a place of both food and shelter for the juveniles

of a variety of shellfish and finfish of commercial and recreational importance.

In the subtropical waters of South Florida, seagrass beds often bridge large

areas between mangrove and coral reef communities. Many organisms that are

primarily associated with mangrove communities or coral reefs often feed in

adjacent seagrass meadows, which act as a transitional zone between these

ecological communities.

The spatial distribution of a given seagrass species is a function of

environmental conditions that include light, temperature, salinity, substrate,

waves and currents, and the availability of nutrients (Day et al. 1989).

Light

Estuarine seagrasses are most common in soft sediments of semi-sheltered areas

where depth and turbidity conditions allow sufficient light levels necessary for

growth and maintenance. Morris and Tomasko (1993) indicate that light is the

primary environmental factor controlling the survival and the depth distribution

of seagrasses. More specifically, light in the range of wavelengths from 400 to

700 nm (known as photosynthetically active radiation) provides the predominant

source of energy for seagrass photosynthesis to occur.
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SEAGRASSES Multi-Species Recovery Plan for South Florida

Turtle grass, manatee grass, and shoal grass require between 15 and 30

percent of the incident light (i.e., light at the waters surface) for long-term

survival; thus, they typically do not grow in water depths greater than 2 m (6.6

ft) for areas north of southern Biscayne Bay. The three species of Halophila

appear to need less incident light (approximately 6 to 12 percent) in order to

survive; hence, their occurrence in water as deep as 3 to 4 m (9.8 to 13.1 ft).

Factors that weaken or attenuate light as it travels through the water column are

phytoplankton blooms due to nutrient enrichment, turbidity, and water color

due to dissolved organic material. Additional factors that affect light

availability include shading either by epiphytes (small algae attached to the

surface of seagrass blades) or by structures (e.g., docks) located in shallow

water seagrass beds.

Another factor that limits the depth distribution of seagrasses is exposure

at the shallow end of the depth gradient (Kenworthy and Haunert 1991). Shoal

grass usually grows in the shallowest water and tolerates exposure better than

the other species. The next zone of seagrass is usually turtle grass, followed by

manatee grass with the Halophila group in deeper water. In some locations

(i.e., around inlets), Johnsons seagrass occurs both on sandbars exposed

during low tide as well as in 4-m (13.1-ft) deep tidal channels. Except for

southern Biscayne Bay, Florida Bay, and the Florida Keys, the average

maximum water depth for the vertical distribution of seagrasses in South

Florida is approximately 2 m (6.6 ft). In the relatively clear waters of these

areas, seagrasses can be found growing in water usually 6 to 7 m (19.7 to 22.9

ft) deep and even as deep as 10 m (32.8 ft).

As subtidal plants, seagrasses do not tolerate exposure well. When exposed

to the air, they lose water continuously until they dry out. Exposed leaves

usually die, then break off to be carried away with the current. Normally, the

rhizomes are not damaged and the plants continue to produce new leaves.

Temperature

Turtle grass, manatee grass, and shoal grass prefer temperatures between 20

and 30oC (68 and 86oF), although shoal grass is more eurythermal than the

other two species. Shoal grass, which is common in shallow water where

temperature variations tend to be greater, has a greater tolerance to lower

temperatures than either turtle grass or manatee grass. Seagrasses in deeper

water are buffered from cold temperatures because the overlying water has a

greater mass to be cooled.

Salinity

While each of the seagrasses can tolerate considerable short-term salinity

fluctuations, they all have an optimum salinity range from 24 to 35 parts per

thousand. As expected, shoal grass is broadly euryhaline, while manatee grass

is more stenohaline with turtle grass intermediate in its salinity tolerance. The

Halophila group is also more stenohaline, although Johnsons seagrass may be

tolerant of reduced salinities. Widgeon grass, again not a true seagrass, can

tolerate freshwater as well as hypersaline conditions.
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Although seagrasses may tolerate lowered salinities, the photosynthetic

rate in seagrasses is affected by changes in salinity. A decrease in salinity

carries a corresponding decrease in the photosynthetic rate of turtle grass.

Following the passage of a hurricane through South Florida in 1960, Thomas

et al. (1961) concluded that the damage to turtle grass by excessive fresh water

to have been more severe than the physical effects of the storm surge.

Sediments

Seagrasses grow in a wide variety of sediments from fine muds to coarse sandy

material. As rooted plants, seagrasses require a sufficient depth of sediment for

proper development. Sediments anchor the seagrass against the effects of water

surge and currents, and provide the matrix for growth and nutrient supply.

Sufficient sediment depth and physical stability is the single most important

sediment characteristic for seagrass growth and development. Requirements

for sediment depths vary with the different seagrass species. Shoal grass can

colonize thin sediments in an area of minimal hydraulic stability because of its

shallow, surficial root system. Although turtle grass can sparsely colonize thin

sediment layers over rock, this species requires at least 10 cm (3.94 in) of

sediment to achieve lush growth.

Seagrass blades can also affect the sediments they grow in. Dense seagrass

blades greatly affect the concentration of fine-grained particles in sediments

(Zieman 1982). For example, turtle grass blades can increase the percentage of

fine-grained particles in sediment two to five times. The primary physical

effects from seagrass blades are that they increase sedimentation rates,

concentrate fine-grained particles, and stabilize the deposition of sediments.

One of the ecological functions of a seagrass system is the ability to create a

relatively low-energy environment in an area of high energy and turbulence.

This is a key element in a plants efficiency to stabilize sediments.

Nutrients

The primary constituents of plant material are carbon, nitrogen, and

phosphorus. The accessibility of these components as dissolved nutrients is an

important factor governing the production of seagrass. In general, seagrasses

acquire most of their required inorganic carbon from free CO2 and assimilate

nitrogen and phosphorus from the sediments via their roots and rhizomes and

from the water column via their leaves.

