TECHNICAL REPORTS

FMRI Technical Report TR-1 1995

Florida Department of

Environmental Protection

Scarring of Florida’s Seagrasses:

Assessment and Management Options

F.J. Sargent, T.J. Leary, D.W. Crewz and C.R. Kruer

FLORIDA MARINE RESEARCH INSTITUTE

TECHNICAL REPORTS
Lawton Chiles

Governor of Florida

Florida Department of Environmental Protection

Virginia B. Wetherell

Secretary

The Florida Marine Research Institute (FMRI) is a bureau of the Florida Department of

Environmental Protection (FDEP). The FDEP’s mission is to “protect, conserve, and manage

Florida’s environment and natural resources.” The FMRI conducts applied research pertinent to

managing marine-fishery resources and marine species of special concern in Florida.

Programs at the FMRI focus on resource-management topics such as managing gamefish and

shellfish populations, restoring depleted fish stocks and the habitats that support them, protecting coral reefs, preventing and mitigating oil-spill damage, protecting endangered and threatened

species, and managing coastal-resource information.

The FMRI publishes three series: Memoirs of the Hourglass Cruises, Florida Marine Research

Publications, and FMRI Technical Reports. FMRI Technical Reports contain information relevant to

immediate resource-management needs.

Kenneth D. Haddad, Chief of Research

Institute Editors

Theresa M. Bert, David K. Camp, Paul R. Carlson, Mark M. Leiby,

William G. Lyons, Anne B. Meylan, Robert G. Muller, James F. Quinn, Jr.,

Ruth O. Reese, Carmelo R. Tomas

Judith G. Leiby, Copy Editor
Scarring of Florida’s Seagrasses:

Assessment and Management Options

Frank J. Sargent, Timothy J. Leary, David W. Crewz

Florida Department of Environmental Protection

Florida Marine Research Institute

St. Petersburg, FL

and

Curtis R. Kruer

Consulting Biologist

Summerland Key, FL

Florida Department of Environmental Protection

FMRI Technical Report TR-1

1995
Cover Photograph

Northwest of Windley Key in the Florida Keys.

Photograph by Curtis R. Kruer, 1993.

Copies of this document may be obtained from

Florida Marine Research Institute

100 Eighth Ave. SE

St. Petersburg, FL 33701-5095

Attn: Librarian

Document Citation

Sargent, F.J., T.J. Leary, D.W. Crewz, and C.R. Kruer. 1995. Scarring of Florida’s seagrasses: assessment and management options. FMRI Tech. Rep. TR-1. Florida Marine Research

Institute, St. Petersburg, Florida. 37 p. plus appendices.

Document Production

This document was designed in Microsoft Word (v. 5.1a) and formatted using Quark

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The document was designed by the authors, and McShane and Moore Communications,

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printed the document.

The text paper used in this publication meets the minimum requirements of the American

National Standard for Permanence of Paper for Printed Library Materials Z39.48—1992.
Table of Contents

LIST OF TABLES ........................................................................................................................................ ii

LIST OF FIGURES ..................................................................................................................................... iii

ACKNOWLEDGMENTS .............................................................................................................................. iv

EXECUTIVE SUMMARY .............................................................................................................................. v

INTRODUCTION ......................................................................................................................................... 1

Seagrass Recovery ...................................................................................................................... 5

Study Objectives ........................................................................................................................ 7

METHODS ................................................................................................................................................. 7

Scarring Recognition................................................................................................................... 9

Scar Mapping............................................................................................................................ 10

RESULTS .................................................................................................................................................. 12

DISCUSSION ............................................................................................................................................ 24

MANAGEMENT OPTIONS ........................................................................................................................ 29

Four-Point Approach ............................................................................................................... 31

Education ......................................................................................................................... 31

Channel Marking (Aids to Navigation) ........................................................................ 31

Enforcement ..................................................................................................................... 32

Limited-Motoring Zones ............................................................................................... 32

CONCLUDING REMARKS ........................................................................................................................ 33

LITERATURE CITED ................................................................................................................................. 35

APPENDIX A ........................................................................................................................................... 39

Methodology for Analyzing Scar Data .................................................................................... 41

MRGIS Integration ......................................................................................................... 41

Creating a Statewide Seagrass Coverage .................................................................... 41

Error Reduction ............................................................................................................... 43

APPENDIX B ........................................................................................................................................... 45
ii

List of Tables

Table 1. NOAA/USGS charts.....................................................................................................13

Table 2. Acreage of scarred seagrasses by county ..................................................................14

Table 3. Relative percentage of scarred seagrasses by county ..............................................15

Table 4. Within-county percentage of scarred seagrasses......................................................17

Table 5. Ranking of scarred-seagrass acreage by county.......................................................18

Table 6. Components of seagrass acreage in Monroe and Dade counties .........................19

Table 7. Scarred-seagrass acreage by region ...........................................................................19

Table 8. Moderately scarred sites in lower Florida Keys.......................................................25

Table 9. Severely scarred sites in lower Florida Keys ............................................................26

Table 10. Vessel registrations by county .....................................................................................27

Table 11. Vessel registrations by region......................................................................................28

APPENDIX A

Appendix Table 1. Sources of seagrass data.........................................................................................42
iii

List of Figures

Figure 1. Seagrass species of Florida ......................................................................................... 2

Figure 2. Aerial view of scarred seagrasses—Lignumvitae Key, Florida Keys................... 4

Figure 3. Seagrass rhizome differentiation ............................................................................... 5

Figure 4. Study area for assessment of seagrass scarring ...................................................... 8

Figure 5. Example of polygon delineation.............................................................................. 10

Figure 6. Diagrams of scarring-intensity categories.............................................................. 11

Figure 7. Recognition of scarring intensity............................................................................. 12

Figure 8. Regions of Florida analyzed for scarred seagrasses............................................. 20

Figure 9. Detailed map of scarred seagrasses—Pine Island, Lee County.......................... 22

Figure 10. Detailed map of scarred seagrasses—Windley Key, Monroe County ............... 23

Figure 11. Example of channels ending in shallow seagrass beds ....................................... 30

APPENDIX B

Figure B1. Scar-distribution map—Escambia, Santa Rosa, Okaloosa counties

Figure B2. Scar-distribution map—Walton, Bay, Gulf counties

Figure B3. Scar-distribution map—Franklin, Wakulla, Jefferson counties

Figure B4. Scar-distribution map—Taylor, Dixie counties

Figure B5. Scar-distribution map—Levy, Citrus, Hernando counties

Figure B6. Scar-distribution map—Pasco, Pinellas, Hillsborough counties

Figure B7. Scar-distribution map—Manatee, Sarasota, Charlotte counties

Figure B8. Scar-distribution map—Lee, Collier counties

Figure B9. Scar-distribution map—Monroe County 

Figure B10. Scar-distribution map—Dade, Broward counties

Figure B11. Scar-distribution map—Palm Beach, Martin counties

Figure B12. Scar-distribution map—St. Lucie, Indian River counties

Figure B13. Scar-distribution map—Brevard, Volusia counties
iv

Acknowledgments

This research was partially funded under a Coastal Zone Management grant pursuant to National Oceanic and Atmospheric Administration Award No. NA170Z0501.

A number of people deserve special recognition for their contributions to this research: Chris

Friel, Henry Norris, Jim Poehlman, and Bill Sargent in the Coastal and Marine Resources

Assessment (CAMRA) group at the FMRI were substantially involved in the design, input and

output, field-survey, and editing aspects of this project.

Special thanks are also extended to Lt. Mike Wood, Florida Marine Patrol, for his patience during the aerial surveys and to Randolph L. Ferguson, National Marine Fisheries Service (NOAA),

and Roy R. Lewis, III, Lewis Environmental Services, Inc., for manuscript review.

We also thank the following people for their assistance:

Everglades National Park: Skip Snow

Florida Department of Environmental Protection, Division of Law Enforcement, Florida Marine Patrol:

C. B. Goldacre, Fred Klohn, Lt. Steve Stout, and Lt. Paul Whitley

Florida Department of Environmental Protection, Division of Marine Resources, Florida Marine Research

Institute: Bredin Cummings, Sandra Drumm, Mike Durako, Ken Haddad, John Hunt, Chuck

Idelberger, Gail MacAulay, Tom Matthews, Bob McMichael, Mike Mitchell, Jim Quinn, and

Linda Tripodo

Florida Department of Environmental Protection, Division of State Lands, Aquatic Preserves:

Brian Poole, Kalani Cairns, Matthew Clemons, John Hughes, Judith Ott, Robert Repenning,

Bradford Rieck, and Heather Stafford 

Monroe County: Virginia Barker and George Garrett

South Florida Water Management District: Patti Sime and Les Vilcheck

Southwest Florida Water Management District: Steve Dicks, Hugh Dinkler, Bob Evans, and Tom Lo

St. Johns River Water Management District: Bob Virnstein

Tampa Bay Regional Planning Council: Peter Clark

University of South Florida, New College: Ruth Folit and Julie Morris
Scarring of Florida’s Seagrasses:

Assessment and Management Options

Executive Summary

Seagrasses are submerged, grass-like plants that

inhabit the shallow coastal waters of Florida.

Seagrasses are a vital component of Florida’s

coastal ecology and economy; they provide nutrition and shelter to animals important to marine

fisheries, provide critical habitat for many other

animals (e.g., wading birds, manatees, and sea turtles), and improve water quality.

Marine-habitat degradation in Florida is continuing at an alarming rate as the coastal residential population and the number of seasonal visitors

increase. Habitat degradation has many sources

(e.g., pollution, dredge and fill), but an increasingly common cause of habitat degradation is the

scarring of seagrasses. In this report, scarring can

refer to either the activity of scarring or to a group

of scars in a seagrass bed. Seagrass beds can be

scarred by many activities, but scars are most commonly made when a boat’s propeller tears and cuts

up roots, stems, and leaves of seagrasses, producing a long, narrow furrow devoid of seagrasses.

Boats operating in shallow waters are severely

scarring, and sometimes completely denuding,

seagrass beds throughout the state.

The Florida Department of Environmental

Protection recognized the need to reduce scarring

of seagrasses by boats and committed resources to

address this issue. As one component of this effort,

the Florida Marine Research Institute (FMRI)

investigated the distribution of scarred seagrass

beds in the shallow marine waters of Florida’s

coastal counties. Aerial photography was used to

locate seagrass scarring. Aerial surveys were then

conducted in 1992–1993 to confirm the location of

scarred seagrasses. We did not attempt to distinguish among the different specific causes of seagrass scarring. During aerial surveys, observations

of scarred seagrasses were recorded on National

Oceanic and Atmospheric Administration nautical

charts and U.S. Geological Survey quadrangle

maps.

Scarring intensity was categorized as light,

moderate, or severe. Areas with substantial scarring

recognizable on 1:24,000-scale photography were

delineated on the maps with polygons, which

were assigned a scarring intensity. Polygons categorized as light contained less than 5 percent scarring, those categorized as moderate contained 5–20

percent scarring, and those categorized as severe

contained more than 20 percent scarring. The

information acquired in this survey was incorporated into the FMRI’s Marine Resources

Geographic Information System (MRGIS), which

produces maps and tabular products so that geographically based data can be effectively disseminated to resource managers, appropriate regional

and county governments, and other interests (e.g.,

conservation groups and private citizens).

Scarred seagrasses were observed in all areas

of the state, mostly in shallow coastal waters less

than six feet deep. More than 173,000 acres of the

state’s 2.7 million acres of seagrasses were

scarred—most of it lightly. This is a conservative

estimate of scarring because we mapped groups of

scars, not isolated, individual propeller scars. The

total seagrass acreage in Florida (2.7 million acres)

includes areas in the Florida Keys that have sparse

seagrass and hardbottom with dense-seagrass

patches. Excluding these areas, seagrasses totaled

approximately 1.9 million acres. Also, these totals

do not include sparse, deep Halophila beds that are

offshore in the Big Bend region.

The greatest acreage of moderate and severe

(M/S) scarring occurred in areas having denser

human populations and more registered boats.

The Florida Keys (Monroe and Dade counties),

Tampa Bay (Hillsborough, Manatee, and Pinellas

counties), Charlotte Harbor (Lee County), and the

north Indian River Lagoon (Brevard and Volusia

counties) had the greatest M/S scarring. Monroe

County, which includes most of the Florida Keys,

had the greatest acreage of M/S scarring of all

counties in the survey. The Panhandle and Big

Bend regions had little M/S-scarred acreage, but in

the western Panhandle embayments, M/S scarring

was prevalent in the few acres of seagrasses there.

If an area has little seagrass acreage, then any scarring may have a critical effect on habitat functions.
Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Executive Summary FMRI Technical Report TR-1

All boating user-groups are responsible for

scarring seagrasses. Although we did not attempt

to identify each user-group’s role in scarring, we

believe general statements about the situations

that lead to scarring are valid. The most severe single instances of scarring are caused by large commercial vessels, but most seagrass disruption

results from widespread scarring by smaller boats.

Our discussions with boaters, as well as our own

personal experiences, suggest that scarring of seagrasses could result when one or more of the following situations occur: 

• when boaters misjudge water depth and accidentally scar seagrass beds; 

• when boaters who lack navigational charts or

the skill to use them stray from poorly marked

channels and accidentally scar seagrass beds; 

• when boaters intentionally leave marked channels to take shortcuts through shallow seagrass

beds, knowing that seagrass beds may be

scarred; 

• when boaters carelessly navigate in shallow

seagrass beds because they believe scars heal

quickly; 

• when inexperienced boaters engage in recreational and commercial fishing over shallow

seagrass flats, thinking that their boat’s

designed draft is not deep enough to scar seagrasses or that the design will prevent damage

to their boat;

• when boaters overload their vessels, causing

deeper drafts than the boaters realize;

• when boaters anchor over shallow seagrass

beds, where their boats swing at anchor and

scar seagrasses; 

• when boaters intentionally prop-dredge to create a channel; and

• when inexperienced boaters, ignorant of what

seagrasses are and the benefits they provide,

accept as the behavioral norm local boating customs that disregard the environment.

Management programs that address scarring

of seagrasses should be based on an approach that

involves (1) education, (2) channel marking,

(3) increased enforcement, and (4) limited-motoring zones. Aerial monitoring and photography of

the managed area are essential in evaluating the

effectiveness of a program. Management programs

that use this multifaceted approach have been

instituted by a few local governments and at several state parks. Initial results of the programs

indicate that in some areas seagrass scarring has

been reduced but that in other areas emphasis may

need to be increased on one or more of the components of the four-point approach. A statewide

management plan is needed to address the most

egregious scarring over large areas that may be

difficult to regulate at the local-government level.
Scarring of Florida’s Seagrasses:

Assessment and Management Options

Introduction

Seagrasses are completely submerged, grass-like

plants that occur mostly in shallow marine and

estuarine waters. Seagrasses form small, patchy

beds if their seedlings have recently colonized bare

sediments or if sediment movement or other disturbances disrupt typical growth patterns. Where

disturbances are minimal and conditions promote

rapid growth, large continuous beds—known as

meadows—may develop when patchy seagrass

beds coalesce. Seagrass meadows may require

many decades to form. In shallower waters of

good quality, seagrass meadows may be lush and

have a high leaf density, but in deeper waters, they

may be sparse, or species composition may shift to

a less robust species.

