# 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 andshellfish 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.



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## Table of Contents

L IST OF 

### T ABLES



### ............................................................................................................................... ......... ii

L IST OF 

### F IGURES



### ............................................................................................................................... ...... iii

A CKNOWLEDGMENTS



### .............................................................................................................................. iv

E XECUTIVE 

### S UMMARY



### .............................................................................................................................. v

I NTRODUCTION



### ............................................................................................................................... .......... 1
Seagrass Recovery ...................................................................................................................... 5 Study Objectives ........................................................................................................................ 7

M ETHODS



### ............................................................................................................................... .................. 7
Scarring Recognition ................................................................................................................... 9
Scar Mapping ............................................................................................................................ 10

R ESULTS



### ............................................................................................................................... ................... 12

D ISCUSSION



### ............................................................................................................................... ............. 24

M ANAGEMENT 

### O PTIONS 

### ........................................................................................................................ 29 Four-Point Approach ............................................................................................................... 31

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

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

C ONCLUDING 

### R EMARKS 

### ........................................................................................................................ 33

L ITERATURE 

### C ITED



### ............................................................................................................................... .. 35

A PPENDIX 

### A .............................................................................................................................. ............. 39 Methodology for Analyzing Scar Data .................................................................................... 41
MRGIS Integration ......................................................................................................... 41 Creating a Statewide Seagrass Coverage .................................................................... 41

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

A PPENDIX 

### 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



### A PPENDIX 

### 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



### A PPENDIX 

### 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’scoastal ecology and economy; they provide nutrition and shelter to animals important to marine fisheries, provide critical habitat for many otheranimals (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 bescarred by many activities, but scars are most commonly made when a boat’s propeller tears and cutsup 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 ofscarred 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, whichwere 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. Theinformation acquired in this survey was incorporated into the FMRI’s Marine Resources Geographic Information System (MRGIS), whichproduces 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 situationsthat 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 ownpersonal 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’sdesigned 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 beeninstituted 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 mayneed 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 baresediments 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 Atlanticcoast. 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 ofturtle-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 andwidgeon-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 indeeper waters, especially in the Gulf of Mexico offshore of Florida’s Big Bend region. The numerous plants and animals that liveand grow among seagrasses form a complex, fragile community. Marine and estuarine animals— especially larval and juvenile fish—benefit fromseagrasses, which provide critical shelter and sustenance. Seagrasses form some of the most productive communities in the world (Zieman andZieman 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 itsseafood (Thayer et al. 1975). In addition, seagrasses improve water quality by stabilizing mobile sediments and by incorporating some pollutantsinto plant biomass and into the stabilized sediments. As Florida’s population increases, particularlyin 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 isshallower 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 seagrassbeds, 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 the1970s, 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 ofseagrass 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 withmore 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 strongindicator 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. Asmaller 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. Sometimesboaters are aware of but unconcerned about seagrasses and therefore do not avoid scarring them; A conscientious boater who trims his motor mayonly 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 ofcumulative loss. This can result in the resuspension of sediments in the water column, which may further contribute to habitat loss by inhibiting thegrowth 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 shownthat each of Florida’s seagrass species has structural and physiological differences that affect theirgrowth 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 morequickly than turtle-grass does because shoalgrass has a shallower rhizome system and growswell 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 18inches deep into seagrass beds indicated that seagrasses may recover slowly from scarring (Jones 1968 cited in Zieman 1976, Godcharles 1971). Thetrenches 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 amore recent study, Durako et al. (1992) used a linear-regression model to predict that individualscars 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/m 2 ) but that turtle-grass takes approximately 3.6–6.4 years toachieve normal density (400–700 shortshoots/m 2 ). At the sparser edges of shoal-grass beds, however, recovery times (2.3–4.6 years) approached those of turtle-grass, probably becauseof 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 mustremain free of additional scarring, and other environmental conditions must be favorable for plant survival and growth. Even so, the recovery periodfor scarred seagrass beds (especially for turtlegrass) averages at least three to five years and isprobably 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 variablesthat 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. Sedimentproperties 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 southFlorida 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 localconditions 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, itcan 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 freshwater, 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 lightreduction 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 inseagrasses. 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 tohigher 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 qualityof 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 7affects 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 turbidwater. 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 bystrong winds and waves, especially during extremely low tides. Boat wakes can also scour scarred areas. Kenworthy et al. (1988) concludedthat boat-wake waves substantially elevate bottom-shear stress along shallow seagrass beds and seriously jeopardize seagrass health.