Productivity

The major sources of primary production in South Floridas coastal ecosystems

are macrophytes, i.e., seagrasses, macroalgae, and mangroves. Algal communities

associated with seagrasses include benthic algae (attached to the substrate), drift

algae, and epiphytic algae. Seagrass leaves provide a relatively stable substrate for

epiphytic algae. The turnover of the epiphytic algal community is relatively rapid,

since the lifespan of a single leaf is quite limited. A typical turtle grass leaf has a

lifetime of 30 to 60 days (sometimes longer). The standing crop and productivity

of epiphytes and their contribution to the trophic food web of a system is highly

variable. In nutrient-poor waters, there are few epiphytes and, hence, very little

contribution. Conversely, in nutrient-enriched waters, like the Indian River
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Lagoon, epiphyte production is high. The relationship between these plants is that

of an ectoparasite, i.e., the relationship is beneficial to the epiphyte but detrimental

to the seagrass. Thus, in areas of high nutrient supply, epiphyte grazers are

extremely important in maintaining seagrass productivity.

Seagrasses themselves are very high in primary production and contribute

large quantities of detritus to an ecosystem (Zieman 1982). In Florida Bay and

the Keys, the standing crop of turtle grass beds may exceed 1,000 grams of dry

weight per meter squared. As such, the contribution of seagrass production to

this regions carbon budget may represent over 50 percent of the total

production within the estuary. Again, the factors that reduce seagrass

production are decreasing light levels, lack of nutrients, and increasing

epiphytic growth on the leaves.

Habitat

The structure of seagrass beds provides living space for a diverse assemblage of

mobile and sessile organisms (Harlin 1980, Stoner 1980). Biota present in

seagrasses are classified in a scheme that recognizes the central role of the

seagrass canopy (leaf blades) in organizing seagrass-associated communities. The

principal groups of such organisms are epiphytic (living on plants), epibenthic

(living on the sediment surface), infaunal (living within the sediments), and

nektonic (living in the water column). Representatives among these groups

include invertebrates (e.g., polychaetes, gastropods, bivalves, shrimps, lobsters,

crabs, urchins) and vertebrates (e.g., fishes, reptiles, birds, mammals).

Seagrass beds serve as nursery habitat where post-larval stages of

invertebrates and fishes develop to juvenile and adult phases (Virnstein et al.

1983, Lewis 1984). With their high productivity, extensive surface areas, and high

blade densities, seagrasses provide protection from predators, a substrate for the

attachment of sessile stages, and a plentiful food source. Notable examples of

organisms that benefit directly from their development within seagrass beds

include the pink shrimp (Penaeus duorarum), spiny lobster (Panulirus argus), and

several species of recreationally and commercially important fishes [e.g., spotted

sea trout (Cynoscion nebulosus), red drum (Sciaenops ocellata), snook

(Centropomus undecimalis), mangrove snapper (Lutjanus griseus)]. For example,

the pink shrimp harvest near the southwest coast of Florida was 4,535,970 kg (10

million pounds) per year prior to 1987. In the Indian River Lagoon, seagrasses

have been estimated to provide almost $30,000 per ha annually in economic

benefits based on fisheries alone (Virnstein and Morris 1996).

Seagrasses and associated epiphytes provide food for trophically higher

organisms by direct herbivory, as detrital food webs within seagrass beds, and

as detrital material exported out of a seagrass bed (Zieman 1982). Direct

herbivory is best exemplified by green sea turtles and the West Indian manatee

grazing in seagrasses. The detrital food web is another pathway of trophic

energy transfer. Typically, seagrass blades die and break off from the shoots to

form a layer of leaves on the sediment surface. This leaf litter is then subjected

to bacteria, fungi, and other microorganisms that contribute to the

decomposition of the plant material. The physical breakdown and reduction in

particle size of decaying seagrasses facilitates its assimilation by filter feeders
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(polychaetes) and deposit feeders (gastropods), which in turn, are fed upon by

omnivores (shrimps) and carnivores (fishes).

Status and Trends

With few exceptions, most of South Floridas coastal ecosystem has been

negatively affected either directly or indirectly from a number of man-made

activities: hydroperiod alterations, loss of upland vegetation, shoreline

modifications (e.g., removal of vegetation, installation of seawalls),

construction of causeways and bridges, dredging channels, increasing boat

traffic, point-source pollution (e.g., wastewater treatment facilities), nonpointsource pollution (e.g., stormwater runoff), and oil spills. The majority of these

direct and indirect effects are the result of Floridas rapidly expanding

population. Between 1970 and 1980, the States coastal counties increased in

population 44 percent, the greatest population increase in the nation during that

period. Between 1988 and 2010, South Florida will have four of the top 10

counties nationwide in absolute population change. Specifically, over 1.3

million additional persons are projected to move to Lee, Miami-Dade,

Broward, and Palm Beach counties by 2010. This growing population will

result in significant losses of habitat and living resources; increase demands on

water, energy, waste treatment and its disposal; and continue to diminish the

environmental quality of the region. For example, almost 207,000 vessels are

registered in Palm Beach, Broward, Miami-Dade, Monroe, Collier, and Lee

counties. Aside from the increasing number of registered vessels, the average

size and horsepower of these vessels are increasing as well, to the detriment of

shallow water seagrasses. As coastal populations increase throughout South

Florida, management of this growth to ameliorate the associated direct and

indirect effects becomes crucial.

Water Quality Degradation

Urban, industrial and agricultural development, and the construction of the

Central and Southern Florida Flood Control Project by the COE have had a

profound effect on the regions coastal habitats. The urban-developed ridge of

Miami-Dade, Broward, and Palm Beach counties has virtually eliminated the

natural community structure and function of over 161 km (100 mi) of the

southeast coast. Draining South Floridas interior wetlands into the adjacent

estuaries has resulted in increased turbidity as well as nutrient and pollutant

loadings (Indian River Lagoon NEP 1996).