The predominant seagrass species in Florida

(Figure 1) are turtle-grass (Thalassia testudinum

Banks ex Koenig), shoal-grass (Halodule wrightii

Aschers.), and manatee-grass (Syringodium filiforme

Kutz.). Other, less common, seagrasses—star-grass

(Halophila engelmannii Aschers.), paddle-grass

(Halophila decipiens Ost.), Johnson’s seagrass

(Halophila johnsonii Eisem.), and widgeon-grass

(Ruppia maritima L.)—may be locally abundant.

Near river mouths subject to salinity fluctuations,

other submerged aquatic plant species (e.g.,

Zannichellia sp. and Najas spp.) may occupy an ecologic role similar to that of the true marine seagrasses. Nevertheless, these species are rarely considered part of the seagrass flora of Florida.

Turtle-grass is the largest of Florida’s seagrass

species, and Johnson’s seagrass is the most

diminutive. Johnson’s seagrass was only recently

recognized and named as a distinct species

(Eiseman and McMillan 1980). Unlike the other

species, which are widespread in Florida,

Johnson’s seagrass is limited to scattered locations

in the lagoonal river systems of Florida’s Atlantic

coast. Because of its fragile nature, restricted distribution, and vulnerable status in the lagoonal systems (from development), Johnson’s seagrass has

been nominated for federal listing as a threatened

species under the Endangered Species Act of 1973.

The wide distribution and robust nature of

turtle-grass belie its susceptibility to stress. Turtlegrass’s tolerances, in respect to some environmental factors, are less developed than are those of

some of the other seagrass species. Shoal-grass and

widgeon-grass, for instance, are much more tolerant of periodic exposure during extremely low

tides and consequently can flourish in shallower

water than turtle-grass can. Manatee-grass has

wiry leaves—round in cross section—that are

more tolerant of strong currents. Like turtle-grass,

manatee-grass is less tolerant of exposure and is

often found mixed with turtle-grass at depths that

are rarely exposed at extremely low tides. Species

of Halophila are generally more tolerant of lower

light conditions and usually form sparse beds in

deeper waters, especially in the Gulf of Mexico offshore of Florida’s Big Bend region.

The numerous plants and animals that live

and grow among seagrasses form a complex, fragile community. Marine and estuarine animals—

especially larval and juvenile fish—benefit from

seagrasses, which provide critical shelter and sustenance. Seagrasses form some of the most productive communities in the world (Zieman and

Zieman 1989) and are aesthetically and economically valuable to humans. Seagrasses are a principal contributor to the marine food web and ultimately provide humankind with much of its

seafood (Thayer et al. 1975). In addition, seagrasses improve water quality by stabilizing mobile

sediments and by incorporating some pollutants

into plant biomass and into the stabilized sediments.

As Florida’s population increases, particularly

in coastal counties, threats to seagrass communities increase (Livingston 1987). Seagrass losses in

Florida have been documented to range from 30

percent in the Indian River Lagoon (Haddad and

Harris 1985) to 81 percent in Tampa Bay (Lewis et

al. 1985). The cumulative effects of anthropogenic

threats (e.g., water pollution, docks, dredging and

filling) are being addressed by various federal,

state, and local resource management programs.

One threat that is becoming more acute—as people

increasingly use boats andother watercraft for

recreation and work—is scarring of seagrasses. In
2 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Syringodium filiforme

Manatee-grass

Ruppia maritima

Widgeon-grass

Halophila decipiens

Paddle-grass

Halophila johnsonii

Johnson's Seagrass

Halophila engelmannii

Star-grass

Thalassia testudinum

Turtle-grass

Halodule wrightii

Shoal-grass

Figure 1. Seagrass species occurring in the shallow coastal waters of Florida 

(based on drawings by Mark D. Moffler).
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 3

this report, scarring can refer to either the activity

of scarring or to a group of scars in a seagrass bed.

Boat propellers scar seagrasses more often than do

other sources.

Most scarring of seagrasses is caused by smallboat propellers; however, larger craft, which are

usually confined to deeper waters, may have much

larger individual effects when they run aground,

especially near shipping channels and ports.

Propeller scarring of seagrasses was commented

on in the scientific literature as early as the late

1950s (Woodburn et al. 1957, Phillips 1960).

Concern has occasionally been voiced since then

(e.g., U.S. Dept. of the Interior 1973, Chmura and

Ross 1978). Eleuterius (1987) noted that scarring in

Louisiana seagrasses was common and in deeper

water was caused by shrimp boats, which also

ripped up the margins of the beds with their

trawls. Shrimper-related scarring and seagrass

damage were also recognized by Woodburn et al.

(1957).

Usually, propeller scarring of seagrasses

occurs when boaters motor through water that is

shallower than the drafts of their boats. The propellers tear and cut up seagrass leaves, roots,

stems, and sediments, creating unvegetated, lightcolored, narrow furrows called prop scars. In some

areas, watercraft have extensively scarred seagrass

beds, which has alarmed environmentally concerned citizens (Wilderness Society et al. 1990). In

the Florida Keys, for example, as waterfront and

recreational development has increased since the

1970s, so has the number, size, and power of vessels in this region—resulting in widespread, and in

some cases severe, scarring of shallow seagrass

communities. Nearly all shallow seagrass beds in

Florida show some degree of scarring. Portions of

seagrass beds throughout the state have been completely denuded by repeated scarring (Figure 2).

The degree of scarring depends, among other

things, on the interaction between water depth and

the size, kind, and speed of the boat. Vessels with

more than one motor can have a much greater single-event effect on seagrasses than do singlemotored (and usually smaller) vessels. Several parallel tracks through a seagrass bed are a strong

indicator that a multiple-motored vessel has probably passed that way. At lower tides, seagrass beds

are more susceptible to scarring, even from a boat

that would not scar them at higher tides. At high

tide, a boat may navigate safely over seagrasses

without scarring them, but at medium to low tide

on the return trip, the same boat may scar them. A

smaller boat operating at a slow speed or powering up may scar seagrass beds that would not be

scarred after the boat reaches a plane.

A boater’s attitude is another factor that may

influence the degree of scarring. Sometimes

boaters are aware of but unconcerned about seagrasses and therefore do not avoid scarring them;

A conscientious boater who trims his motor may

only scar seagrasses slightly when he inadvertently enters a bed. A more extreme form of scarring

occurs when a boater intentionally uses the boat’s

propeller as a dredge to remove seagrasses and

sediments to produce a channel so that the boater

can have easier access to other areas. This is called

prop-dredging, and in some areas, it has permanently prohibited seagrass recovery, especially if

sediments were dredged to bare rock. Currently,

prop-dredging is illegal (see U.S.A. and FDER v.

M.C.C. of Florida and Michael’s Construction

Company, Case No. 81-2373-CIV-EBD, Southern

District of Florida) but is difficult to enforce.

Although everyday boating activities—which may

repeatedly scar seagrasses over extensive areas—

are more difficult to control because they are less

overt, they may ultimately do greater harm to

overall seagrass productivity than prop-dredging

alone does.

Substantial scarring of shallow seagrass beds,

which are critical feeding and sheltering areas 

for wading birds, juvenile finfish, and shellfish,

results in a cumulative reduction of productive

habitat. Extensive scarring may expose the beds to

further disruption from storms and other natural

erosional forces, thereby increasing the rate of

cumulative loss. This can result in the resuspension of sediments in the water column, which may

further contribute to habitat loss by inhibiting the

growth of seagrasses. Location and species composition of seagrass beds are probably principal

determinants of the kind of animal habitat lost to

scarring; however, comprehensive data do not

exist concerning animal distributions in most 

seagrass areas of Florida.
4 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Figure 2. Aerial view of seagrass-bed scarring at Lignumvitae Key in the Florida Keys.
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 5

Seagrass Recovery

Seagrass scarring has received limited study since

the 1970s (e.g., Godcharles 1971, Zieman 1976),

and only recently, as scarring has increased, has

research become more focused on scar recovery

(e.g., Matthews et al. 1991, Durako et al. 1992).

Research on many aspects of seagrass biology and

ecology has contributed greatly to our ability to

protect marine resources. This research has shown

that each of Florida’s seagrass species has structural and physiological differences that affect their

growth characteristics, stress tolerances, and ecologic contributions. As with other elements of seagrass ecology, scar recovery differs for each of the

seagrass species.

Seagrass species differ in their growth 

forms, particularly in the relationship between

their rhizomes (underground stems) and leaves

(Duarte et al. 1994). Some seagrass species’ rhizomes are weakly differentiated for vertical

growth, and these plants may be more vulnerable

to burial by mobile sediments. Other species 

(especially turtle-grass) have more strongly developed vertical rhizomes (i.e., short-shoots) and so

can withstand some sedimentation (Figure 3).

Because of this differentiation, branching and 

lateral growth are usually slower in species with

the latter morphology, and scar recovery is 

also likely to be slower. Zieman (1976) attributed

slow recovery of scars in turtle-grass beds to

unsuitable sediment quality, damaged rhizomes,

and the naturally slow growth of rhizome tips. 

He suggested that shoal-grass recovers more

quickly than turtle-grass does because shoalgrass has a shallower rhizome system and grows

well from seed. Also, shoal-grass probably recovers faster because its rhizomes have a greater 

density of short-shoots and nodes—from which

lateral branching occurs—than does turtle-grass

(Durako et al. 1992).

Figure 3. Gradient of horizontal and vertical rhizome differentiation in different seagrass

genera, from those with no differentiation to those that only have leaves on the vertical

rhizomes (after Duarte et al. 1994). Species within genera may differ in form. Gradient does

not imply a phylogenetic relationship.

DIFFERENTIATION OF VERTICAL RHIZOME

No vertical

rhizomes

Branches grow

vertically or

horizontally

Short-shoots, but still

with horizontal leaves

Leaves only on

short-shoots

Zostera Posidonia Halodule

Syringodium

Thalassia
6 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Studies in which trenches were cut 6 to 18

inches deep into seagrass beds indicated that seagrasses may recover slowly from scarring (Jones

1968 cited in Zieman 1976, Godcharles 1971). The

trenches readily refilled with sediment, but seagrass regrowth was minimal even after two years.

Zieman (1976) found that turtle-grass may require

at least two years to begin to recolonize scars; even

after five years, some scars were still visible. In a

more recent study, Durako et al. (1992) used a linear-regression model to predict that individual

scars 0.25 m wide cut into the centers of shoalgrass beds require 0.9–1.8 years to recover to a normal density (2000–4000 short-shoots/m2) but that

turtle-grass takes approximately 3.6–6.4 years to

achieve normal density (400–700 shortshoots/m2). At the sparser edges of shoal-grass

beds, however, recovery times (2.3–4.6 years)

approached those of turtle-grass, probably because

of lower nodal densities at the margins of shoalgrass beds. Some researchers have indicated that

complete seagrass-scar recovery may take as long as

ten years, depending on the size of the denuded

area (Lewis and Estevez 1988). For seagrass to

recover in the shortest period, scarred areas must

remain free of additional scarring, and other environmental conditions must be favorable for plant

survival and growth. Even so, the recovery period

for scarred seagrass beds (especially for turtlegrass) averages at least three to five years and is

probably much longer in areas of poor water quality and where scarring is severe and repetitive.

Some scarred seagrass beds may never recover.

The rate of seagrass recovery from scarring

depends on many factors. Some of the variables

that may affect recovery from scarring are sediment composition, water quality, current velocity,

wave and wind energy, drift algae, scar depth, seagrass species, water depth, and latitude. Sediment

properties and water quality are overriding determinants of recovery from scarring. Seagrasses

absorb nutrients from the sediments in which they

are rooted and also derive nutrition from the water

column. Durako et al. (1992) suggested that south

Florida sediments, which are usually carbonaceous marl muds, could affect seagrass regrowth

differently than do the predominantly quartz-sand

sediments of Tampa Bay. Over short distances,

sediment quality may vary significantly; sediments in scars can differ in quality even from adjacent, undisturbed seagrass sediments. In the

Florida Keys, for example, soil particle sizes were

coarser in scars, and sediments had a lower pH

and EH (Zieman 1976). In Tampa Bay, by contrast,

particle-size distributions did not differ between

scars and adjacent seagrass sediments (Dawes et

al. 1994). Therefore, sediment type and other local

conditions may affect whether scar sediments differentiate from adjacent unscarred seagrass sediments.

Water quality (e.g., salinity and clarity) affects

plant physicochemical attributes such as osmotic

balance and photosynthetic rates and, therefore, it

can affect the amount of energy available for seagrass growth. Some seagrass species tolerate much

lower salinities than others do. Turtle-grass, for

example, does not survive for long in salinities

below 20–25 parts per thousand (Lewis et al. 1985,

Dawes 1987). Although Eleuterius (1987) observed

that widgeon-grass could withstand totally fresh

water, he found that of the truly marine seagrasses, shoal-grass was the most tolerant of low salinities and star-grass was the least tolerant. Turtlegrass and manatee-grass were intermediate in

their responses to lower salinity. In areas where

frequent and large freshwater pulses are common

(e.g., near the mouths of rivers), recovery rates will

be faster in seagrass species that tolerate lower

salinities (i.e., shoal-grass and widgeon-grass).

Shading experiments and surveys of seagrass

extents in turbid waters have shown that light

reduction lowers shoot density and reduces survivability (Hall et al. 1991, Onuf 1991). Sediments

that are composed mainly of finer particle sizes are

more subject to resuspension (Gucinski 1982) and

could pose a threat to photosynthetic processes in

seagrasses. Sediment resuspension and water clarity are affected by current velocity, wave and wind

energy, and nutrient fluxes, among other things. In

particular, drift algae may respond vigorously to

higher nutrient levels and depress scarring-recovery rates by physically inhibiting seagrass growth

(e.g., Holmquist 1992) and photosynthesis and by

accumulating in scars.

Water depth influences photosynthetic rates

and seagrass growth, especially in nutrient-rich

waters. Seagrasses in deeper water receive lower

amounts of solar radiation and a different quality

of light, both of which could affect energy-allocation patterns. Energy-allocation patterns of seagrasses can also be affected by latitude. Latitude,

coupled with other local environmental variables,
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 7

affects seagrass growth because of differing watertemperature, solar-incidence, and day-length

regimes. The warmer water, longer day-lengths,

and more intense solar radiation occurring at

lower latitudes probably enhance seagrass growth

rates and fruit production in deeper or more turbid

water. Therefore, potential recovery and recolonization rates may be faster for seagrasses in the

Florida Keys than in the Florida Panhandle.

However, local physicochemical conditions, such

as sediment characters, may override latitudinal

effects.

Scar depth probably affects regrowth rate as

well. Deeper scars may not fill with sediment, or

may become enlarged, if they occur in areas of

strong currents (Zieman 1976, Eleuterius 1987).

Scars in shallow-water seagrass beds that are

exposed to long wind fetches may be scoured by

strong winds and waves, especially during extremely low tides. Boat wakes can also scour

scarred areas. Kenworthy et al. (1988) concluded

that boat-wake waves substantially elevate bottom-shear stress along shallow seagrass beds and

seriously jeopardize seagrass health.