Study ObjectivesSlow 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 theFlorida 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 developingappropriate 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 usinga 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 thatFlorida’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, weused an approach combining analysis of high-resolution aerial photographs with ground-truthingduring 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 FloridaKeys, and then north along the lagoonal river systems of the Atlantic Coast to just south of New Smyrna Beach (Volusia County) in MosquitoLagoon. 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. Individualprop-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 thatthe 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 ofscars 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 appropriatewater-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 theU.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. TheSt. 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 thePanhandle 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, comparingmaps of different scales should be done with caution. Large-scale photography (e.g., 1:2,400) cangive 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 culturaldata, and subtle differences in county-line boundaries could alter conclusions if the data are used too strictly in detailed comparisons. Therefore, weurge caution when making comparisons of the differences between regions and between counties.

Scarring RecognitionScarring 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 dueto 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—suchas the Ten Thousand Islands and the Chassa-howitzka and Crystal rivers—delineating small polygons was impossible at the available map scales; asa 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 between1 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. Anoblique 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 ofscarred 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 toNational Oceanic and Atmospheric Administration (NOAA) nautical charts using a zoom transfer scope (ZTS). The ZTS superimposes an image ontoa 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 1992and 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 werephotographed, 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 (Cessna152 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 scarringintensity. 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 scarsthrough 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 InformationSystem (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 13is uneven; some counties have very little and others have a disproportionately large amount (seefigures in Appendix B). Monroe County alone contains 54.6 percent of all Florida seagrass-bed acreage—mostly in Florida Bay and the FloridaKeys (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 coalescenceof 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) isfairly 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

B AY 10,530 4,050 820 80 900 4,950 B REVARD 46,190 4,160 1,940 110 2,050 6,210 B ROWARD 0 (1) 0 0 0 0 0 C HARLOTTE 14,190 1,530 5,630 290 5,910 7,440 C ITRUS 147,810 25,700 1,700 180 1,880 27,580 C OLLIER 5,250 1,970 1,590 90 1,680 3,650 DADE 145,650* 2,740 3,970 4,500 8,480 11,220 D IXIE 111,130 2,470 1,020 0 1,020 3,490 E SCAMBIA 2,750 510 180 10 190 700 F RANKLIN 19,840 440 370 0 370 810 G ULF 8,170 4,200 530 110 640 4,840 H ERNANDO 146,870 7,790 710 0 710 8,500 H ILLSBOROUGH 6,320 1,680 2,230 180 2,410 4,090 I NDIAN R IVER 2,940 140 10 30 40 180 J EFFERSON 10,500 420 80 0 80 510 L EE 50,510 5,930 7,100 1,290 8,390 14,310 L EVY 132,400 9,970 120 0 120 10,090 M ANATEE 12,160 2,480 2,200 780 2,990 5,470 M ARTIN 2,310 20 10 0 10 30 M ONROE 1,452,800* 14,560 10,430 5,060 15,490 30,050 O KALOOSA 3,450 310 80 0 (5) 80 390 P

ALM B EACH 2,510 50 20 0 20 70 P

ASCO 85,570 2,120 1,760 360 2,120 4,240 P INELLAS 22,920 3,800 3,870 2,010 5,880 9,680 S ANTA R OSA 2,720 450 110 0 110 560 S ARASOTA 4,160 720 300 30 330 1,050 S T. L UCIE 6,920 40 40 0 40 80 T

AYLOR 162,860 8,100 60 0 60 8,160 V

OLUSIA 8,490 1,430 1010 350 1,370 2,800 W

AKULLA 29,630 2,060 730 0 730 2,790 W

ALTON 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 explana

tion. The total area of moderately dense, dense, and contiguous seagrasses for the state is 1,900,960 acres, excluding hardbott om 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 inthis 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