While there is a lack of specific information on pesticide loads to South

Floridas estuaries, recent studies indicate that pesticides can enter the estuary with

stormwater runoff (Pait et al. 1992). High concentrations of trace metals (e.g.,

copper, cadmium, lead, and zinc) are found in specific locations, characteristically

near numerous and extensive boating facilities (e.g., marinas). Pathogenic bacteria

leaching from septic tanks into nearby estuaries, especially shellfish harvesting

areas, pose a public health problem. Nutrients from sewage disposal systems can

result in nutrification and eutrophication of nearshore areas.
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SEAGRASSES Multi-Species Recovery Plan for South Florida

Water management practices have resulted in the alteration of freshwater flow

into the estuaries. Such discharges introduce contaminants and pollutants into

these waterbodies. The frequency and timing of freshwater discharges have

influenced the loss of seagrasses in Florida Bay (Florida Bay Interagency Working

Group 1994). Episodic voluminous freshwater releases (due to excessive rainfall

events) through control structures in the Caloosahatchee and St. Lucie rivers have

a similar effect on the receiving estuaries, Charlotte Harbor and Indian River

Lagoon, respectively, because of the reduction in salinity for extended periods. In

addition, such freshwater releases/discharges carry pollutants, primarily nutrients

and sediments. During 1990 to 1992, the total nutrient loading related to

stormwater runoff into the Indian River Lagoon was estimated to be over 3 million

pounds per year.

Habitat Loss

From the 1920s to the 1960s, Floridas coastal zone underwent tremendous

alterations as a result of the lack of proper management of its explosive

population increase. During this period, coastal communities arose from the

mangrove marshes that dominated South Floridas estuarine landscape. Many

of these communities were built by dredging and filling emergent and

submerged wetlands for residential development. Associated with such

communities were numerous man-made canals and waterways constructed to

facilitate the demand for waterfront property. Channels were dredged

through seagrasses to provide navigational access to and from waterfront

properties. Throughout Florida, approximately 7,500 ha (18,532 acres) of

submerged land have been filled by dredged material to facilitate residential

and commercial development (Zieman 1982). Aside from the direct effect of

burial, resuspended particles from spoil deposition reduce light levels thereby

restricting primary productivity. Such rampant dredge and fill activities

resulted in the destruction of seagrass beds throughout South Florida.

Another threat to seagrass communities has been, and continues to be, the

increasing number of boats on Floridas coastal waterways. Used for recreation

and/or work, many of these vessels operate in water shallower than their drafts,

resulting in propeller scarring of seagrasses. Of the States 1.1 million ha

(2,718,100 acres) of seagrass, more than 70,000 ha (172,970 acres) have been

lightly, moderately, or severely scarred by boat propellers (Sargent et al. 1995).

As the population began to increase in these newly erected coastal

communities, nutrients from sewage discharged into South Floridas estuaries

also increased. Nutrient enrichment in these embayments stimulated the

production of epiphytes and phytoplankton which in turn inhibited the growth

and survival of seagrasses. Hence, the loss of habitat due to physical

disturbance and the degradation of water quality resulted in a decline in

fisheries resources throughout South Floridas coastal ecosystem.

Aside from habitat degradation, fisheries resources have been dramatically

affected by overfishing. With the decline in seagrasses, nursery and rearing

habitat were significantly reduced. Furthermore, with an increase in

population, there was a concurrent increase in pressure on the existing fish

stocks. In Sarasota Bay, spotted seatrout landings were down 50 percent,
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SEAGRASSES Multi-Species Recovery Plan for South Florida

although seven times more recreational anglers were using the bay than in the

1950s (Sarasota Bay NEP 1995).

From 1950 to 1985, seagrass coverage declined approximately 35 percent in

the Indian River Lagoon (Haddad and Harris 1985). Since the 1950s, seagrasses

have declined almost 30 percent in Sarasota Bay (Sarasota Bay NEP 1995). Other

estuaries that have experienced similar deceases in seagrass abundance and

distribution include Lake Worth Lagoon, Biscayne Bay, Estero Bay, and Charlotte

Harbor.

Recent seagrass assessments conducted in 1995 indicate that the overall

change in seagrass coverage in the Indian River Lagoon from 1943 to 1992 has

been a 20 percent decrease (R.W. Virnstein, SJRWMD, personal communication

1998). While seagrasses declined or disappeared in some sections of the lagoon,

they increased in coverage in those areas where inlets have been stabilized and

increased in size. Five of the six inlets along the lagoon are man-made; hence,

their presence allowed the introduction of clear oceanic water into the lagoon,

which influenced the growth of seagrasses near these estuarine connections.

Florida Bay

For Florida Bay, the decline in seagrasses was not the result of dredge and fill

activities. Since most of the bay (220,200 ha [544,114 acres]) is within the

boundaries of Everglades NP, it is protected from large-scale human-induced

direct physical disturbances. Historically, seagrasses have been the dominant

primary producers in Florida Bay. However, since 1987, massive seagrass

mortality has occurred in the bay with over 18 percent of the total bay area

affected (> 40,000 ha [98,840 acres]). The rate of seagrass die-off

accelerated in 1992. Such massive habitat loss has substantially affected fish

and wildlife resources. As a result of the seagrass die-off, the pink shrimp

harvest decreased from 10 million pounds in 1986 to four million pounds in

1987, a decline of 60 percent.

The most likely cause for seagrass die-off appears to be physiological

stress from high salinities and high temperatures in the 1980s coupled with the

long-term anthropogenic reduction of freshwater inflow to Florida Bay

(Florida Bay Interagency Working Group 1994). Additional stressors include

sulfide toxicity as a result of photosynthesis/respiration imbalance and a

disease which was also probably stress induced. An additional postulated cause

of the Bays seagrass mass mortality is nutrient enrichment from the mainland

and the Keys.

Boating Impacts

Currently, the most common form of physical destruction to seagrasses is the

dredging of plant material (blades as well as roots and rhizomes) by boat

propellers and vessel groundings on shallow seagrass beds. This form of

seagrass destruction, known as prop scarring, occurs in shallow water areas

throughout South Florida. In leading the State in total seagrass coverage,

Monroe County also leads in scarred seagrass beds with almost 12,200 ha

(30,146 acres). Zieman (1976) estimated that it takes several years for turtle

grasses to begin recovery from prop scarring. Sargent et al. (1995) indicate
Page 3-611

SEAGRASSES Multi-Species Recovery Plan for South Florida

that a prop scar within a turtle grass bed averages 3 to 5 years to begin healing.