Study Objectives

Slow recovery from scarring, coupled with increased scarring rates, elevates the rate of cumulative loss of seagrasses and their habitat values.

Concerns about the effects of seagrass scarring and

recovery on marine productivity compelled the

Florida Marine Research Institute (FMRI) to survey the extent and intensity of scarring in the shallow coastal waters of Florida. Information from

this general study is intended to assist government

agencies with developing specific management

programs in regard to boat-generated scarring of

seagrasses.

A general survey of the extent and intensity of

scarring is the necessary first step in developing

appropriate and cost-effective management protocols. This report identifies and quantifies the

extent of scarred seagrass beds throughout most of

Florida. We collected and analyzed the data using

a combination of aerial photography, aerial surveys, and Geographic Information System (GIS)

technology. For the first time, the statewide extent

of seagrasses is described, and the magnitude of

scarring is estimated and documented so that

Florida’s seagrass resources can be more effectively protected. Based on the data and anecdotal

observations generated in this study, we identify

and discuss behavioral activities and navigational

circumstances that exacerbate seagrass scarring.

Further investigations and surveys using developing technologies will refine our knowledge of seagrass distributions and the effects of human activities on the resource’s productivity.

Methods

The main goal of this project was to survey

Florida’s shallow marine and estuarine waters for

scarring of seagrasses. For most of Florida, we

used an approach combining analysis of high-resolution aerial photographs with ground-truthing

during aerial surveys. In the Florida Keys, the aerial surveys were conducted first, and aerial photography was used as collateral data.

The study area extended from the AlabamaFlorida border at Perdido Bay (Escambia County),

east and south along the Gulf coast to the Florida

Keys, and then north along the lagoonal river systems of the Atlantic Coast to just south of New

Smyrna Beach (Volusia County) in Mosquito

Lagoon. A total of 31 of the state’s 35 coastal counties are included in this survey (Figure 4). The four

counties north of Volusia County on the Atlantic

coast of Florida were not included because areas

suitable for seagrass growth are not present. Only

the southern part of Volusia County below U.S.

Highway A1A at Port Orange was included in this

survey.

Even though seagrass scars can result from

many sources (e.g., ship groundings, live-aboard

houseboats, and even four-wheel-drive vehicles),

boat propellers are the most widespread cause of

scarring. In this study, we did not distinguish

among the various scarring sources. Individual

prop-scar widths are narrow and average approximately 12 inches; scar lengths vary considerably,

from miles to only yards long and can be difficult

to see in aerial photographs. In a previous study of

scar recovery, Durako et al. (1992) suggested that

the smallest-scale (least detailed) aerial photography useful for recognizing scars in seagrass beds is

1:24,000 (1 inch = 2,000 ft). A greater number of

scars can be identified using larger-scale photography (e.g., 1:2,400). At a single site in Tampa Bay,

Durako et al. (1992) were able to distinguish 700

individual scars in 1:2,400-scale photography, 104
8 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Okaloosa

Gulf

Dixie

Levy

Volusia

Citrus

Brevard

Pasco

Pinellas

St. Lucie

Martin

Palm Beach

Collier Broward

Dade

Escambia

Santa Rosa

Walton

Jefferson Bay

Wakulla

Taylor Franklin

Hernando

Hillsborough

Manatee

Charlotte

Lee

Indian River

Sarasota

Monroe

Alabama Georgia

Gulf

of

Mexico

Atlantic

Ocean

E

N

W

S

Figure 4. Study area for assessment of seagrass scarring.
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 9

scars at 1:12,000, and only 5 scars with 1:24,000.

Nevertheless, they suggested that most of the

heavily scarred areas could be identified at the

1:24,000 scale and that the trade-off in the time

saved using 1:24,000 photography justified its use.

Even though aerial photography can provide

sufficient detail to allow recognition of prop scars,

high-detail photography is often limited to certain

areas. Pertinent photography not contained in the

FMRI library was obtained from the appropriate

water-management districts. The largest-scale aerial photography available was 1:13,200 colorinfrared (CIR) transparencies made for the Florida

Keys Land Cover Mapping Project (funded by the

U.S. Environmental Protection Agency’s Advanced Identification of Wetlands Program) in

December 1991. The smallest-scale photography

used to delineate scarring in our study consisted of

1:40,000 CIR transparencies provided by the South

Florida Water Management District (SFWMD).

These photographs covered Hobe Sound, southeast Florida, Biscayne Bay, the upper Florida Keys

and Florida Bay, and the southwest region of

Florida from Florida Bay to Charlotte Harbor. The

Southwest Florida Water Management District

(SWFWMD) supplied 1:24,000 CIR photographs

from Yankeetown south to Charlotte Harbor. The

St. Johns River Water Management District (SJRWMD) furnished 1:24,000 CIR photographs for

Mosquito Lagoon and Indian River Lagoon. The

only aerial photographs available for the

Panhandle and Big Bend regions were approximately ten years old and therefore were too dated

for delineating seagrass scarring for this study. The

oldest photographs used for scarring delineation

were taken in November 1990. Although these

photographs did not represent conditions at the

time of the survey, historical scarring patterns

were documented from them, and areas requiring

closer examination were identified.

Some problems are inherent in using photography of different scales. In particular, comparing

maps of different scales should be done with caution. Large-scale photography (e.g., 1:2,400) can

give more accurate representations of seagrass distributions and scarring than smaller-scale (e.g.,

1:40,000) photography can. Just the width of a line

drawn on a small-scale photograph may contain

many hundreds or thousands of acres of seagrass,

depending on the line’s length and the scale of the

photography. One problem in implementing this

study was that large-scale photography—or even

photography of the same scale for different areas

of the state—did not exist. Also, offshore county

lines were based upon 1:100,000 TIGER cultural

data, and subtle differences in county-line boundaries could alter conclusions if the data are used

too strictly in detailed comparisons. Therefore, we

urge caution when making comparisons of the differences between regions and between counties.

Scarring Recognition

Scarring was recognized as distinct areas of lightcolored lines and patches—visible in photographs

and from the air—that contrasted with the darker

colors of seagrass beds. Scarred areas in the 9 inch

x 9 inch CIR aerial photographs were delineated

using binocular macroscopes and stereoscopes,

and the delineations were transferred to registered

acetate overlays. Where scars merged, a bounding

polygon was drawn around the entire scarred area

(Figure 5). Polygons were only drawn around

groups of scars, not around single, isolated prop

scars. We did not map areas less than one acre due

to the small-scale maps used. Because of the mapping procedure and differing map scales used, we

may have inadvertently included small portions of

bare substrate, channels, and open water in some

polygons. For example, in areas that contained

intricate shorelines with numerous islands—such

as the Ten Thousand Islands and the Chassa-howitzka and Crystal rivers—delineating small polygons was impossible at the available map scales; as

a consequence, some unscarred areas were incorporated within the polygons.

The intensity of scarring in each polygon was

categorized based upon the Comparison Chart for

Visual Estimation of Percentage Composition

(after Terry and Chilingar 1955). Polygons designated as light enclosed areas where less than 5 percent of the seagrasses were scarred, moderate

polygons contained areas with from 5 percent to 20

percent scarring, and severe polygons delineated

areas with more than 20 percent scarring. For

example, a 20-acre polygon that was classified as

being moderately scarred would contain between

1 and 4 acres of actual scars. Diagrammatic representations of the three categories of estimated scarring intensity are shown in Figure 6. In some areas,

different intensities of scarring were adjacent and

could not be easily differentiated. These areas were

delineated as a single polygon and were assigned
10 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

a value for the overall scarring intensity. An

oblique aerial photo in Figure 7 illustrates this situation.

Information about seagrass scarring in Florida

Bay was furnished by Skip Snow of the Everglades

National Park (ENP). Within Florida Bay, scarring

occurs principally on seagrass banks, which are

exposed at low tide. To confirm the locations of

scarred seagrasses, a brief aerial survey was conducted by FMRI staff over a portion of Florida Bay.

Polygons drawn on the registered overlays on

the aerial photographs were transferred to

National Oceanic and Atmospheric Administration (NOAA) nautical charts using a zoom transfer

scope (ZTS). The ZTS superimposes an image onto

a base map of a different scale, providing for accurate transfer of the hand-drawn polygons from the

photograph overlays onto the NOAA base maps.

In most cases, 1:40,000-scale NOAA charts were

used as base maps. The lack of larger-scale charts

for the region from Anclote Key (Pasco County) to

Alligator Harbor (Franklin County) forced us to

use 1:80,000-scale charts. When possible, we used

inset maps of various scales (1:5,000–1:20,000) to

supplement small-scale chart information. In a

portion of the Florida Keys, 1:24,000-scale U. S.

Geological Survey (USGS) quadrangle maps were

used as base maps because the largest-scale

NOAA charts were only available at a scale of

1:80,000 (Table 1).

Scar Mapping

After marking the maps and charts with polygons,

we conducted aerial surveys to verify scarring and

refine the delineations of scarring intensity. Most

aerial surveys were conducted between May 1992

and May 1993. The Florida Keys surveys were conducted between October 1992 and March 1993.

Aerial surveys were important in assuring accurate representations of the extent and intensity of

scarring because even in the better photographs,

not all scars were visible. During the aerial surveys, boats were frequently observed scarring

shallow seagrass beds. Some of these events were

photographed, and the photographs were deposited in the FMRI library. 

Figure 5. Example of polygon delineation.

Severe-Scarring Polygons Severe-Scarring Polygons
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 11

The Indian River Lagoon, the southeast

Intracoastal Waterway, and the Florida Keys were

surveyed from light, fixed-wing aircraft (Cessna

152 or 172) in regions where seagrasses were distributed along relatively straight and continuous

shorelines. Regions with convoluted shorelines

and numerous islands, such as Tampa Bay,

Biscayne Bay, Waccasassa Bay, and parts of Florida

Bay, were surveyed from a helicopter (Hughes

500). In the lower Florida Keys, where wide areas

of seagrass extend from the Atlantic Ocean into

Florida Bay, transects approximately 1000 feet

apart were conducted perpendicular to the main

axis of the Florida Keys. The Intracoastal

Waterway formed the boundary between

Everglades National Park and the Florida Keys in

this assessment. Military bases prohibited aerial

surveys of some seagrass areas.

Light Scarring

Moderate Scarring

Severe Scarring

Figure 6. Diagrammatic representation of the three categories of estimated scarring

intensity. Black space within each block represents seagrasses, and white marks represent scarring. Light scarring is defined as the presence of scars in less than 5 percent

of the delineated polygon, moderate scarring as the presence of scars in 5 to 20 percent

of the polygon, and severe scarring as the presence of scars in more than 20 percent of

the polygon.
12 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Altitudes between 300 and 500 feet provided

the best perspective for this study. Flight speeds

were between 80 and 100 knots, depending on scar

complexity and water clarity. Clear skies, calm

seas, a vertical sun angle, and clear water were

essential for conducting accurate aerial surveys.

Rain and high winds made it difficult to see scars

through the surface of the water. Glare from sunlight reflecting off the water in late afternoon and

early morning also hampered observations.

Turbidity caused by rough water during storms

usually persisted for several days. Dark-colored,

organically stained water—discharged from rivers

during and after rain storms—greatly impeded

our ability to identify scarred seagrasses during

aerial surveys.

After completing the aerial surveys, we edited and recompiled the scarring data onto a clean

set of base maps and then transferred the data into

the Marine Resources Geographic Information

System (MRGIS) at the FMRI. Complete descriptions of the MRGIS integration process, statewide

map-creation techniques, and error-correction

methodology are in Appendix A. ARC/INFO®

software (v. 6.2.1) was used in this study to analyze

scarring data and to produce output maps.

Scarring information from this study is digitally

stored and can easily be shared with other groups.

All original base maps and photograph overlays

have been archived at the FMRI.

Results

Moderately dense to dense seagrasses—i.e.,

excluding sparse and hardbottom seagrasses in the

Florida Keys and sparse Halophila beds elsewhere—total approximately 1,901,000 acres. If

hardbottom and sparse seagrasses in the Florida

Keys are included in acreage estimates, seagrasses

in Florida total nearly 2,660,000 acres (Table 2). The

distribution of seagrasses in Florida coastal waters

Severe

Moderate

Severe

Moderate

Figure 7. Recognition of scarring intensity. Contiguous small polygons of different scarring intensities

were combined into one overall intensity category. This seagrass bed would be recognized as severely

scarred overall, even though part of it is only moderately scarred.
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 13

is uneven; some counties have very little and others have a disproportionately large amount (see

figures in Appendix B). Monroe County alone contains 54.6 percent of all Florida seagrass-bed

acreage—mostly in Florida Bay and the Florida

Keys (Tables 2 and 3). Much of the remaining seagrass acreage (26.4 percent) occurs in the shallow

Gulf waters of Taylor, Citrus, Hernando, Levy, and

Dixie counties in the Big Bend region of Florida.

These counties have more seagrasses because they

have extensive, shallow-water, low-energy areas

with water quality that is generally good. These

conditions promote rapid growth and coalescence

of seagrasses. Other extensive seagrass components in deeper waters in this area are species of

Halophila, which are usually in sparse or patchy

beds. We did not include these seagrass types in

this survey.

The remaining seagrass acreage (19 percent) is

fairly evenly distributed among the other 25 counTable 1. NOAA nautical charts and USGS topographic maps used as base maps on which seagrass

scarring in Florida was represented.

Number Scale Official Name

Chart 11378 1:40,000 Intracoastal Waterway - Santa Rosa Sound to Dauphin Island

Chart 11393 1:40,000 Intracoastal Waterway - Lake Wimico to East Bay

Chart 11402 1:40,000 Intracoastal Waterway - Apalachicola to Lake Wimico

Chart 11404 1:40,000 Intracoastal Waterway - Carrabelle to Apalachicola Bay

Chart 11405 1:80,000 Apalachee Bay

Chart 11407 1:80,000 Horseshoe Point to Rock Islands

Chart 11408 1:80,000 Crystal River to Horseshoe Point

Chart 11409 1:80,000 Anclote Keys to Crystal River

Chart 11412 1:80,000 Tampa Bay and St. Joseph Sound

Chart 11413 1:40,000 Tampa Bay - northern part

Chart 11414 1:40,000 Tampa Bay - southern part

Chart 11425 1:40,000 Intracoastal Waterway - Charlotte Harbor to Tampa Bay

Chart 11427 1:40,000 Intracoastal Waterway - Fort Myers to Charlotte Harbor

Chart 11430 1:40,000 Everglades National Park - Lostmans River to Wiggins Pass

Chart 11432 1:50,000 Everglades National Park - Shark River to Lostmans River

Chart 11433 1:50,000 Everglades National Park - Whitewater Bay

Chart 11441 1:30,000 Key West Harbor and approaches

Chart 11442 1:80,000 Sombrero Key to Sand Key

Chart 11445 1:40,000 Intracoastal Waterway - Bahia Honda to Key West

Chart 11448 1:40,000 Intracoastal Waterway - Big Spanish Channel to Johnson Key

Chart 11449 1:40,000 Matecumbe to Bahia Honda Key

Chart 11451 1:80,000 Miami to Marathon and Florida Bay

Chart 11463 1:40,000 Intracoastal Waterway - Elliott Key to Matecumbe

Chart 11465 1:40,000 Intracoastal Waterway - Miami to Elliott Key

Chart 11467 1:40,000 Intracoastal Waterway - West Palm Beach to Miami

Chart 11485 1:40,000 Intracoastal Waterway - Tolomato River to Palm Shores

USGS map 1:24,000 Marquesas Keys West

USGS map 1:24,000 Marquesas Keys East

USGS map 1:24,000 Cottrell Key
14 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Table 2. Acreage of scarred seagrasses (to nearest ten acres) in each Florida coastal county in this study.