B AY 0.4 3.7 1.7 0.5 1.4 2.8 B REVARD 1.7 3.8 4.0 0.7 3.2 3.6 B ROWARD 0.0 0.0 0.0 0.0 0.0 0.0 C HARLOTTE 0.5 1.4 11.6 1.9 9.2 4.3 C ITRUS 5.6 23.4 3.5 1.1 2.9 15.8 C OLLIER 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 D IXIE 4.2 2.2 2.1 0.0 1.6 2.0 E SCAMBIA 0.1 0.5 0.4 0.1 0.3 0.4 F RANKLIN 0.8 0.4 0.8 0.0 0.6 0.5 G ULF 0.3 3.8 1.1 0.7 1.0 2.8 H ERNANDO 5.5 7.1 1.5 0.0 1.1 4.9 H ILLSBOROUGH 0.2 1.5 4.6 1.2 3.8 2.4 I NDIAN R IVER 0.1 0.1 0.0 0.2 0.1 0.1 J EFFERSON 0.4 0.4 0.2 0.0 0.1 0.3 L EE 1.9 5.4 14.6 8.3 13.1 8.2 L EVY 5.0 9.1 0.2 0.0 0.2 5.8 M ANATEE 0.5 2.3 4.5 5.1 4.7 3.1 M ARTIN 0.1 0.0 0.0 0.0 0.0 0.0 M ONROE 54.6 13.2 21.4 32.7 24.2 17.3 O KALOOSA 0.1 0.3 0.2 0.0 0.1 0.2 P

ALM B EACH 0.1 0.0 0.0 0.0 0.0 0.0 P

ASCO 3.2 1.9 3.6 2.3 3.3 2.4 P INELLAS 0.9 3.5 8.0 13.0 9.2 5.6 S ANTA R OSA 0.1 0.4 0.2 0.0 0.2 0.3 S ARASOTA 0.2 0.6 0.6 0.2 0.5 0.6 S T. L UCIE 0.3 0.0 0.1 0.0 0.1 0.0 T

AYLOR 6.1 7.4 0.1 0.0 0.1 4.7 V

OLUSIA 0.3 1.3 2.1 2.3 2.1 1.6 W

AKULLA 1.1 1.9 1.5 0.0 1.1 1.6 W

ALTON 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; approximatelyone 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 acounty 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, countiesmust 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 fromseagrass 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 theBig 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 datawere based on different definitions for sparse seagrass or included patchy (but dense) seagrasseswithin a polygon. In this study, sparse and hardbottom seagrasses in Monroe and Dade counties were included in the overall seagrass distributionsbecause 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 toeliminate these categories from scarring-extent calculations. All of our calculations were based on thetotal 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 wehave attempted to reduce distribution errors, inaccuracies remain because of the broad nature ofthis 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

B AY 10,530 38.4 7.8 0.7 8.5 47.0 B REVARD 46,190 9.0 4.2 0.2 4.4 13.4 B ROWARD 1 100.0 0.0 0.0 0.0 100.0 C HARLOTTE 14,190 10.8 39.6 2.0 41.6 52.4 C ITRUS 147,810 17.4 1.2 0.1 1.3 18.7 C OLLIER 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 D IXIE 111,130 2.2 0.9 0.0 0.9 3.1 E SCAMBIA 2,750 18.7 6.4 0.3 6.7 25.4 F RANKLIN 19,840 2.2 1.9 0.0 1.9 4.1 G ULF 8,170 51.4 6.6 1.3 7.9 59.3 H ERNANDO 146,870 5.3 0.5 0.0 0.5 5.8 H ILLSBOROUGH 6,320 26.6 35.3 2.9 38.2 64.8 I NDIAN R IVER 2,940 4.8 0.3 1.1 1.4 6.2 J EFFERSON 10,500 4.0 0.8 0.0 0.8 4.8 L EE 50,510 11.7 14.1 2.6 16.7 28.4 L EVY 132,400 7.5 0.1 0.0 0.1 7.6 M ANATEE 12,160 20.4 18.1 6.5 24.6 45.0 M ARTIN 2,310 1.0 0.4 0.0 0.4 1.4 M ONROE 1,452,800 1.0 0.7 0.4 1.1 2.1 O KALOOSA 3,450 9.0 2.2 0.1 2.3 11.3 P

ALM B EACH 2,510 2.1 0.9 0.0 0.9 3.0 P

ASCO 85,570 2.5 2.1 0.4 2.5 5.0 P INELLAS 22,920 16.6 16.9 8.8 25.7 42.3 S ANTA R OSA 2,720 16.4 4.1 0.0 4.1 20.5 S ARASOTA 4,160 17.2 7.2 0.8 8.0 26.0 S T. L UCIE 6,920 0.6 0.6 0.0 0.6 1.2 T