However, a recent study indicates that moderate scarring (i.e., minimal vertical

relief in the scar) takes 12 to 15 years to begin recovery (J.W. Kenworthy,

NMFS, personal communication 1998). Deeper scars require decades to

recover. In Tampa Bay, Lewis and Estevez (1988) indicate complete seagrassscar recovery may take as long as 10 years. This period is probably much

longer in areas of poor water quality and where scarring is severe and

repetitive; some scarred beds may never recover.

Another serious form of physical disturbance to seagrasses is from boat

wakes. Based on data indicating decreased light penetration associated with

weekend boat traffic, Kenworthy et al. (1988) found a possible cause-effect

relationship between boating activities and increased turbidity. Seagrasses are

sensitive to decreased light penetration. Increased boating activity and larger

boats have resulted in chronic conditions of resuspended sediments and eroded

seagrass beds along the edges of deeper channels, especially in the Upper and

Middle Florida Keys (C. Kruer, Florida Keys Environmental Restoration Trust

Fund, personal communication 1998).

Once seagrasses are lost within an embayment, that systems capacity to

stabilize sediments is also lost. A negative cycle is initiated when resuspended

sediments reduce the amount of light available for seagrasses to survive and

grow, which reduces seagrass coverage, which reduces sediment stabilization,

resulting in additional resuspended sediments.

Management

Much of Floridas distinctive character lies in the beauty of its natural features,

especially its coastal areas. This natural beauty has always been one of

Floridas major attractions for both residents and tourists. Ironically, the very

features that have attracted people to Florida have been physically altered by

the increased population pressure.

It was during the early 1960s that the public became aware of the

importance of Floridas coastal environment. During this period, dredge and

fill activities were regulated for the first time by the State of Florida. In 1972,

the COE authorized dredge and fill activities nationwide in accordance with

section 404 of the Clean Water Act. With the passage of the Warren Henderson

Wetlands Protection Act of 1984, wetland regulations and permitting were

standardized throughout Florida. Once these regulatory measures were

implemented, the rate of habitat loss due to physical alterations began to

decline.

Not all of the seagrass habitat in South Florida is in peril. Hobe Sound,

southern Biscayne Bay, Card Sound, and some areas in the Florida Keys

exhibit very healthy seagrass beds. It is those seagrass beds adjacent to

urbanized coastal communities that have been ecologically stressed and

physically damaged for several years. During the past two decades, several

management programs designed to improve water quality and protect

biological resources in coastal regions were implemented by the Federal

government and the State of Florida. A summary of these management

programs and a table listing them follows:
Page 3-612

SEAGRASSES Multi-Species Recovery Plan for South Florida

Aquatic Preserves

To protect the States distinctive and unique coastal features for the enjoyment of

future generations, the Florida Legislature created a series of aquatic preserves

around the State in the late 1960s. Aquatic preserves are submerged lands of

exceptional beauty that are to be maintained in their natural or existing

conditions. In 1975, the Florida Aquatic Preserve Act was passed establishing a

standardized set of management criteria for all aquatic preserves, both existing

and future. Administered by the DEP, this set of management criteria was

developed to eliminate or minimize the effects of specific activities on coastal

resources such as seagrasses and mangroves. For example, dredging and/or

constructing multi-slip docking facilities in seagrass beds is prohibited. There are

several aquatic preserve programs around South Florida (Table 1).

Coastal Zone Management Program

Authorized by the Coastal Zone Management Act of 1972, the Coastal Zone

Management (CZM) Program is a voluntary partnership between the Federal

government and U.S. coastal states and territories. Through its partnerships, the

CZM program serves to preserve, protect, develop, restore, and enhance the

resources of the nations coastal zone; to encourage and assist the states in

exercising their responsibilities in the wise use of land and water resources of the

coastal zone; and to encourage the preparation of special area management plans

designed to protect significant natural resources, influence reasonable coastaldependent economic growth, improve protection of life and property in

hazardous areas, and improve predictability in governmental decision-making. In

essence, the CZM program uses a comprehensive resource management

approach by balancing land and water uses while protecting sensitive resources.

National Estuarine Research Reserves

On a national scale, the value of estuaries is tremendously important. These tidally

influenced ecological systems provide habitat for millions of birds, mammals,

fish, and other wildlife; function as a nursery ground for many marine organisms,

including commercially valuable fish species; produce tremendous amounts of

organic matter; filter water draining off uplands by removing sediments and

nutrients; and function as a natural buffer between the land and the ocean by

dissipating storm surges, thereby protecting private property. Recognizing the

value of estuaries and the effect human activities would have on them, Congress

created the National Estuarine Research Reserve System (NERRS) along with the

passage of the Coastal Zone Management Act in 1972. Administered by the

National Oceanic and Atmospheric Administration (NOAA), NERRS is dedicated

to fostering a system of estuary reserves that represent the wide range of coastal

and estuarine habitats found in the United States and its territories. In pursuing this

goal, NERRS works with Federal and State authorities to establish, manage and

maintain reserves, and to provide for their long-term stewardship. Research and

education are the principal program components toward meeting this goal.

National Marine Sanctuaries
Page 3-613

SEAGRASSES Multi-Species Recovery Plan for South Florida

In creating the National Marine Sanctuary Program through the passage of the

Marine Protection, Research, and Sanctuaries Act of 1972, Congress was

extending the nations protective interests beyond the estuaries and into the

marine environment. Administered by NOAA, the mission of the National

Marine Sanctuary Program is to identify, designate, and manage areas of the

marine environment with significant ecological, conservation, research,

educational, recreational, historical, and aesthetic qualities. The programs

goals are to provide enhanced resource protection through conservation and

management of the sanctuary; to support, promote, and coordinate scientific

research on marine resources of the sanctuary; and to enhance public

awareness and wise use of the marine environment.