Totals in scarring categories are based on calculated values, not on rounded values. Light scarring is

defined as the presence of scars in less than 5 percent of the delineated polygon, moderate scarring as the

presence of scars in 5 to 20 percent of the polygon, and severe scarring as the presence of scars in more

than 20 percent of the polygon.

County Total Light Moderate Severe Moderate Total

Seagrass Scarring Scarring Scarring +Severe Scarring

BAY 10,530 4,050 820 80 900 4,950

BREVARD 46,190 4,160 1,940 110 2,050 6,210

BROWARD 0 (1) 0 0 0 0 0

CHARLOTTE 14,190 1,530 5,630 290 5,910 7,440

CITRUS 147,810 25,700 1,700 180 1,880 27,580

COLLIER 5,250 1,970 1,590 90 1,680 3,650

DADE 145,650* 2,740 3,970 4,500 8,480 11,220

DIXIE 111,130 2,470 1,020 0 1,020 3,490

ESCAMBIA 2,750 510 180 10 190 700

FRANKLIN 19,840 440 370 0 370 810

GULF 8,170 4,200 530 110 640 4,840

HERNANDO 146,870 7,790 710 0 710 8,500

HILLSBOROUGH 6,320 1,680 2,230 180 2,410 4,090

INDIAN RIVER 2,940 140 10 30 40 180

JEFFERSON 10,500 420 80 0 80 510

LEE 50,510 5,930 7,100 1,290 8,390 14,310

LEVY 132,400 9,970 120 0 120 10,090

MANATEE 12,160 2,480 2,200 780 2,990 5,470

MARTIN 2,310 20 10 0 10 30

MONROE 1,452,800* 14,560 10,430 5,060 15,490 30,050

OKALOOSA 3,450 310 80 0 (5) 80 390

PALM BEACH 2,510 50 20 0 20 70

PASCO 85,570 2,120 1,760 360 2,120 4,240

PINELLAS 22,920 3,800 3,870 2,010 5,880 9,680

SANTA ROSA 2,720 450 110 0 110 560

SARASOTA 4,160 720 300 30 330 1,050

ST. LUCIE 6,920 40 40 0 40 80

TAYLOR 162,860 8,100 60 0 60 8,160

VOLUSIA 8,490 1,430 1010 350 1,370 2,800

WAKULLA 29,630 2,060 730 0 730 2,790

WALTON 710 10 0 0 0 10

TOTAL 2,658,290* 109,870 48,630 15,470 64,100 173,960

* Dade County and Monroe County totals include sparse-seagrass areas and hardbottom areas that have dense patches of turtlegrass and shoal-grass intermixed. See Table 6 for a breakdown of seagrass acreage in these counties and the text for an explanation. The total area of moderately dense, dense, and contiguous seagrasses for the state is 1,900,960 acres, excluding hardbottom

and sparse seagrasses in the Florida Keys and sparse Halophila in the Big Bend region.
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 15

Table 3. Relative percentages of scarred seagrasses, by intensity level, in each Florida coastal county in

this study. Relative percentage is calculated for each category as the scarring in the county divided by scarring for the state multiplied by 100. Light scarring is defined as the presence of scars in less than 5 percent of the delineated polygon, moderate scarring as the presence of scars in 5 to 20 percent of the polygon, and severe scarring as the presence of scars in more than 20 percent of the polygon.

County Total Light Moderate Severe Moderate Total

Seagrass Scarring Scarring Scarring +Severe Scarring

BAY 0.4 3.7 1.7 0.5 1.4 2.8

BREVARD 1.7 3.8 4.0 0.7 3.2 3.6

BROWARD 0.0 0.0 0.0 0.0 0.0 0.0

CHARLOTTE 0.5 1.4 11.6 1.9 9.2 4.3

CITRUS 5.6 23.4 3.5 1.1 2.9 15.8

COLLIER 0.2 1.8 3.3 0.6 2.6 2.1

DADE 5.5 2.5 8.2 29.1 13.2 6.4

DIXIE 4.2 2.2 2.1 0.0 1.6 2.0

ESCAMBIA 0.1 0.5 0.4 0.1 0.3 0.4

FRANKLIN 0.8 0.4 0.8 0.0 0.6 0.5

GULF 0.3 3.8 1.1 0.7 1.0 2.8

HERNANDO 5.5 7.1 1.5 0.0 1.1 4.9

HILLSBOROUGH 0.2 1.5 4.6 1.2 3.8 2.4

INDIAN RIVER 0.1 0.1 0.0 0.2 0.1 0.1

JEFFERSON 0.4 0.4 0.2 0.0 0.1 0.3

LEE 1.9 5.4 14.6 8.3 13.1 8.2

LEVY 5.0 9.1 0.2 0.0 0.2 5.8

MANATEE 0.5 2.3 4.5 5.1 4.7 3.1

MARTIN 0.1 0.0 0.0 0.0 0.0 0.0

MONROE 54.6 13.2 21.4 32.7 24.2 17.3

OKALOOSA 0.1 0.3 0.2 0.0 0.1 0.2

PALM BEACH 0.1 0.0 0.0 0.0 0.0 0.0

PASCO 3.2 1.9 3.6 2.3 3.3 2.4

PINELLAS 0.9 3.5 8.0 13.0 9.2 5.6

SANTA ROSA 0.1 0.4 0.2 0.0 0.2 0.3

SARASOTA 0.2 0.6 0.6 0.2 0.5 0.6

ST. LUCIE 0.3 0.0 0.1 0.0 0.1 0.0

TAYLOR 6.1 7.4 0.1 0.0 0.1 4.7

VOLUSIA 0.3 1.3 2.1 2.3 2.1 1.6

WAKULLA 1.1 1.9 1.5 0.0 1.1 1.6

WALTON 0.0 0.0 0.0 0.0 0.0 0.0
16 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

ties, mostly in embayments and lagoonal systems.

Twenty-two counties have less than 50,000 acres of

seagrass, and the majority of those have less than

20,000 acres. The median seagrass acreage for the

31 coastal counties in this study is approximately

10,500 acres. After Monroe County (1,452,800

acres), Taylor county has the largest seagrass

acreage (162,860 acres). Of the Florida counties

that contain at least some seagrass, Broward

County had the smallest acreage; approximately

one acre of seagrass could be recognized from seagrass-distribution sources.

The least amount of total scarring (the sum of

the light, moderate, and severe categories) occurred

in those counties that have little seagrass acreage

(e.g., Broward, Indian River, and Walton). For scarring to be extensive, the first requirement is that a

county must contain a substantial acreage of seagrass. Counties with little seagrass acreage, but

with all of it scarred, would rank high in statewide

scarring (Table 4). Therefore, ranking counties

based on the percentage of seagrass scarred within

the county can be deceptive.

For comparative purposes, then, counties

must be ranked based on their percentages of scarring relative to scarring for the entire state.

Relative to the whole state, the greatest amount of

total scarring occurred, as would be expected from

seagrass distributions, in Monroe and Citrus counties (Tables 2, 3, and 5). Lee, Dade, Levy, and

Pinellas counties also had substantial scarring. Of

greatest immediate concern is scarring in the moderate and severe categories (M/S scarring). Scarring

in the light category in most areas is probably not

of immediate concern in protecting seagrasses,

unless the area is subject to increasing boat use.

The counties with the most M/S scarring were

Monroe, Dade, Lee, Charlotte, and Pinellas. Most

scarring in Citrus and Levy counties was in the

light category, so these two counties are of lower

importance when only M/S scarring is considered.

Fourteen counties each had less than one percent

of the state’s M/S scarring. Of these, Walton,

Broward, Martin, Palm Beach, St. Lucie, and

Indian River counties had the lowest amounts of

M/S scarring because they all have low seagrass

acreage. Of the counties containing substantial

acreages of seagrass (i.e., those with more than one

percent of statewide coverage), Taylor, Hernando,

Wakulla, Dixie, and Citrus counties had the least

M/S-scarring acreage. These counties are all in the

Big Bend region of Florida, which is sparsely populated and has low numbers of registered boats.

These five counties account for 22.5 percent of the

state’s seagrass acreage. Scarring extents and

intensities for all 31 coastal counties in this study

are illustrated in the figures in Appendix B.

Generalized seagrass distributions compiled

from various sources may be misleading if data

were based on different definitions for sparse seagrass or included patchy (but dense) seagrasses

within a polygon. In this study, sparse and hardbottom seagrasses in Monroe and Dade counties

were included in the overall seagrass distributions

because substantial patches of dense and moderately dense shoal-grass and turtle-grass were intermixed and could not be separately delineated. In

areas of the Big Bend and Indian River Lagoon,

however, we deleted sparse-seagrass categories

from mapping and analysis because they were

mostly very sparse Halophila beds, which are usually in deeper waters and which may not be pertinent to ecological concerns addressed in this study.

Nevertheless, we separated the seagrass distributions for Monroe and Dade counties into

sparse/hardbottom and dense/moderately dense

seagrass acreages (Table 6) for those who wish to

eliminate these categories from scarring-extent calculations. All of our calculations were based on the

total seagrass acreages for Monroe and Dade counties.

Polygons representing scarring in areas

where sparse seagrasses had been excluded from

the generalized distribution were retained in the

analysis because they indicated the presence of

seagrasses, as confirmed in the aerial surveys.

Caution must be used when assessing the meaning

of the data presented in this study. Although we

have attempted to reduce distribution errors, inaccuracies remain because of the broad nature of

this type of study. Mapping of seagrasses and scarring will be in constant flux as more detailed data

are generated for different areas.

To more broadly identify differences in seagrass-scarring distribution, five regions (Figure 8)
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 17

Table 4. Percentages of scarred seagrasses, by intensity level, within each Florida coastal county in this

study. Light scarring is defined as the presence of scars in less than 5 percent of the delineated polygon,

moderate scarring as the presence of scars in 5 to 20 percent of the polygon, and severe scarring as the

presence of scars in more than 20 percent of the polygon. The percentage of scarred seagrasses for the entire

state in each category is light = 4.1%, moderate = 1.8%, severe = 0.6%, moderate + severe = 2.4%,

and total scarring = 6.5%.

Total Percent Percent Percent Percent Percent

County Seagrass Light Moderate Severe Moderate Total

Acres Scarring Scarring Scarring +Severe Scarring

BAY 10,530 38.4 7.8 0.7 8.5 47.0

BREVARD 46,190 9.0 4.2 0.2 4.4 13.4

BROWARD 1 100.0 0.0 0.0 0.0 100.0

CHARLOTTE 14,190 10.8 39.6 2.0 41.6 52.4

CITRUS 147,810 17.4 1.2 0.1 1.3 18.7

COLLIER 5,250 37.5 30.3 1.7 32.0 69.5

DADE 145,650 1.9 2.7 3.1 5.8 7.7

DIXIE 111,130 2.2 0.9 0.0 0.9 3.1

ESCAMBIA 2,750 18.7 6.4 0.3 6.7 25.4

FRANKLIN 19,840 2.2 1.9 0.0 1.9 4.1

GULF 8,170 51.4 6.6 1.3 7.9 59.3

HERNANDO 146,870 5.3 0.5 0.0 0.5 5.8

HILLSBOROUGH 6,320 26.6 35.3 2.9 38.2 64.8

INDIAN RIVER 2,940 4.8 0.3 1.1 1.4 6.2

JEFFERSON 10,500 4.0 0.8 0.0 0.8 4.8

LEE 50,510 11.7 14.1 2.6 16.7 28.4

LEVY 132,400 7.5 0.1 0.0 0.1 7.6

MANATEE 12,160 20.4 18.1 6.5 24.6 45.0

MARTIN 2,310 1.0 0.4 0.0 0.4 1.4

MONROE 1,452,800 1.0 0.7 0.4 1.1 2.1

OKALOOSA 3,450 9.0 2.2 0.1 2.3 11.3

PALM BEACH 2,510 2.1 0.9 0.0 0.9 3.0

PASCO 85,570 2.5 2.1 0.4 2.5 5.0

PINELLAS 22,920 16.6 16.9 8.8 25.7 42.3

SANTA ROSA 2,720 16.4 4.1 0.0 4.1 20.5

SARASOTA 4,160 17.2 7.2 0.8 8.0 26.0

ST. LUCIE 6,920 0.6 0.6 0.0 0.6 1.2

TAYLOR 162,860 5.0 0.0 0.0 0.0 5.0

VOLUSIA 8,490 16.9 11.9 4.2 16.1 33.0

WAKULLA 29,630 6.9 2.5 0.0 2.5 9.4

WALTON 710 1.6 0.0 0.0 0.0 1.6
18 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Table 5. County rankings of scarred-seagrass acreage, by scarring intensity, in each Florida coastal county in this study. Rank is in decreasing order of acreage scarred. Counties with the same acreage are ranked

alphabetically. Light scarring is defined as the presence of scars in less than 5 percent of the delineated

polygon, moderate scarring as the presence of scars in 5 to 20 percent of the polygon, and severe scarring as the presence of scars in more than 20 percent of the polygon.