National Estuary Programs

Congress continued its efforts toward protecting the nations estuaries by

establishing the National Estuary Program (NEP) under the Water Quality Act

of 1987. Administered by the EPA, the NEP identified nationally significant

estuaries threatened by pollution and development. The programs goals are to

protect and improve water quality and to enhance living coastal resources

through the preparation of a comprehensive conservation management plan

(CCMP). Implementation of the CCMP ensures the ecological integrity of that

particular estuary.

Surface Water Improvement and Management (SWIM) Programs

Floridas rapidly expanding population increased the number of point and

nonpoint sources of pollution and resulted in the destruction of ecological

communities. Consequently, many of Floridas natural surface water systems

(e.g., lakes, springs, rivers, bays, and estuaries) were becoming degraded,

making them unable to support plant and animal life, unfit for recreation, and

potentially hazardous to human health. In 1987, the Florida Legislature enacted

the Surface Water Improvement and Management (SWIM) Act, which directed

the States five water management districts, with the cooperation of State

agencies and local governments, to develop and implement plans to clean up

and protect specific waterbodies. Hence, affected waterbodies were prioritized

with a common SWIM goal established for each. Essentially, each system shall

be improved and managed at a level of quality that provides aesthetic and

recreational pleasure for the people of the State; that provides habitat for native

plants, fish, and wildlife, including threatened and endangered species; and that

attracts visitors and accrues other economic benefits. Since SWIM, many

coastal communities have implemented surface water management programs

which have improved the quality of the water discharging into adjacent

estuaries, thereby improving water quality within the waterbody itself. The

three water management districts responsible for administering the following

SWIM programs in South Florida are: St. Johns River Water Management

District, South Florida Water Management District, and Southwest Florida

Water Management District.

Florida Bay Program Management Committee
Page 3-614

SEAGRASSES Multi-Species Recovery Plan for South Florida

The Interagency Task Force, a multi-agency group established to implement

the South Florida Ecosystem Restoration Initiative, created the South Florida

Management and Coordination Working Group. The Working Group then

created the Florida Bay Program Management Committee (PMC), an eightmember interagency committee, whose purpose was to integrate the science

plan of Florida Bay into a regional ecosystem-based science program. Since

1994, the PMC has focused its efforts on integrating the data and developing

the models essential for understanding the bay as an ecosystem that is strongly

influenced by human forces. By collaborating with the member agencies on a

research strategy for Florida Bay, the PMCs goal is to provide the scientific

information critical to the restoration of the Bay, e.g., the eventual

recolonization of seagrasses throughout the Bay.

Another statewide management initiative is a program with the potential to

reduce prop scarring and physical destruction of seagrasses by vessels. To be

implemented by local governments, the program components include boater

education, installing aids to navigation, increased enforcement, and

designating limited-motoring zones. Monroe County is preparing to implement

the Channel Marking Master Plan for the Florida Keys, which was completed

in January 1998. Despite these measures, the scarring of seagrasses continues

in the Keys largely due to an increase in the number of boats and in the number

of boaters operating in shallow water seagrass beds.

Federal and State land management programs can extend protection over

seagrasses when these submerged resources are within their boundaries. Such

programs in South Florida include the Pelican Island NWR, Hobe Sound

NWR, Biscayne Bay NP, Everglades NP, Crocodile Lakes NWR, John

Pennekamp Coral Reef SP, National Key Deer Refuge, Great White Heron

NWR, Key West NWR, Dry Tortugas NP, and J.N. Ding Darling NWR.

Currently, many of these management programs are having a beneficial

effect on South Floridas estuaries. In some coastal embayments, seagrass

coverage is increasing largely due to improved water quality conditions. Since

April 1996, treated wastewater is no longer directly discharged into the Indian

River Lagoon. The installation of baffle boxes designed to filter stormwater

runoff has also improved water quality in the Lagoon. Seagrasses have

recovered in parts of Biscayne Bay due to a reduction in turbidity. Boating

traffic was eroding the shorelines of spoil islands located in the Bay. Once these

shorelines were stabilized, turbidity decreased and water clarity increased. Even

the seagrass community in Florida Bay has experienced some degree of

recovery. While turtle grass is continuing to decline in western Florida Bay,

shoal grass is revegetating some parts of eastern Florida Bay. Treating

stormwater runoff has improved water quality conditions in Sarasota Bay by

reducing nitrogen and contaminant loadings. Though not within the boundaries

of the South Florida Ecosystem, Tampa Bay has experienced increased seagrass

coverages, again, as the result of improved water quality conditions.
Page 3-615

SEAGRASSES Multi-Species Recovery Plan for South Florida

PROGRAM NAME DESIGNATED STATUS OF

MANAGEMENT PLAN

Indian River Lagoon - Malabar to Vero Beach

- Vero Beach to Fort Pierce

- Jensen Beach to Jupiter Inlet

North Fork St. Lucie River

Loxahatchee River - Lake Worth Creek

Biscayne Bay - Cape Florida

Biscayne Bay - Card Sound

Lignumvitae Key

Coupon Bight

Cape Romano - Ten Thousand Islands

Rookery Bay

Estero Bay

Pine Island Sound

Matlacha Pass

Cape Haze

Gasparilla Sound - Charlotte Harbor

Lemon Bay

Indian River Lagoon - St. Lucie River

Indian River Lagoon - Loxahatchee River

Biscayne Bay

Caloosahatchee

Charlotte Harbor

Rookery Bay

Florida Keys

Sarasota Bay

Indian River Lagoon

Charlotte Harbor

Surface Water Improvement and Management (SWIM) Programs

Aquatic Preserves

National Estuarine Research Reserves

National Marine Sanctuaries

National Estuary Programs

1970

1970

1973

1972

1970

1970

1974

1972

1972

1970

1975

1975

1970

1972

1975

1979

1986

1987

1988

1987

1987

1988

1978

1990

1988

1990

1995

completed 1986

completed 1985

completed 1985, revised 1990

completed 1984

completed 1984

no plan

no plan

completed 1991

completed 1992

completed 1988

completed 1988

completed 1983

completed 1983

completed 1983

completed 1983

completed 1983

completed 1992

completed 1989, revised 1994

completed 1989, revised 1994

completed 1988, revised 1995

no plan

completed 1988, revised 1993

completed 1995

completed 1996

CCMP implemented 1995

CCMP implemented 1995

developing CCMP

Table 1. State and Federal management programs that affect South Florida's estuaries

listed by program name, date established/designated, and the status of its associated management plan.
Page 3-616

SEAGRASSES Multi-Species Recovery Plan for South Florida

Burrell, D.C., and J.R. Schubel. 1977. Seagrass ecosystem oceanography. Pages 195-

227 in C.P. McRoy and C. Helfferich (eds.), Seagrass ecosystems. Marcel Dekker,

New York, New York.