Total Light Moderate Severe Moderate Total

Seagrass Scarring Scarring Scarring +Severe Scarring

1 MONROE CITRUS MONROE MONROE MONROE MONROE

2 TAYLOR MONROE LEE DADE DADE CITRUS

3 CITRUS LEVY CHARLOTTE PINELLAS LEE LEE

4 HERNANDO TAYLOR DADE LEE CHARLOTTE DADE

5 DADE HERNANDO PINELLAS MANATEE PINELLAS LEVY

6 LEVY LEE HILLSBOROUGH PASCO MANATEE PINELLAS

7 DIXIE GULF MANATEE VOLUSIA HILLSBOROUGH HERNANDO

8 PASCO BREVARD BREVARD CHARLOTTE PASCO TAYLOR

9 LEE BAY PASCO CITRUS BREVARD CHARLOTTE

10 BREVARD PINELLAS CITRUS HILLSBOROUGH CITRUS BREVARD

11 WAKULLA DADE COLLIER BREVARD* COLLIER MANATEE

12 PINELLAS* MANATEE DIXIE GULF* VOLUSIA BAY

13 FRANKLIN* DIXIE VOLUSIA COLLIER* DIXIE GULF

14 CHARLOTTE* PASCO BAY BAY* BAY PASCO

15 MANATEE* WAKULLA WAKULLA INDIAN RIVER* WAKULLA HILLSBOROUGH

16 BAY* COLLIER HERNANDO SARASOTA* HERNANDO COLLIER

17 JEFFERSON* HILLSBOROUGH GULF ESCAMBIA* GULF DIXIE

18 GULF* CHARLOTTE FRANKLIN* BROWARD* FRANKLIN* VOLUSIA

19 VOLUSIA* VOLUSIA SARASOTA* DIXIE* SARASOTA* WAKULLA

20 ST. LUCIE* SARASOTA* ESCAMBIA* FRANKLIN* ESCAMBIA* SARASOTA*

21 HILLSBOROUGH* ESCAMBIA* LEVY* HERNANDO* LEVY* FRANKLIN*

22 COLLIER* SANTA ROSA* SANTA ROSA* JEFFERSON* SANTA ROSA* ESCAMBIA*

23 SARASOTA* FRANKLIN* JEFFERSON* LEVY* JEFFERSON* SANTA ROSA*

24 OKALOOSA* JEFFERSON* OKALOOSA* MARTIN* OKALOOSA* JEFFERSON*

25 INDIAN RIVER* OKALOOSA* TAYLOR* OKALOOSA* TAYLOR* OKALOOSA*

26 ESCAMBIA* INDIAN RIVER* ST. LUCIE* PALM BEACH* INDIAN RIVER* INDIAN RIVER*

27 SANTA ROSA* PALM BEACH* PALM BEACH* SANTA ROSA* ST. LUCIE* ST. LUCIE*

28 PALM BEACH* ST. LUCIE* INDIAN RIVER* ST. LUCIE* PALM BEACH* PALM BEACH*

29 MARTIN* MARTIN* MARTIN* TAYLOR* MARTIN* MARTIN*

30 WALTON* WALTON* BROWARD* WAKULLA* BROWARD* WALTON*

31 BROWARD* BROWARD* WALTON* WALTON* WALTON* BROWARD*

* Relative percentage is less than one percent.
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 19

were demarcated in the analysis of scarring extents

and intensities: Region 1. Panhandle (Escambia

County–Franklin County), Region 2. Big Bend

(Wakulla County–Pasco County), Region 3. Gulf

Peninsula (Pinellas County–Lee County), Region 4.

Atlantic Peninsula (Palm Beach County–Volusia

County), and Region 5. South Florida (Collier

County–Broward County). Acreages of scarred

seagrasses occurring in these regions are in Table 7.

The areas of Florida with the greatest

acreages of M/S scarring were the Gulf Peninsula

and South Florida regions. Based only on the

severe-scarring category, however, the South

Florida region had twice the scarred acreage of the

Gulf Peninsula region. If the light-scarring category is included, the Big Bend region had the greatest total of scarred-seagrass acreage. However, the

light-scarring category may not be of greatest concern in protecting seagrasses from scarring; therefore, the Big Bend region may not be a priority for

a management program, except for protecting sites

where M/S scarring occurs and ensuring that scarring does not become worse.

When M/S scarring is viewed relative to the

total seagrass acreage in the region, the most

threatened region is the Gulf Peninsula (23.5 percent of its seagrasses scarred); it has extensive scarring relative to the moderate acreage of seagrasses

there. Because of the extensive acreages of seagrasses in the South Florida and Big Bend regions,

scarring levels (1.6 percent and 0.8 percent of their

seagrasses scarred) were low relative to the area of

total seagrasses present. However, most of these

seagrasses occur in water depths where they are

unlikely to be scarred.

Region 1. Panhandle: This region has the least

acreage of seagrass in the state (Table 7). Bay and

Table 6. Acreages (to nearest ten acres) of seagrass-density categories in the Florida Keys.

County Total Seagrass Moderate/Dense Sparse/Hardbottom

Seagrass Seagrass

DADE 145,650 120,680 24,320

MONROE 1,452,800 717,440 733,210

TOTAL 1,598,450 838,120 757,530

Table 7. Acreages of scarred seagrasses (to nearest ten acres) in each region of Florida demarcated in this

study. Light scarring is defined as the presence of scars in less than 5 percent of the delineated polygon,

moderate scarring as the presence of scars in 5 to 20 percent of the polygon, and severe scarring as the

presence of scars in more than 20 percent of the polygon.

Total Light Moderate Severe Moderate Total Region Seagrass Scarring Scarring Scarring +Severe Scarring

1. PANHANDLE 48,170 9,970 2,090 200 2,290 12,260

2. BIG BEND 826,770 58,630 6,180 540 6,720 65,350

3. GULF PENINSULA 110,260 16,140 21,330 4,580 25,910 42,050

4. ATLANTIC PENINSULA 69,360 250 3,030 490 3,520 3,770

5. SOUTH FLORIDA 1,603,700* 19,270 15,990 9,650 25,640 44,910

* South Florida total includes sparse-seagrass areas and hardbottom areas with moderately dense and dense patches of turtlegrass and shoal-grass intermixed. See Table 6 for a breakdown of seagrass acreage in these counties and the text for an explanation. The total area of moderately dense, dense, and contiguous seagrasses in the state is 1,900,960 acres, excluding hardbottom and sparse seagrasses in the Florida Keys and sparse Halophila beds in the Big Bend region.
Okaloosa

Gulf

Dixie

Levy

Volusia Citrus

Brevard

Pasco

Pinellas

St. Lucie

Martin

Palm Beach

Collier Broward

Dade

Escambia

Santa Rosa

Walton

Jefferson Bay

Wakulla

Taylor

Franklin

Hernando

Hillsborough

Manatee

Charlotte

Lee

Indian River

Sarasota

Monroe

Alabama Georgia

Gulf

of

Mexico

Atlantic

Ocean

E

N

W

S

Region 1. Panhandle

Region 2. Big Bend

Region 3. Gulf Peninsula

Region 4. Atlantic Peninsula

Region 5. South Florida

20 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Figure 8. Regions of Florida analyzed for scarred seagrasses.
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 21

Gulf counties had the greatest acreages of both

total and M/S scarring in this region. Scarring in

this region was principally in the light category,

although some of the small amount of seagrass in

the more developed embayments had severe scarring. St. Joseph Bay, East Bay, and St. Andrew Bay,

along with The Narrows and Santa Rosa Sound,

were the principal foci for scarring. Big Lagoon in

Escambia County had extensive light and moderate

scarring, as did areas adjacent to Perdido Bay and

Perdido Island.

Region 2. Big Bend: The Big Bend region contains extensive areas of very shallow water and

intricate shorelines. Even so, not much scarring

was observed (Table 7). Within this region, Citrus

County had the most extensive acreage of total

scarring, and Pasco County had the most M/S

scarring. Levy, Taylor, and Hernando counties

also had a substantial amount of total scarring,

most of which was in the light category. The extent

of scarring was unexpected because of these counties’ lower population densities. However, the

large amount of light scarring may have partially

been an artifact of the small-scale maps that prevented detailed polygon delineation in this

region.

Region 3. Gulf Peninsula: The total acreage of

scarred seagrasses was extensive in this region

(Table 7). M/S scarring totaled 25,910 acres, which

was the most in the state. Lee County had the

most extensive total and M/S scarring of the

counties in this region. The seagrass flats of Estero

Bay, Pine Island Sound, and Matlacha Pass (all in

Lee County) were criss-crossed with M/S scarring. Figure 9 illustrates detailed scarring patterns

around Pine Island in Charlotte County. Note the

scarred area to the southwest of the marina (lower

left). Even though a marked boat channel (narrow

band of light blue) extends west from the marina

to open water and the Intracoastal Waterway,

boats leaving the marina often take a shortcut

south and as a result scar shallow seagrass beds.

From Sarasota County to Pinellas County,

light and moderate scarring were common. Pinellas

County had the largest acreage of total and M/S

scarring in the Tampa Bay region. The Gulf

Peninsula region contains two extensive bay systems: Tampa Bay, which is highly developed, and

Charlotte Harbor, which is much less developed.

A comparison of the two bay systems shows that

both total and M/S scarring were approximately

the same for the two embayments. Charlotte

Harbor has approximately 23,000 more acres of

seagrass than Tampa Bay does, so scarring may

have been more critical in Tampa Bay relative to

its total seagrass acreage.

Region 4. Atlantic Peninsula: This region had

the lowest total acreage of scarred seagrasses

(Table 7). Most scarring occurred in the northern

part of Brevard County and the southern part of

Volusia County, so the northern part of this region

had the most extensive scarring. Within this

region, Brevard County had the most total and

M/S scarring, although Volusia County also had

substantial M/S scarring. Relative to the total

acreage of seagrass in the county, the scarring in

Volusia County may be more deleterious.

Counties south of Brevard County did not have

substantial acreages of seagrass; therefore, scarring there was not extensive.

Region 5. South Florida: This region has the

largest acreage of seagrass in the state—most of it

in Monroe County (Table 7). This region also had

the greatest acreage of severe scarring in the state.

Monroe County had by far the most scarring in all

categories in this region. Of the other counties in

this region, Dade County had substantial scarring

in the total and M/S categories, principally in

southern Biscayne Bay.

For this region, a better understanding of

scarring can be obtained by viewing the Florida

Keys as a single entity that crosses county boundaries. If the extensive area of seagrasses in Florida

Bay is excluded from the scarring analysis, the

Florida Keys contains what are probably the most

egregious examples of scarring in the state. This

area, which is in Dade and Monroe counties, provided a greater diversity of scarring types than

any other county in the state and was surveyed in

greater detail to provide an example of how to

examine site-specific types of scarring (Kruer

1994).

Virtually all seagrass banks and flats in the

Florida Keys have some scarring, and scar density

is generally greatest near developed islands and

in areas of more intensive boating activity

(Matthews et al. 1991). Scarred seagrasses were

observed from the high intertidal zone to a depth

of approximately six feet at low tide. The scars in

deeper water were near ports at Key West and

Stock Island; northeast of Big Pine Key, where

commercial fish-trap boats take shortcuts through
22 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Pineland

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

1 .5 0 1

KILOMETERS

1 .5 0 1

MILES

SCALE 1:24,000 Scale 1:40,000

Water

Land

“Nonscarred” Seagrass

Light Scarring

Moderate Scarring

Severe Scarring

Marina

Pine Island

Part Island

Figure 9. Detailed map of scarred seagrasses—Pine Island, Lee County.
Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

Light Scarring

Moderate Scarring

Severe Scarring

Windley Key

1 .5 0 1

KILOMETERS

1 .5 0 1

MILES

SCALE 1:24,000 SCALE 1:40,000

F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 23

Figure 10. Detailed map of scarred seagrasses—Windley Key, Monroe County.
24 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

shallow channels; near Marathon and Islamorada,

where large vessels dock; and in and along the

Intracoastal Waterway on the Florida Bay side of

the upper Florida Keys.

Approximately 900 scarred areas were identified in the Florida Keys. Light scarring totaled

14,650 acres, moderate scarring totaled 10,400 acres,

and severe scarring totaled 5,020 acres. The greatest concentration of M/S scarring was observed in

the upper Keys. Scarring intensity ranged from a

few scars at some sites to numerous propeller and

grounding scars at others. Some formerly vegetated areas were covered by displaced sediment

from extensively scarred and destabilized seagrass beds nearby. Moderately and severely

scarred sites in the lower Florida Keys from the

Marquesas Keys to near Snipe Key, for which

additional information was collected, are listed in

Tables 8 and 9 (Kruer 1994). These sites were evaluated for probable causes of scarring based on

observed boating activity, environmental characteristics of the area, personal knowledge, and discussions with many boaters.

A notable example of the intensity of scarring

that occurs in some parts of Florida is around

Windley Key, in the upper Florida Keys. Windley

Key is in the Florida Keys National Marine

Sanctuary, and its waters are designated as Class

III Outstanding Florida Waters. It includes a variety of shallow marine communities and is a transitional area between high-energy oceanic waters

and the more protected waters of Florida Bay and

Everglades National Park. Whale Harbor and

Snake Creek channels, both with relatively deep

water, connect the extensive, shallow seagrass

flats of Florida Bay with deeper oceanic waters.

Endangered West Indian manatees, American

crocodiles, and seaturtles are known to inhabit

these waters. The area is also surrounded by coral

reefs and hardbottom communities that attract

many tourists and fishermen.

As a result of intense boating activity and

lack of proper protection, the Windley Key area

contains some of the most heavily scarred seagrass flats in south Florida. Figure 10 illustrates

the extent of seagrass scarring around Windley

Key. Kruer (1994) noted the loss of seagrasses

along channel edges and that eroded sediments

were being deposited on seagrasses. Unmarked

channels had been cut through shallow-water seagrass flats and between mangroves. Boat wakes

severely eroded seagrass beds along the offshore

channel edges. Boating activity originated from

facilities located at Whale Harbor Channel and at

Snake Creek and from the more than 31,000 linear

feet of bulkhead docks along canals in a residential subdivision.

Scarring of seagrasses in the Florida Keys has

occurred for some time—probably since combustion engines (outboard and inboard) were installed in boats. However, the problem of seagrass

scarring has become acute because of the increasing residential population; the increasing

popularity of boating, fishing, diving, and other

water sports; and increasing tourism. New propdredged channels continue to appear, some thousands of feet long, providing access for larger and

more numerous vessels into areas not previously

accessible. Many shallow flats and banks are now

severely eroded due to constant scarrings, ship

groundings, chronic wave action, and water-current scouring (Kruer 1994).

Discussion

The majority of Florida’s moderate/severe (M/S)

seagrass scarring (68.9 percent) occurred in five

counties: Monroe, Dade, Lee, Charlotte, and

Pinellas. These same counties contain 63.4 percent

of the state’s seagrass acreage. However, if

Monroe County is excluded from analysis—because of its disproportionately large amount of

seagrass acreage and scarring—the five counties

that have the most M/S scarring contain only 9.3

percent of the state’s seagrass acreage but 49.4

percent of its M/S scarring. What could be the

cause of so much scarring in these counties? One

important correlation exists with population density, as reflected in vessel registrations for each of

the counties. For example, M/S scarring of seagrass beds is greater in the densely populated

Gulf Peninsula region than it is in the sparsely

populated Big Bend region.

Florida’s population nearly doubled between

1970 and 1990: from 6,791,000 to 12,938,000.

During the same period, the number of vessel

registrations (recreational and commercial) more
Table 8. Moderately scarred sites—Marquesas Keys to Snipe Key (1992–93). Adapted from Kruer (1994).

Site # Adjacent Key Probable Suggested Comments Cause1 Management2

13 Marquesas Keys A, S ED Shallow channel between islands with popular beaches

15 Marquesas Keys A, S ED Shallow channel between two islands

32 Marquesas Keys I, S ED Entrance to natural channel

46 Boca Grande Key C, S C At entrance to main channel, existing markers (#17 and #18) on

chart, marker 18 in shallow zone, vessels pass on shallow side.

50 Boca Grande Key C, S C Markers # 13 and 14 not located as shown on chart 11441

75 Archer Key C, S C, EN Adjacent to single marker # 8 shown on chart 11441, oversized

vessels, needs gated markers.