Day Jr., J.W., C.A.S. Hall, W.M. Kemp, and A. Yanez-Arancibia. 1989. Estuarine

ecology. John Wiley & Sons, Inc., New York, New York.

Duggins, C.F., Jr., A.A. Karlin, K. Relyea, and R.W. Yerger. 1986. Systematics of the

key silverside, Menidia conchorum with comments on other Menidia species

(Pisces: Atherinidae). Tulane Studies in Zoology and Botany 25(2):133-150.

Florida Bay Science Plan [Florida Bay Interagency Working Group]. 1994. Planning

document provided to the Interagency Working Group on Florida Bay.

Gilmore, R.G. 1988. Subtropical seagrass fish communities: population dynamics,

species guilds, and microhabitat associations in the Indian River Lagoon, Florida.

Ph.D. dissertation (unpublished), Florida Institute of Technology, Melbourne,

Florida.

Grey, W.F., and M.D. Moffler. 1978. Flowering of the seagrass Thalassia testudinum

(Hydrocharitaceae) in Tampa Bay, Florida. Aquatic Botany 2:93-101.

Haddad, K.D., and B.A. Harris. 1985. Assessment and trends of Floridas marine

fisheries habitat: an integration of aerial photography and thematic mapper

imagery. Pages 130-138 in Anonymous (eds.), Proceedings of machine processing

of remotely sensed data with special emphasis on quantifying global process:

models, sensor systems, and analytical methods. Laboratory Applications in

Remote Sensing. Purdue University, West Lafayette, Indiana.

Harlin, M.M. 1980. Seagrass epiphytes. Pages 117-151 in R.C. Phillips and C.P.

McRoy (eds.), Handbook of seagrass biology: an ecosystem perspective. Garland

STPM Press, New York, New York.

Indian River Lagoon comprehensive conservation and management plan. 1996. Final

Draft. Indian River Lagoon National Estuary Program, Melbourne, Florida.

Kenworthy, J.W. 1997. An updated biological status review and summary of the

proceedings of a workshop to review the biological status of the seagrass,

Halophila johnsonii Eiseman. Final report submitted to Office of Protected

Species, National Marine Fisheries Service, National Oceanic and Atmospheric

Administration, Silver Spring, Maryland.

Kenworthy, J.W. 1998. Phone conversation. May 20, 1998.

Kenworthy, J.W., and D.E. Haunert. 1991. The light requirements of seagrasses:

proceedings of a workshop to examine the capability of water quality criteria,

standards and monitoring programs to protect seagrasses from deteriorating water

transparency. National Oceanic and Atmospheric Administration Technical

memorandum NMFS-SEFC-287.

Kenworthy, J.W., M.S. Fonseca, D.E. McIvor, and G.W. Thayer. 1988. The submarine

light regime and ecological status of seagrasses in Hobe Sound, Florida. Annual

Report. Beaufort Laboratory, National Marine Fisheries Service, National Oceanic

and Atmospheric Administration, Beaufort, North Carolina.

Kruer, C.R. 1998. Phone conversation. May 20, 1998.

Literature Cited
Page 3-617

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Kushlan, J.A., and O.L. Bass, Jr. 1983. Decreases in the southern Florida osprey

population, a possible result of food stress. Pages 187-200 in D.M. Bird (ed.),

Biology and management of bald eagles and ospreys. MacDonald Raptor

Research Center, McGill University, Harpell Press, St. Anne de Bellevue, Quebec.

Kushlan, J.A., and P.C. Frohring. 1985. Decreases in the brown pelican population in

southern Florida. Colonial Waterbirds 8:83-95.

Lewis, L.J. 1984. Distribution of macrobenthic crustaceans associated with Thalassia,

Halodule, and bare sand substrata. Marine Ecology progress series 19:101-113.

Lewis, R.R., and E.D. Estevez. 1988. The ecology of Tampa Bay: an estuarine profile.

U.S. Fish and Wildlife Service, biological report 85 (7.18). Washington, D.C.

Lewis, R.R., and R.C. Phillips. 1980. Seagrass mapping project. Hillsborough County,

Florida. Tampa Port Authority.

Lewis, R.R., M.J. Durako, M.D. Moffler, and R.C. Phillips. 1985. Seagrass meadows

of Tampa Bay - a review. Pages 216-246 in S.F. Treat, J.L. Simon, R.R. Lewis, and

R.L. Whitman (eds.), Proceedings in Tampa Bay area scientific information

symposium. Florida Sea Grant report 65. Burgess Publication Co., Minneapolis,

Minnesota.

Livingston, R.J. 1990. Inshore marine habitats. Pages 561-573 in R.L. Myers and J.J.

Ewel (eds.), Ecosystems of Florida. University of Central Florida Press, Orlando,

Florida.

Morris, L.J., and D.A. Tomasko (eds.). 1993. Proceedings and conclusions of

workshops on submerged aquatic vegetation and photosynthetically active

radiation. Special publication SJ93-SP13. St. Johns River Water Management

District, Palatka, Florida.

Nesbitt, S.A. 1996. Eastern brown pelican. Pages 144-155 in Rodgers, J.A. Jr., H.W.

Kale II, and H.T. Smith (eds.), Rare and endangered biota of Florida. Volume V.

Birds. University Press of Florida, Gainesville, Florida.

Ogden, J.C. 1977. Preliminary report on a study of Florida Bay ospreys. Pages 143-151 in

J.C. Ogden (ed.), Transactions of the North American osprey research conference.

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Ogden, J.C. 1996. Osprey. Pages 170-178 in Rodgers, J.A. Jr., H.W. Kale II, and H. T.

Smith (eds.), Rare and endangered biota of Florida. Volume V. Birds. University

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Ogden, J.C., and J.C. Zieman. 1977. Ecological aspects of coral reef-seagrass bed

contracts in the Caribbean. Proceedings of the 3rd international symposium on

coral reefs. University of Miami 3:377-382.

Pait, A.S., A.E. DeSouza, and D.R.G. Sarrow. 1992. Agricultural pesticide use in

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dissertation (unpublished), University of Texas, Austin, Texas.

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Poole, A.F. 1989. Ospreys. A natural and unnatural history. Cambridge University

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Sargent, F.J., T.J. Leary, D.W. Crewz, and C.R. Kruer. 1995. Scarring of Floridas

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Schreiber, R.W., and E.A. Schreiber. 1977. Observations of ospreys nesting on

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Schreiber, R.W., and E.A. Schreiber. 1982. Essential habitat of the brown pelican in

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Virnstein, R.W., and L.J. Morris. 1996. Seagrass preservation and restoration: a

diagnostic plan for the Indian River Lagoon. Technical memorandum no. 14. St.

Johns River Water Management District, Palatka, Florida.

Virnstein, R.W., P.S. Mikkelsen, K.D. Cairns, and M.A. Capone. 1983. Seagrass beds

versus sand bottoms: the trophic importance of their associated benthic

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Zieman, J.C. 1976. The ecological effects of physical damage from motor boats on

turtle grass beds in southern Florida. Aquatic Botany 2:127-139.

Zieman, J.C. 1982. The ecology of the seagrasses of south Florida: a community

profile. U.S. Fish and Wildlife Service, Office of Biological Services, Washington,

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Zieman, J.C., and R.T. Zieman. 1989. The ecology of the seagrass meadows of the west

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Page 3-619

Restoration of

Seagrasses

Community-level Restoration Actions

1. Identify the extent of seagrass habitat. Using existing GIS databases, satellite/thematic images

and aerial photographs (scales =1:12,000; 1:24,000; or 1:48,000) coupled with ground-truthing

efforts, produce maps of seagrass distribution and abundance as an initial step in evaluating the

extent of seagrasses in South Florida. Many of the regions estuaries have already been mapped

or are currently being mapped for seagrasses (e.g., Indian River Lagoon, Biscayne Bay, Florida

Bay, and the Florida Keys).

1.1. Conduct an inventory of seagrass habitat using available satellite/thematic

imagery, aerial photographs, and ground-truthing efforts once every 3 years.

Water clarity conditions for aerial photography are best during winter to spring;

Restoration Objective:

Restoration Criteria:

Restoration Objective: Maintain and increase seagrass habitat in South Florida.

Restoration Criteria

South Florida can contribute to the protection, enhancement, and restoration of seagrass ecosystems in

Florida by maintaining or improving water quality conditions necessary for seagrass growth within the

regions estuaries. The protection, enhancement, and restoration of seagrass habitat in South Florida will

contribute to the recovery of listed plant and animal species as well as maintain the ecological functions

associated with this community, such as high primary and secondary production; enhancing water quality by

stabilizing sediments and removing nutrients; and providing shelter, foraging, and nursery habitat for

numerous invertebrates and vertebrates important to recreational and commercial fisheries. The preservation

of this community will enhance the overall natural setting and visual aesthetics of Floridas coastal

landscape and contribute significantly to the economy of South Florida and to the State of Florida.

The restoration objective for seagrass habitat in South Florida will be achieved when: (1) the spatial

extent of seagrasses has been identified; (2) the condition of existing seagrasses has been assessed by

monitoring specific locations; (3) the relationship between light and water quality to seagrasses has been

determined from these monitoring sites; (4) predictive models have been developed that link light

attenuation and nutrient loadings to water quality and to epiphyte abundance; (5) the models set pollution

load reduction goals to improve or maintain water quality conditions necessary for seagrass survival and

growth; (6) management actions have been implemented that result in protecting, enhancing, and restoring

seagrasses; and (7) additional protective measures have been implemented to prevent further physical

disturbance of seagrass habitat. Increased seagrass distribution and abundance will be used as measures of

success to inform the public in recognizing the importance of this community to fisheries resources, wading

birds, and listed species such as the Florida manatee.
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however, seagrass abundance is greatest in the summer. Ground-truthing verifies the

interpretation of the large-scale aerial photographs.

1.2. Maintain the seagrass data obtained/collected from the inventory in a GIS

database. Digitize the data into a GIS database (e.g., ARC/INFO) from which maps

can be produced.

1.3. Create a regionwide classification scheme of seagrass habitat. Classifying

seagrasses as either dense continuous beds (seagrass beds with some sand patches;

coverage > 50%) or patchy beds (sand areas with some patches of seagrass; coverage

< 50%) improves the repeatability of determining seagrass coverage and is necessary

to consistently map seagrass habitat.

1.4. Map the distribution and abundance of seagrasses throughout the region.

Mapping the abundance of seagrasses can identify both problem and healthy

areas. Problem areas can be investigated to identify the cause of the problem.

Healthy areas can be designated for protection. Mapping can plot changes in the

amount and density of seagrass coverage, thereby providing a trend analysis of this

community type.

2. Assess the status and condition of existing seagrass habitat. Monitoring selected areas

within the region will be used to determine if seagrass beds are healthy or stressed and whether

conditions are stable, improving, or declining and to what degree.

2.1. Use low-level aerial photography to map the distribution and abundance of

seagrasses in a selected area. Low-level aerial photography can record conditions

and document changes in seagrass beds (0.1 to 10 m2 [1.07 to 107.6 ft2] in size) at

selected sites on a small scale (0.1 to 10,000 ha [0.3 to 24,710 acres]).