105 Mule Key C, S C, EN Confined area between markers, used by oversized vessels

113 Mule Key C, S ED Area of concentrated traffic near channel markers

121 Key West S ED Isolated bank (Middle Grounds) in center of Northwest Channel

123 Wisteria Island C, L, S C, ED, EN Heavily traveled anchorage on west edge of Key West Channel

127 Fleming Key C, S C, ED Inadequately marked channel through large bank

142 Fleming Key S ED, EN On inside of several markers

145 Fleming Key S C, ED On edge of main channel near marker

150 Key West P, S C, ED, EN Outside of markers in access to Garrison Bight

151 Key West C, P, S C, ED Inside Garrison Bight, outside of partly marked dredged 

channel

152 Key West C, P, S C, ED Inside Garrison Bight, outside of partly marked dredged 

channel

155 Sigsbee Park S C, ED At end of dredged area

156 Key West A, S C, ED Boats accessing dredged channel

157 Key West C, P, S C, ED, EN Cow Key Channel, part marked, part unmarked, high-speed

traffic

163 Stock Island P, S C, ED, EN Adjacent to Safe Harbor Channel

165 Stock Island L, P, S C, ED, EN Anchorage east of Stock Island in Boca Chica Channel

166 Stock Island L, P ED, EN Anchorage east of Stock Island in Boca Chica Channel and near

ramp

174 Boca Chica S ED, EN At entrance to dredged part of Boca Chica Channel

181 Bay Keys I, S ED, EN Commercial tour boats and recreational boats accessing 

Bay Keys from the south 201 Lower Harbor

Keys I, S ED, EN Long, illegally marked channel

204 Channel Key I, S ED Part of old Backcountry Waterway

207 Channel Key I, S C, ED Cut through bank between islands

223 Fish Hawk Key I, S C, ED Cut through long linear bank

232 Geiger Key A, I, S ED, EN Shallow channel leaving residential canal

236 Saddlebunch Key C,S C, ED On bank near marked channel

238 Big Coppitt Key A,C ED, EN Marked access to canal trailer park

245 Halfmoon Key A, I, S ED, EN Access to shallow embayment

251 Mud Keys S C, ED Channel leaving Waltz Key Basin

1 Probable Cause: A = access point, C = poor channel markers, I = illegal aids to navigation, L = live-aboards, P = proximity, 

S = shortcut.

2 Suggested Management: C = new or improved markers, ED = education, EN = better enforcement, R = restricted area.

F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 25
26 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Table 9. Severely scarred sites—Marquesas Keys to Snipe Key (1992–1993). Adapted from Kruer (1994).

Site # Adjacent Key Probable Suggested Comments Cause1 Management2

7 Marquesas Keys S ED, EN From large vessel in early 1980s, now enlarged

129 Wisteria Island C, L, S C, ED, EN Heavily traveled anchorage on east side of Key West

Channel

138 Fleming Key I, S C, ED At shallow end of a natural channel

158 Stock Island A ED, EN Boats accessing residential area in shallow water

160 Key West A, L ED, EN Cow Key Channel live-aboard anchorage and Cow Key

Channel south of bridge

170 Stock Island S C, ED, EN Large vessels shortcutting into Boca Chica Channel

231 Geiger Key A, I, P, S C, ED, EN Access to Geiger Key Marina and area

1 Probable Cause: A = access point, C = poor channel markers, I = illegal aids to navigation, L = live-aboards, P = proximity, 

S = shortcut.

2 Suggested Management: C = new or improved markers, ED = education, EN = better enforcement, R = restricted area.

than tripled: from 235,000 to 716,000. Clearly, not

only is the population increasing, but the percentage of the population that owns boats is also

increasing. Substantial increases in both population and number of vessels suggest that our state’s

water resources are being used at an increasing

rate, and therefore its seagrasses are in increasing

danger of being damaged.

By 1992–93, total power-boat registration for

the 31 counties in this survey had reached 493,406

vessels (Bureau of Vessel Titles and Registrations

1994). The greatest percentage of boats in most

coastal counties were registered as pleasure boats

(Table 10). For the 31 counties in this study, only

6.4 percent of vessels were registered as commercial craft. The five counties with the greatest number of vessel registrations were Dade, Pinellas,

Broward, Hillsborough, and Lee. These five counties contained 40.6 percent of all vessels registered

in the 31 coastal counties in this study. The number of registered vessels in the five counties with

the greatest acreage of M/S scarring was 156,899

in 1992–93, which is 14 times greater than that of

the registered vessels in the five counties that had

the least M/S scarring (11,031 acres) and that also

had substantial seagrass acreage. In four of the

five counties with the most registered craft, M/S

scarring of seagrasses was also extensive (25,160

acres or 39 percent). In Broward County, scarring

levels were low because it had only slightly more

than one acre of seagrasses (based on small-scale

photography).

The number of vessels registered in a county

is not always a predictor of seagrass scarring in

that county. Many counties with large numbers of

registered watercraft lack substantial seagrass

acreage. For example, Palm Beach County has

30,929 and Broward County has 42,612 registered

vessels (Table 10), but each has less than 20 acres

of M/S scarring (Table 2). In contrast, Monroe

County has a moderate number of vessels registered (20,163) but contains the greatest acreage of

M/S scarring in the state.

Whether a vessel is used for commercial or

recreational purposes may influence where it is

predominantly used. Commercial vessels are usually larger, work farther offshore, and are limited

to a few ports with deeper access; smaller vessels

can be trailered to attractive inshore fishing and

watersports areas such as the Florida Keys and

Charlotte Harbor. Pleasure boats (excluding sailboats) in most counties compose more than 90

percent of registered vessels (Table 10). In Monroe

County, by contrast, only 80 percent (16,152) of the

vessels are registered as pleasure boats; the

remainder are registered as commercial vessels.

Pleasure-boat registrations indicate where trailering may likely originate. Therefore, seagrass scarring in the Florida Keys may be caused in part by

smaller boats trailered in from Palm Beach, Dade,

and Broward counties and elsewhere. Nevertheless, seagrass scarring is not limited to a single

group of boaters; all user-groups scar seagrasses

to some degree.
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 27

Table 10. Vessel registrations in 1992–1993 in the 31 Florida coastal counties in this study. Table does

not include sailboat registrations.

County Pleasure Percentage Commercial Total County

Craft Pleasure and Dealer

Craft Craft Watercraft Rank

BAY 13,212 89.9 1,488 14,700 15

BREVARD 25,763 93.8 1,716 27,479 7

BROWARD 39,930 93.7 2,682 42,612 3

CHARLOTTE 14,004 93.7 947 14,951 14

CITRUS 11,445 91.7 1,039 12,484 19

COLLIER 13,791 92.2 1,171 14,962 13

DADE 44,542 95.2 2,231 46,773 1

DIXIE 1,544 77.0 461 2,005 30

ESCAMBIA 15,297 96.6 537 15,834 11

FRANKLIN 1,424 57.7 1,045 2,469 27

GULF 1,866 86.8 284 2,150 29

HERNANDO 5,293 96.1 212 5,505 23

HILLSBOROUGH 35,126 97.3 973 36,099 4

INDIAN RIVER 7,796 94.1 492 8,288 21

JEFFERSON 669 96.3 26 695 31

LEE 29,409 93.6 2,007 31,416 5

LEVY 2,162 86.1 348 2,510 26

MANATEE 12,865 94.5 752 13,617 17

MARTIN 12,041 94.0 767 12,808 18

MONROE 16,152 80.1 4,011 20,163 8

OKALOOSA 13,059 94.3 795 13,854 16

PALM BEACH 29,862 96.6 1,067 30,929 6

PASCO 14,800 96.6 528 15,328 12

PINELLAS 41,317 94.8 2,279 43,596 2

SANTA ROSA 7,377 95.4 359 7,736 22

SARASOTA 16,272 95.0 848 17,120 10

ST. LUCIE 8,839 94.2 543 9,382 20

TAYLOR 2,399 91.0 237 2,636 25

VOLUSIA 18,286 95.4 876 19,162 9

WAKULLA 3,221 86.4 509 3,730 24

WALTON 2,308 95.6 105 2,413 28
28 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Table 11. Vessel registrations in 1992–93 (Bureau of Vessel Titles and Registrations 1994) in the five

regions of Florida demarcated in this survey (see Figure 8). Table does not include sailboat registrations.

Region Total Pleasure % Pleasure Regional Rank

Watercraft Craft (PC) Craft PC %PC

1. PANHANDLE 59,156 54,525 92.2 4 4

2. BIG BEND 44,893 41,533 92.5 5 3

3. GULF PENINSULA 156,799 148,993 95.0 1 1

4. ATLANTIC PENINSULA 108,048 102,587 94.9 3 2

5. SOUTH FLORIDA 124,510 114,415 91.9 2 5

TOTAL 493,406 462,053 93.6 — —

On a regional basis, vessel registrations were

greatest in the Gulf Peninsula region (Table 11).

Vessel registrations in the Panhandle and Big Bend

regions were insignificant compared to those in the

other three regions. The Gulf Peninsula region not

only had the greatest number of registered vessels,

it also had the greatest percentage registered as

pleasure craft (95 percent) and the most M/S scarring. The South Florida region was second in the

number of registered vessels and nearly equal to

the Gulf Peninsula region in M/S scarring. The

Gulf Peninsula and South Florida regions contained 57 percent of all registered vessels in the 31

coastal counties in this study. The lowest number

of registered vessels was in the Big Bend region

(9.1 percent).

Many authors have speculated on the situations in which seagrasses are scarred (e.g.,

Woodburn et al. 1957, Godcharles 1971, Eleuterius

1987, Zieman and Zieman 1989, Wilderness

Society et al. 1990). Our discussions with boaters,

as well as our personal experiences, suggest that

scarring of seagrasses could result when one or

more of the following situations occur: 

• when boaters misjudge water depth and accidentally scar seagrass beds; 

• when boaters who lack navigational charts or

the skill to use them stray from poorly

marked channels and accidentally scar seagrass beds; 

• when boaters intentionally leave marked

channels to take shortcuts through shallow

seagrass beds, knowing that seagrasses may

be scarred;

• when boaters carelessly navigate in shallow

seagrass beds because they believe scars heal

quickly; 

• when inexperienced boaters engage in recreational and commercial fishing in shallow

seagrass flats, thinking that their boat’s designed draft is not deep enough to scar seagrasses or that the design will prevent damage to their boat;

• when boaters overload their vessels, causing

deeper drafts than the boaters realize;

• when boaters anchor over shallow seagrass

beds, where their boats swing at anchor and

scar seagrasses; 

• when boaters intentionally prop-dredge to

create a channel; and

• when inexperienced boaters, ignorant of

what seagrasses are and the benefits they provide, accept as the behavioral norm local

boating customs that disregard the environment.

The situations that promote scarring can be

grouped into two general categories: (1) All too

often, boaters accidentally or intentionally pass

through water that is too shallow for the draft of

their vessels. The average size, draft, and power of

vessels are increasing; therefore, bigger, more powerful vessels are being navigated through shallow

waters and are scarring more seagrass acreage.

Also, water sports often occur in shallow water,

although suitable deeper water may be found

nearby. Boaters use flats boats, which are designed

to operate in shallow water, to gain access to more

remote, shallow seagrass beds. However, inexperi-
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 29

enced users of flats boats, ignorant of the proper

use of such boats and the great value of seagrasses, may extensively scar shallow seagrass beds in

areas near marinas and launching ramps.

Inexperienced boaters, unfamiliar with the

location of channels and often lacking navigational charts, travel through areas where official channel markers are infrequent or poorly located. Some

channel markers are not located as shown on

charts, and many are immediately adjacent to shallow-water seagrasses. Furthermore, many boaters

are unfamiliar with the meanings of U.S. Coast

Guard Aids to Navigation; hence, a single marker

may confuse an inexperienced boater who is

unable to read either the marker or water depth.

Running aground is more likely if a boater passes

on the wrong side of a marker located on the edge

of a seagrass flat. Markers in some channels do not

extend an adequate distance beyond the ends of

channels to discourage boaters from crossing the

edges of seagrass beds. Notably, many M/Sscarred seagrasses are in or adjacent to the ends of

officially marked channels.

Illegal aids to navigation (e.g., PVC, wood, or

metal posts and marker buoys) are widespread,

especially in the Florida Keys. Only those who

place these markers know what is intended. Often

these illegal markers indicate where prop-dredging has deepened shallow areas so small boats can

get between deeper areas. Boaters in larger vessels

may attempt to use such markers and unexpectedly pass through water too shallow for their boats.

(2) Coastal property is popular because it

allows direct access to the water. Extensive shoreline development in shallow bays and adjacent to

shallow seagrass flats results in increased scarring.

Some seagrass scarring is caused by boaters who

attempt to gain access to shoreline development

and by coastal landowners—and their families and

friends—boating in nearby shallows. Many

dredged canals leading from residential areas terminate in relatively shallow water (Figure 11).

Current state and county rules in many areas limit

new docks to waters greater than a specific depth

at low tide, but many old docks are located in shallow water and have poorly defined access channels, if they have them at all. 

Many older access channels in open water are

subject to sedimentation and are maintained by

prop-dredging. Development is not just restricted

to uplands. The number of live-aboard vessels has

increased in some areas. Scarring of seagrasses by

hulls, anchors, and chains occurs as live-aboard

vessels (and other boats) swing at anchor over

shallow seagrass beds (Kruer 1994).

The increasing number of access points—

such as boat launching ramps—has also contributed to seagrass scarring. Boating-access areas

are usually located in sheltered areas, where seagrasses are more likely to occur. Hundreds of commercial marinas, watercraft rentals, and public

boat ramps are near shallow seagrass beds where

few channel markers exist. Because these channels

are usually subject to heavy sedimentation, regular

dredging is often needed to keep access open.

Some of the most severely scarred areas in Florida

are near marinas catering to flats fishermen in the

Florida Keys.

Management Options

When state funds for seagrass management are

limited, the money should be invested in those

counties that have the greatest acreage of M/Sscarred seagrasses (e.g., Monroe County).

However, if the severity of seagrass-habitat loss in

a county is related to the extent of seagrasses in

that county, then counties with both moderate seagrass acreage and more intense scarring may merit

similar attention when management programs are

being developed. Based on a scarring index (SI) in

which the relative percentage of M/S scarring in a

county is divided by the relative percentage of

total seagrass acreage for that county (Table 3), the

more threatened counties are Hillsborough (19.0),

Charlotte (18.4), Collier (13.0), Pinellas (10.2),

Manatee (9.4), Volusia (7.0), and Lee (6.9).

When assigning management priorities, however, other aspects of scarring extent must also be

considered. Because extensive areas of seagrasses

are in water depths greater than six feet, where

they are unlikely to be scarred, including these

acreages in SI calculations lessens the apparent

extent of scarring in some counties. If deeper seagrass beds are excluded from the SI calculations,

then county rankings would be considerably different. For example, Monroe County—which has a

high degree of M/S scarring—would rank low

using only an SI value because of the county’s
30 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Figure 11. Example of a channel serving a residential area and ending in a shallow seagrass bed.
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 31

extensive seagrass acreage, much of which is not

vulnerable to scarring. Therefore, common sense

must be used in determining where state management monies are spent. Basing decisions on

both the extent of M/S scarring and on an SI

value suggests that the principal foci for scarringmanagement programs should be Charlotte,

Dade, Hillsborough, Lee, Manatee, Monroe, and

Pinellas counties. Also ranking high in concern

are Brevard, Citrus, Collier, Pasco, and Volusia

counties.

Four-Point Approach

Ample justification now exists to reduce scarring

of seagrasses. A multifaceted approach is necessary to deal with the wide variety of user-groups,

activities, and types of physical perturbations.

Below is a four-point approach, used by some local

governments (e.g., Barker and Garrett 1992), that

can form the basis for an effective statewide management program. Effective implementation of

this comprehensive approach in plans designed

for specific locales should initially reduce seagrass

losses at moderately and severely scarred sites and

slow the increase in scarring at sites having only

light scarring. Modifications to management programs developed for specific areas should reduce

seagrass scarring, over the long term, to levels that

do not significantly affect habitat quality.

1. Education 

Education is an essential part of any effort to make

all boaters—tourists and residents alike—understand the sensitive nature of Florida’s shallow seagrass communities. Florida, with its millions of

visitors each year, is one of the most popular boating, diving, and fishing destinations in the world.

These boaters can be educated through informative pamphlets available at marinas and boaterregistration locations; through boating classes;

through boat-user’s guides and maps; through

public-school seminars; through signs at launching ramps; and through organizations such as the

Florida Conservation Association (FCA), the

Organized Fisherman of Florida (OFF), and the

U.S. Coast Guard Auxiliary and Power Squadron

(Kenworthy et al. 1988, Barker and Garrett 1992,

Folit and Morris 1992). Shallow-water fishing

guides and commercial fishermen—who have

strong interests in the health of Florida’s seagrass

resources—should use peer pressure to reduce any

scarring that is caused by their user-groups. Power

Squadron and Coast Guard Auxiliary boating

courses should include educational information on

the importance of seagrass beds and should

emphasize their protection as part of a safe-boating curriculum.

In areas where new visitors and seasonal residents are in continual flux, however, additional

approaches to accomplish resource-management

goals should be explored. Government agencies

need to be persistent in communicating the problem of seagrass scarring to the public. Single-year

efforts do not have the same effect on seasonal

populations—which change year to year—that

long-term, regular programs do. Aerial photographs that show scarred seagrass beds in

graphic detail have proven useful in educating

managers, decision-makers, and the public. This

approach could be used to communicate seagrassprotection needs to seasonal residents and tourists

at areas they are likely to visit (e.g., at boat-launching ramps). Communicating the need to limit the

size, draft, loads (tonnage), and power of vessels in

shallow seagrass beds is an important educational

goal.

2. Channel Marking (Aids to Navigation)

Conventional USCG-approved markers are helpful in deeper channels, but markers should be located away from the edges of shallow seagrass

flats to provide a wider buffer against scarring.

Markers should be gated (paired) in most locations

and should extend well beyond the ends of channels. Marking channels clearly—especially with

easily visible, reflective arrows—will benefit all

boaters by showing them the correct passage,

which would improve boating safety and at the

same time minimize incidental scarring of seagrasses by boaters who stray out of unmarked

channels.

Simple, easily installed and maintained markers with reflective directional arrows could be

effective deterrents to seagrass scarring but may

not conform to official USCG requirements. The

channel-marking system used by Everglades

National Park has directional arrows and is successful, but it needs some refinement (Skip Snow,

personal communication). Monroe County has addressed the need for additional channel marking
32 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

through their Department of Marine Resources,

which released a draft Boating Impact Management Plan (Barker and Garrett 1992). It will eventually be incorporated, in part, into the management plan for the Florida Keys National Marine

Sanctuary (FKNMS).

As channel-marking criteria are established

and new markers are put in place, illegal aids to

navigation should be removed. Often, channels are

prop-dredged through seagrasses and between

mangroves, even though an existing channel is

available just a short distance away. In some cases,

existing prop-dredged channels should be closed

off by installing reflective pilings to block access

and thus allow scarred seagrasses to recover. The

benefits to the resource brought by an effective

channel-marker system are negated if illegal markers and prop-dredged channels are allowed to proliferate.

3. Enforcement

Voluntary compliance has not proven effective in

the past in resolving many resource-damage problems. Prop-dredging and other vessel-related damage to seagrasses should be viewed as destruction

of protected public resources and as a form of

unsafe boating. Past actions by all levels of government provide legal authority to enforce rules

and regulations prohibiting prop-dredging (e.g.,

U.S.A. and FDER v. M.C.C. of Florida and

Michael’s Construction Co., Case No. 81-2373-CIVEBD, Southern District of Florida). Citations and

warnings for scarring seagrasses must be issued if

an enforcement program is to be effective. Scarring

of seagrasses would be substantially reduced, without placing undue hardship on the boating public,

if existing legal authority were fully exerted.

Scarring of seagrasses is often willful, particularly when it is repetitive. Florida has laws that

can protect natural resources from willful and

reckless damage (e.g., Reckless or careless operation of a vessel. F.S. 327.3; “Duty of the Board of

Trustees of the Internal Improvement Fund to protect, etc., state lands...”, F.S. 253.05; “State attorneys, other prosecuting officers of the state or

county...county sheriffs and their deputies...” to

assist in protecting state lands F.S. 253.04; and even

F.S. 380.05, “Areas of critical state concern...”). The

Florida Administrative Code, Chapter 18-14 discusses fines for damaging state lands.

4. Limited-Motoring Zones

Programs initiated by the FDEP, the U.S. Fish and

Wildlife Service, and several counties use moderate restrictions, such as idle-speed or limitedmotoring zones, to protect sensitive resources

while allowing public access compatible with

environmental protection. Shallow channels, flats,

and embayments near developed areas should be

protected before scarring problems become severe.

Areas set aside as preserves could be incorporated

into a zoning program that limits certain types of

access and offers protection (Barker and Garrett

1992). Weedon Island State Preserve (Pinellas

County) has experienced a 95 percent reduction in

the number of scars since it was closed to combustion engines—electric trolling motors are still

allowed—in October 1990 (Folit and Morris 1992).

Limited access and closure are effective ways

to reduce the scarring of seagrass beds; however,

many issues must be considered when closing

areas to watercraft. Work groups or task forces

should be created to address issues that concern

areas being considered for limited access or closure. Boating-effects studies, boating-use surveys,

and collaboration with affected parties must always be considered. Involving all sides in planning at the beginning is imperative when closing

an area to powered vessels. Task forces such as the

one for Cockroach Bay Aquatic Preserve

(Cockroach Bay Seagrass Task Force 1992) and the

one for Fort DeSoto Park in Pinellas County are

good examples of cooperation among user-groups

in formulating boat-access restrictions to protect

seagrasses.

The seagrass-management plan for Cockroach Bay Aquatic Preserve, located on the eastern

shore of Tampa Bay, was implemented by

Hillsborough County in August 1992. In certain

areas, the plan limits vessel access and prohibits

the use of combustion engines in waters that are

less than 18 inches deep at mean low water. Also,

the public is being educated using a number of approaches (e.g., through signs, posted at boatlaunching ramps, that discuss seagrass protection).

Channel markers will eventually have depth information posted. Law enforcement was increased in

the preserve by adding a Hillsborough County

Sheriff’s Deputy and by deputizing the manager of

the preserve. Seagrass recovery from scarring is

being studied, and aerial photography is being
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 33

used to monitor the amount of scarring in the preserve (Cockroach Bay Seagrass Task Force 1992).

Despite these steps, however, initial reports of

their effectiveness are in some respects disappointing. Scarring extents in Cockroach Bay have

increased by about 5000 linear feet in the first year

(Dawes et al. 1994). Also, around entrances to the

preserve, approximately 145,000 square feet of

additional scarring was discovered, despite its

cryptic nature (i.e., hidden by sedimentation).

Overall, an additional 3.3 acres of seagrasses were

scarred in one year within the preserve. In some

areas of the preserve, voluntary compliance has

not worked, and total closure has been implemented to alleviate scarring. Managers are looking into

further measures to reduce scarring losses, such as

proactive restoration and more rigorous regulation.

Pinellas County is implementing a similar

program for Fort DeSoto Park, which is near the

mouth of Tampa Bay. Motoring has been limited or

completely restricted in some areas. Fort DeSoto

Park has three types of limited-motoring zones: 1)

slow/minimum-wake zones are intended to improve

safety and reduce boat-wake effects, 2) seagrass

caution zones inform of seagrass presence and

encourage caution in boating, and 3) boat-restriction zones allow only poling and electric motoring.

As in Cockroach Bay Aquatic Preserve, semiannual aerial surveys will be conducted so that changes

in seagrass densities and scarring can be monitored and photographed for analysis. A final

report is being prepared on the effectiveness of the

program.

Concluding Remarks

Management programs to control seagrass scarring have been implemented by several local

governments. Additional programs are needed for

counties that have severe scarring problems.

Allocating monies for these programs may be a

low priority in some counties, however, and a

more general statewide program may be justified.

Currently, the state manages scarring in only a few

state parks (e.g., Lignumvitae Botanical Site and

John Pennecamp Coral Reef State Park). A statewide management program should be developed

to protect seagrasses from scarring while still

allowing for traditional water-related recreational

and commercial activities. Combined with county

programs, statewide management of scarring

could effectively protect seagrass habitat.

Overregulating where scarring does not substantially alter system productivity may strain

government budgets and needlessly irritate those

attempting to enjoy the resource. Therefore, focusing resources in areas that are extensively scarred

or that are vulnerable to increased scarring is of

paramount importance. Educating the public

about the more severely scarred areas will also

reduce the extent of light scarring in other areas as

citizens are made aware of the value of seagrasses.

Nevertheless, management plans should ensure

that site-specific seagrass protection does not shift

M/S scarring to other, less scarred areas.

A single management approach, such as

channel-marking alone, only partially addresses

the problem of seagrass scarring. A combination of

management techniques, along with long-term

commitment, must be used to reduce the frequency and degree of scarring in seagrass beds. Some

programs being implemented and tested use

multifaceted approaches such as better educating

the boating public, better marking of channels,

limiting powerboat access in certain sensitive

areas, and more effectively enforcing existing laws.

Monitoring managed areas, both from the air and

on site, is critical in determining the effectiveness

of a management program.

Florida’s waters are of special value for many

reasons and are important at a national as well as

state level. Florida’s fishing industries depend on

the health and vitality of shallow seagrass beds, as

do diverse animal species—many of which are of

endangered, threatened, or sensitive status. With

the loss of seagrasses to scarring comes degradation and loss of critical animal habitat and, in some

areas, a decrease in water quality. Nevertheless,

preventing all seagrass scarring is impossible. With

proper management, scarring can be reduced to a

level that will reverse the cumulative damage to

this critical resource. This report contributes

knowledge that was lacking in past regulatory and

management programs mandated to protect

Florida’s marine resources. Although the data presented in this report are of a broad nature, the

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impacts on seagrass meadows in Florida. Pp.

139–151 in Durako, M.J., R.C. Phillips, and R.R.

Lewis, III (eds.). Proceedings of the Symposium on

Subtropical-Tropical Seagrasses of the Southeastern

United States. Fl. Mar. Res. Pub. 42. St. Petersburg,

FL. 209 p.

MATTHEWS, T.R., A.C. LAZAR, AND J.H. HUNT.

1991. Aerial observations of boating impacts to

shallow water grass beds in the Florida Keys. Rep.

to Fla. Dept. Nat. Res., Off. Mar. Prog. Plan.

Tallahassee, FL. 12 p.

ONUF, C.P. 1991. Light requirements of Halodule

wrightii, Syringodium filiforme, and Halophila engelmanni in a heterogeneous and variable environment inferred from long-term monitoring. Pp.

87–97 in Kenworthy, W.J. and D. Haunert (eds.),

The capability of water quality criteria, standards

and monitoring programs to protect seagrasses

from deteriorating water transparency. Results

and recommendations of a workshop held

January 30, 1991 in West Palm Beach, FL.

Submitted to NOAA Coast. Ocean Prog. Est.

Habitat Stud. 151 p.

PHILLIPS, R.C. 1960. Observations on the ecology

and distribution of the Florida seagrasses. Fl. State

Board Conserv. Mar. Lab., Prof. Papers Ser. 2. St.

Petersburg, FL. 72 p.

TERRY, R.D. AND G.V. CHILINGAR. 1955.

Comparison charts for visual estimation of percent composition. Allen Hancock Foundation. Los

Angeles, CA. Reprinted from J. Sed. Petrology

23:226–234.

THAYER, G.W., D.A. WOLFE, AND R.B.

WILLIAMS. 1975. The impact of man on seagrass

systems. Am. Sci. 63:288–296.

U.S. DEPARTMENT OF THE INTERIOR. 1973.

Resource and Land Information for South Dade

County, Florida. U.S. Geological Survey

Investigation I-850.

WILDERNESS SOCIETY, FLORIDA KEYS AUDUBON

SOCIETY, AND LEWIS ENVIRONMENTAL SERVICES,

INC. 1990. Is uncontrolled boating damaging

thousands of acres of Florida’s submerged seagrass meadows? The Boating Impact Work Group.

Marathon, FL. 34 p.

WOODBURN K.D., B. ELDRED, E. CLARK, F.

HUTTON, AND R.M.INGLE. 1957. The live bait

shrimp fishery of the west coast of Florida (Cedar

Key to Naples). Fl. State Board Conserv. Mar. Lab.

Tech. Ser. 21. St. Petersburg, FL. 33 p.
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 37

ZIEMAN, J.C. 1976. The ecological effects of physical damage from motor boats on turtle grass beds

in southern Florida. Aquat. Bot. 2:127–139.

ZIEMAN, J.C. AND R.T. ZIEMAN. 1989. The ecology of

the seagrass meadows of the west coast of Florida:

A community profile. U.S. Fish Wildlife Serv. Biol.

Rep. 85 (7.25). 155 pp.
APPENDIX A
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 41

MRGIS Integration

Geographic Information Systems (GIS) and related

technologies have emerged as fundamental tools

for synthesizing and analyzing complex spatial

and statistical data. In our study, the final data

taken from paper maps and charts were integrated

into the Marine Resources GIS (MRGIS) at the

Florida Marine Research Institute (FMRI) by the

Coastal and Marine Resources Assessment

(CAMRA) group.

In consideration of the geographic extent of

the study, the varied scales of the base maps, and

the data-collection methodology, CAMRA staff

determined that the data would be better represented as a single, statewide coverage with a scale

of 1:40,000. One factor that significantly influenced

that decision was the existence of a 1:40,000-scale

land coverage already within the MRGIS. Using

this land coverage, digitization effort was minimized without substantially compromising the

integrity of the information. The polygons delineating scarring were digitized and attributed to

their appropriate scarring intensities. The resultant

scarring coverage was registered to the 1:40,000-

scale shoreline coverage.

After completing the digitization and attribution process, check plots were produced and compared to the original source maps to verify the

presence and proper attribution of the polygons.

Polygons that were inadvertently omitted from the

coverage were added, and incorrect attributes

were changed. A second iteration of this qualityassurance process was performed to ensure the

completeness of these preliminary data on scarring.