2.2. Establish fixed transects to detect changes in depth distribution, abundance, and

species composition of seagrasses. Sampling fixed transects can reliably detect finescale changes in depth distribution, abundance, and species composition over time.

3. Determine the relationship between light and water quality to seagrasses. Increases in

turbidity and nutrients occur both in short pulses and over long periods of time. In order to

determine the effects to South Floridas estuaries from episodic events, measurements (i.e.,

monitoring) of photosynthetically active radiation, water quality, and seagrass cover and

abundance need to be taken at the fixed transect sites. Implement site-specific monitoring

protocols to identify causes of seagrass decline. Integrating these measurements should

identify the effects light and water quality have on seagrasses.

3.1. Implement sampling protocols to measure photosynthetically active radiation.

The sampling methodology includes, but is not limited to, using quantum sensors to

measure light at the waters surface and underwater.

3.2. Implement monitoring protocols to sample water quality parameters. These

parameters include, but are not limited to, temperature, salinity, dissolved oxygen,

nitrogen, phosphorus, suspended solids, chlorophyll, turbidity, and color.

3.3. Implement sampling protocols to measure seagrass parameters. These

parameters include, but are not limited to, percent cover, biomass, shoot density,

canopy height, species composition, productivity, and abundance of drift and

epiphytic algae.
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4. Develop predictive models that link light attenuation to water quality and to nutrient

loadings and epiphyte abundance. The most critical factor affecting seagrass distribution

and abundance is light availability, which is a function of water quality. Hence, identifying the

water quality constituents regulating light availability in the water column is an initial step.

Understanding how nutrients and epiphytes affect light availability is just as crucial. These

predictive models will be linked to identify pollutant load reduction goals for specific

estuaries or specific segments within estuaries.

4.1. Develop a model that relates light attenuation in the water column to various

water quality constituents. Light attenuation will be modeled based on various

water quality constituents influenced by hydrodynamic (circulation) forces.

Predicted effects on light in the water column, linked with the findings from the sitespecific monitoring, will then provide a predictor of stress imposed on seagrass

systems.

4.2. Develop a model that relates nutrients to abundance of epiphytes and quantifies

the resultant light attenuation. Epiphytes can reduce light reaching the seagrass

blade by 50 to 80 percent. Two factors known to influence epiphyte abundance are

dissolved nutrients in the water column and grazers (e.g., snails, small crustaceans)

on the blades surface. If grazers are absent, epiphytes can grow unchecked. The

epiphyte light attenuation model will address the balance between nutrient effects

and grazing effects.

5. Implement management actions that will improve or maintain water quality conditions

necessary for seagrass growth. Improving the management of potential sources for

degradation will provide better water quality, which produces healthy seagrasses and

maintains biological productivity.

5.1. Based on seagrass light requirements, establish pollutant load reduction goals

for a specific waterbody or even a segment within a waterbody. Setting the

pollutant load reduction goals for a particular waterbody should result in reduced

loadings as predicted by the models. The management actions required to reach the

pollutant load reducton goals can include stormwater treatment, wastewater reuse,

and best management practices for upland use (e.g., landscaping options such as a

reduction in fertilizers).

5.2. Monitor these waterbodies or segments within them for the predicted responses

to the implementation of management actions. Continue surveying the fixed

transects to detect changes in seagrass distribution, abundance, and species

composition.

6. Restore seagrass habitat, where feasible. Restoration of lost seagrass beds requires adequate

mapping of sites known to have been vegetated with seagrasses in the past; reducing excessive

nutrients and suspended particulates to allow seagrass beds to recover naturally; and possibly

replanting candidate sites.

6.1. Identify areas wherein stressed or lost seagrass beds are in need of restoration.

Once the pollutant load reduction goals have been set and the management actions

implemented, seagrasses should recruit naturally into the site. However, certain

conditions may require a site to be replanted with donor specimens from another

location.
6.2. Rehabilitate seagrass communities where they have been destroyed by human

activities (e.g., prop scars) by replanting.

7. Preserve existing seagrass habitat. Most of South Floridas seagrass beds vegetate

submerged land that is in sovereign ownership by the State. Much of this submerged land is

under additional protection by the establishment of national parks, national wildlife refuges, a

national marine sanctuary as well as the designation of a national estuarine research reserve

and several aquatic preserves. Seagrass communities outside of these protective boundaries,

especially those parcels in private ownership, require even greater attention. Such areas are

often at risk from human activities simply because they do not have the unique resource

designations that other areas have within South Florida.

7.1. Use existing regulatory authorities to protect seagrass habitat. Seagrasses are

currently protected by law from human activities on State-owned submerged lands

within designated aquatic preserves and within the boundaries of federallydesignated areas, such as the Florida Keys National Marine Sanctuary, Biscayne NP,

Everglades NP, and Rookery Bay National Estuarine Research Reserve. In those

instances where seagrasses are damaged within these boundaries, enforcement of

existing regulations is necessary.

7.2. Prevent the additional degradation of existing seagrass habitat. Implement a

multiple approach management program to reduce prop scarring of shallow water

seagrass beds. The management program should include increased boater education,

installing channel markers, active enforcement, and establishing limited motoring

zones. Over the long term, this comprehensive approach should reduce scarring to

levels that do not significantly affect habitat quality and quantity.

7.3. Identify and acquire privately-owned submerged land vegetated with

seagrasses. Public acquisition of these few tracts will preserve the seagrass habitat

associated with them.

8. Promote research. Because of the problems experienced by Florida Bay, the effect of

extensive phytoplankton blooms (i.e., light availability, nutrient regimes) as well as slime

mold disease (i.e., Labyrinthula) on seagrass communities should continue to be investigated.

In addition, the effects of freshwater flows (i.e., quality, quantity, timing, distribution) on

seagrasses should be investigated further.

9. Increase public awareness. Present literature, maps, and slide presentations on the

importance of seagrass habitat in South Floridas coastal landscape. Emphasize the

significance of the ecological functions and economic value associated with this community.

Accomplishing this task will enlist support from the public at large to continue the protection,

enhancement, and restoration efforts of seagrass habitat.

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