In the next step of the integration process, we

used the 1:40,000-scale land coverage to erase any

portion of a polygon that had been drawn onto the

land and subsequently digitized. Erase is an

ARC/INFO command that creates a new coverage

by removing portions of the polygons from one

coverage that are within an erase region. In this

case, the polygons in the land coverage define that

erase region, and the portions of the digitized polygons that overlapped the land were removed. In

essence, this procedure removed any portion of a

polygon that was coincident with a land feature.

This process was used to ensure the appropriate

spatial coincidence between the polygons and the

land features without having to digitize them. This

minimized operator error on subsequent areal

comparisons by ensuring coincidence of all arcs

with other data sets contained in the MRGIS.

Following the erase process, the resultant coverage was intersected with a modified county coverage and used to calculate acreages scarred by

class and county. Intersect is one of several overlay

commands available in ARC/INFO. Intersect was

used because the polygons in the coverage (input

coverage) split where the polygons of the county

boundaries (intersect coverage) overlap. Only

those portions of polygons coincident between

both input and intersect coverages were saved in

the output coverage. All feature-attribute items

from both coverages were carried in the attribute

tables of the output coverage. If duplicate items

were encountered, the item from the input coverage was maintained, and the one in the intersect

coverage was dropped.

The original county coverage was obtained

from the 1990, 1:100,000 TIGER census data for the

state of Florida. The shoreline features were

removed, and where required, the county boundaries were extended offshore to enclose the data

just created and all the existing seagrass-distribution data. On the Atlantic coast, the three-mile offshore extensions of the original County

Jurisdictional Boundaries were sufficient to meet

our standards. On the Gulf coast, county boundaries were extended out to the nine-mile State

Jurisdictional line. For Dade and Monroe counties,

the offshore lines required further extension to

ensure enclosure of all mapped seagrasses.

Creating a Statewide Seagrass Coverage

A statewide seagrass database consisting of the

most recent seagrass data available was assembled. Data were obtained from various sources and

integrated into the MRGIS (Appendix Table 1).

Disparate seagrass data sets from such a wide variety of sources created integration difficulties. Data

collected were of various dates, scales, seagrass

classifications, and formats. For example, seagrass

classifications ranged from species-specific values

for the density of bottom cover to unique coding

schemes. Although data created in-house or by one

Methodology for Analyzing Scar Data
42 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

of the water-management districts were in

ARC/INFO format, data from some sources were

AutoCAD line files, which required conversion.

This situation is not unique to this study. GIS and

remote-sensing disciplines are currently investigating theoretical and technical difficulties associated with integrating data from disparate sources.

Some seagrass source data were distorted and

required correction (e.g., data for Charlotte Harbor

and the Big Bend region). In addition to correcting

existing seagrass data sets and integrating nonARC/INFO data, several gaps in the statewide

seagrass-data coverage were identified and filled.

Data needs for the area from Indian Rocks Beach to

Anclote Key and a portion of Sarasota Bay were

filled using 1990 SWFWMD 1:24,000-scale CIR

aerials. Some minor gaps in the seagrass data from

south Florida and the southern half of Estero Bay

were interpreted from 1:24,000-scale CIR aerials

borrowed from the SFWMD. The final statewide

seagrass coverage was created in such a way that

all of the seagrass attributes were combined and

simplified to a single code that indicated presence

or absence of seagrass. This coverage was then

intersected with the same county coverage

described above and used to calculate an acreage

of mapped seagrasses for each coastal county represented in this study.

Appendix Table 1. Sources of data used to compile seagrass distributions for the 31 Florida coastal

counties in this study.

Coverage Counties Included Date Scale Source Name*

BENDGRASS Citrus, Hernando, Jefferson, 1983 1:40,000 Minerals Management Service 

Levy, Pasco, Pinellas, Taylor (MMS)

CHARGRASS Charlotte, Collier, Lee, 1982, 1987 1:24,000 Florida Dept. of Transportation,

Manatee, Sarasota Florida Dept. of Environmental

Protection, Mangrove Systems, 

Inc., FMRI

IRLGRASS Brevard, Broward, Indian 1992 1:24,000 St. Johns River Water

River, Martin, St. Lucie, Management District

Volusia

PALMGRASS Martin, Palm Beach 1990 1:24,000 Palm Beach County

PANGRASS Bay, Escambia, Franklin, 1982–1985 1:24,000 FMRI

Gulf, Okaloosa, Santa Rosa, 

Wakulla, Walton

SFGRASS Dade, Monroe 1982–1986 1:40,000 Marszalek, Dade County, 

MMS, FMRI

TBAYGRASS Hillsborough, Manatee, 1990 1:24,000 Southwest Florida Water 

Pinellas, Sarasota Management District, FMRI

* Identifying name for seagrass-coverage data in the Marine Resources Geographic Information System at the Florida Marine

Research Institute (FMRI).
F.J. Sargent et al. 1995 Scarring of Florida’s Seagrasses

FMRI Technical Report TR-1 43

Error Reduction

A mapping effort of this scale and geographic

extent cannot contain sufficient detail to account

for subtle changes in bottom type. In many cases,

polygons were not exclusively coincident with seagrasses but included areas of bare substrate, tidal

flats, hardbottom, and channels. To evaluate the

ramifications of this phenomenon, a comprehensive assessment of the potential overestimation of

scarring was conducted, and suspect areas were

identified. A new series of 1:40,000-scale checkplots were created that overlaid the erased polygons on the presence-absence seagrass data now

contained in the MRGIS.

Digital coverages were combined and analytic tools in the GIS were used to calculate the degree

of coincidence and shrinkage. Shrinkage describes

the reduction in size of polygons so that they coincided with known seagrass-distribution data

already in the MRGIS. In some regions of the state

(e.g., the Big Bend region), the differences between

the original scarring calculated and the corrected

scarring values were minimal (coincidence

approximately 100 percent). However, in other

areas (e.g., Tampa Bay), corrected values decreased

the original scarring calculations by nearly 40 percent. A series of 1:40,000-scale test plots were run

to evaluate the cause of this variability and to

determine if our correction methodology was

sound.

Variability between areas can be explained by

several factors. For areas such as Tampa Bay—

where the seagrass data were mapped with a high

level of detail from high-resolution aerial photography (1:24,000)—polygons could be corrected

with a great deal of confidence. In contrast, for

regions like the Big Bend—where seagrass data

were mapped from less detailed, smaller-scale

photography—polygons were almost completely

coincident with mapped seagrasses, and shrinkage

was minimal. Seagrass distributions also affected

the amount of correction needed. The more discontinuous (the patchier) the seagrass beds were,

the greater the shrinkage was. Similarly, the

shrinkage may be adversely affected by temporal

differences between the seagrass source data and

data from the aerial surveys. For example, seagrass-distribution data used in Charlotte Harbor

date back to 1982, ten years before the aerial surveys were conducted for this study. Changes in

seagrass distribution probably occurred during

that time period. The effects of these potential

influences could not be controlled with the

methodological approach used in this study.

Polygons coincident with mapped seagrasses

were categorized as Type I. Despite the shrinkage

method used, these polygons would have

remained in the data. In areas with questionable

seagrass and scarring coincidence, each case was

individually evaluated for accuracy. Most of the

assessment in the Florida Keys was accepted without secondary evaluation because the survey was

done under the auspices of the FMRI, and polygons that were generated were subjectively classified as Type II. Polygons were classified as Type II

if they were not coincident with pre-existing,

mapped seagrass distributions but were obviously

present as part of existing seagrasses. Type-II polygons were included in the final data on scarring.
APPENDIX B
46 FMRI Technical Report TR-1

Scarring of Florida’s Seagrasses F.J. Sargent et al. 1995

Geographic-Distribution Charts

Figures B-1 to B-13 show the geographic distributions of seagrasses and scarring in the 31 Florida

coastal counties in this study. On each map are

two pie diagrams for each county. The pie labeled

County shows the percentage of scarring in each

intensity category in that county. Consult Table 2 

for acreages and Table 4 for percentages. The pie

labeled State shows the percentage of scarring in

that county for each intensity category relative to

the total acreage of scarring in the state for each

intensity category. Consult Table 3 for relative

percentages for each county.

Figure B1. Scar-distribution map—Escambia, Santa Rosa, Okaloosa counties

Figure B2. Scar-distribution map—Walton, Bay, Gulf counties

Figure B3. Scar-distribution map—Franklin, Wakulla, Jefferson counties

Figure B4. Scar-distribution map—Taylor, Dixie counties

Figure B5. Scar-distribution map—Levy, Citrus, Hernando counties

Figure B6. Scar-distribution map—Pasco, Pinellas, Hillsborough counties

Figure B7. Scar-distribution map—Manatee, Sarasota, Charlotte counties 

Figure B8. Scar-distribution map—Lee, Collier counties

Figure B9. Scar-distribution map—Monroe County 

Figure B10. Scar-distribution map—Dade, Broward counties

Figure B11. Scar-distribution map—Palm Beach, Martin counties

Figure B12. Scar-distribution map—St. Lucie, Indian River counties

Figure B13. Scar-distribution map—Brevard, Volusia counties
Escambia

Santa Rosa

Okaloosa

5 0 5 10

KILOMETERS

5 0 5 10

State

MILES

County

County

State

State

County

Alabama

Gulf of

Mexico

Pensacola Bay Choctawhatchee Bay

Perdido Bay

Scale 1:500,000

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

Figure B1.

LandNonseagrass Waters“Nonscarred” SeagrassLight ScarringModerate ScarringSevere ScarringSeagrass OutsideCounties of InterestPropeller Scars OutsideCounties of Interest
Walton

Bay

Gulf

5 0 5 10

KILOMETERS

5 0 5 10

MILES

SCALE 1:200,000

State

County

County

State

State

County

Gulf

of

Mexico

Choctawhatchee Bay

St. Andrew

Bay

St. Joseph

Bay

Scale 1:500,000

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

Figure B2.

LandNonseagrass Waters“Nonscarred” SeagrassLight ScarringModerate ScarringSevere ScarringSeagrass OutsideCounties of InterestPropeller Scars OutsideCounties of Interest
Franklin

Wakulla

Jefferson

5 0 5 10

KILOMETERS

5 0 5 10

MILES

SCALE 1:200,000

Apalachicola Bay

Apalachee Bay

State

County

County

State

State County

Gulf of Mexico

Scale 1:500,000

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

Figure B3.

LandNonseagrass Waters“Nonscarred” SeagrassLight ScarringModerate ScarringSevere ScarringSeagrass OutsideCounties of InterestPropeller Scars OutsideCounties of Interest
Taylor

Dixie

5 0 5 10

KILOMETERS

5 0 5 10

MILES

SCALE 1:200,000

State

County

State

County

Gulf

of

Mexico

Scale 1:500,000

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

Figure B4.

Land

Nonseagrass Waters

“Nonscarred” Seagrass

Light Scarring

Moderate Scarring

Severe Scarring

Seagrass Outside

Counties of Interest

Propeller Scars Outside

Counties of Interest
Levy

Citrus

Hernando

5 0 5 10

KILOMETERS

5 0 5 10

MILES

State

County

State

County

Gulf

of

Mexico

Scale 1:500,000

State

County

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

Figure B5.

Land

Nonseagrass Waters

“Nonscarred” Seagrass

Light Scarring

Moderate Scarring

Severe Scarring

Seagrass Outside

Counties of Interest

Propeller Scars Outside

Counties of Interest
Pasco

Pinellas

Hillsborough

5 0 5 10

KILOMETERS

5 0 5 10

MILES

State

County

State

County

Gulf

of

Mexico

Scale 1:500,000

State

County

Tampa Bay

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

Figure B6.

Land

Nonseagrass Waters

“Nonscarred” Seagrass

Light Scarring

Moderate Scarring

Severe Scarring

Seagrass Outside

Counties of Interest

Propeller Scars Outside

Counties of Interest
Manatee

Sarasota

Charlotte

5 0 5 10

KILOMETERS

5 0 5 10

MILES

State

County

State

County

Gulf

of

Mexico

Scale 1:500,000

State

County

Charlotte Harbor

Tampa Bay

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

Figure B7.

Land

Nonseagrass Waters

“Nonscarred” Seagrass

Light Scarring

Moderate Scarring

Severe Scarring

Seagrass Outside

Counties of Interest

Propeller Scars Outside

Counties of Interest
Lee

Collier

5 0 5 10

KILOMETERS

5 0 5 10

MILES

SCALE 1:200,000

State

County

State

County

Gulf

of

Mexico

Scale 1:500,000

Charlotte Harbor

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

Figure B8.

Land

Nonseagrass Waters

“Nonscarred” Seagrass

Light Scarring

Moderate Scarring

Severe Scarring

Seagrass Outside

Counties of Interest

Propeller Scars Outside

Counties of Interest
Monroe

5 0 5 10

KILOMETERS

5 0 5 10

MILES

SCALE 1:200,000

match line

match line

Key West

Marathon

State

County

Gulf of

Mexico

Scale 1:500,000

Everg
Key Largo

Atlantic Ocean

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

Biscayne Bay

Figure B9.

glades National Park

Land

Nonseagrass Waters

“Nonscarred” Seagrass

Sparse/Hardbottom

Light Scarring

Moderate Scarring

Severe Scarring

Seagrass Outside

Counties of Interest

Propeller Scars Outside

Counties of Interest
Dade

Broward

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

5 0 5 10

KILOMETERS

5 0 5 10

MILES

SCALE 1:200,000

State

County

State

County

Scale 1:500,000

Figure B10.

Biscayne Bay

Land

Nonseagrass Waters

“Nonscarred” Seagrass

Sparse/Hardbottom

Light Scarring

Moderate Scarring

Severe Scarring

Seagrass Outside

Counties of Interest

Propeller Scars Outside

Counties of Interest
Palm Beach

Martin

5 0 5 10

KILOMETERS

5 0 5 10

MILES

SCALE 1:200,000

State

County

State

County

Scale 1:500,000

Atlantic Ocean

St Lucie River

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

Figure B11.

Land

Nonseagrass Waters

“Nonscarred” Seagrass

Light Scarring

Moderate Scarring

Severe Scarring

Seagrass Outside

Counties of Interest

Propeller Scars Outside

Counties of Interest
St. Lucie

Indian River

5 0 5 10

KILOMETERS

5 0 5 10

MILES

SCALE 1:200,000

State

County

State

County

Scale 1:500,000

Atlantic Ocean

St Lucie River

Lake Okeechobee

Indian

River

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

Figure B12.

Land

Nonseagrass Waters

“Nonscarred” Seagrass

Light Scarring

Moderate Scarring

Severe Scarring

Seagrass Outside

Counties of Interest

Propeller Scars Outside

Counties of Interest
Volusia

Brevard

5 0 5 10

KILOMETERS

5 0 5 10

MILES

SCALE 1:200,000

State

County

State

County

Scale 1:500,000

Atlantic Ocean

Indian River

Banana

River

Mosquito

Lagoon

Lagoon

Gulf

of

Mexico

Atlantic

Ocean

Alabama Georgia

E

N

W

S

Figure B13.

Land

Nonseagrass Waters

“Nonscarred” Seagrass

Light Scarring

Moderate Scarring

Severe Scarring

Seagrass Outside

Counties of Interest

Propeller Scars Outside

Counties of Interest