AYLOR 162,860 5.0 0.0 0.0 0.0 5.0 V

OLUSIA 8,490 16.9 11.9 4.2 16.1 33.0 W

AKULLA 29,630 6.9 2.5 0.0 2.5 9.4 W

ALTON 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 M ONROE C ITRUS M ONROE M ONROE M ONROE M ONROE 2 T AYLOR M ONROE L EE D ADE D ADE C ITRUS 3 C ITRUS L EVY C HARLOTTE P INELLAS L EE L EE 4 H ERNANDO T AYLOR D ADE L EE C HARLOTTE D ADE 5 D ADE H ERNANDO P INELLAS M ANATEE P INELLAS L EVY 6 L EVY L EE H ILLSBOROUGH P ASCO M ANATEE P INELLAS 7 D IXIE G ULF M ANATEE V OLUSIA H ILLSBOROUGH H ERNANDO 8 P ASCO B REVARD B REVARD C HARLOTTE P ASCO T AYLOR 9 L EE B AY P ASCO C ITRUS B REVARD C HARLOTTE 10 B REVARD P INELLAS C ITRUS H ILLSBOROUGH C ITRUS B REVARD 11 W AKULLA D ADE C OLLIER B REVARD * C OLLIER M ANATEE 12 P INELLAS * M ANATEE D IXIE G ULF * V OLUSIA B AY 13 F RANKLIN * D IXIE V OLUSIA C OLLIER * D IXIE G ULF 14 C HARLOTTE * P ASCO B AY B AY * B AY P ASCO 15 M ANATEE * W AKULLA W AKULLA I NDIAN R IVER * W AKULLA H ILLSBOROUGH 16 B AY * C OLLIER H ERNANDO S ARASOTA * H ERNANDO C OLLIER 17 J EFFERSON * H ILLSBOROUGH G ULF E SCAMBIA * G ULF D IXIE 18 G ULF * C HARLOTTE F RANKLIN * B ROWARD * F RANKLIN * V OLUSIA 19 V OLUSIA * V OLUSIA S ARASOTA * D IXIE * S ARASOTA * W AKULLA 20 S T . L UCIE * S ARASOTA * E SCAMBIA * F RANKLIN * E SCAMBIA * S ARASOTA * 21 H ILLSBOROUGH * E SCAMBIA * L EVY * H ERNANDO * L EVY * F RANKLIN * 22 C OLLIER * S ANTA R OSA * S ANTA R OSA * J EFFERSON * S ANTA R OSA * E SCAMBIA * 23 S ARASOTA * F RANKLIN * J EFFERSON * L EVY * J EFFERSON * S ANTA R OSA * 24 O KALOOSA * J EFFERSON * O KALOOSA * M ARTIN * O KALOOSA * J EFFERSON * 25 I NDIAN R IVER * O KALOOSA * T AYLOR * O KALOOSA * T AYLOR * O KALOOSA * 26 E SCAMBIA * I NDIAN R IVER * S T . L UCIE * P ALM B EACH * I NDIAN R IVER * I NDIAN R IVER * 27 S ANTA R OSA * P ALM B EACH * P ALM B EACH * S ANTA R OSA * S T . L UCIE * S T . L UCIE * 28 P ALM B EACH * S T . L UCIE * I NDIAN R IVER * S T . L UCIE * P ALM B EACH * P ALM B EACH * 29 M ARTIN * M ARTIN * M ARTIN * T AYLOR * M ARTIN * M ARTIN * 30 W ALTON * W ALTON * B ROWARD * W AKULLA * B ROWARD * W ALTON * 31 B ROWARD * B ROWARD * W ALTON * W ALTON * W ALTON * B ROWARD *

* 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 siteswhere 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 mostthreatened region is the Gulf Peninsula (23.5 percent of its seagrasses scarred); it has extensive scarring relative to the moderate acreage of seagrassesthere. 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 M ONROE 

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

T OTAL 

### 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. P ANHANDLE 48,170 9,970 2,090 200 2,290 12,260 2. B IG B END 826,770 58,630 6,180 540 6,720 65,350 3. G ULF P ENINSULA 110,260 16,140 21,330 4,580 25,910 42,050 4. A TLANTIC P ENINSULA 69,360 250 3,030 490 3,520 3,770 5. S OUTH F LORIDA 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 inthe 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 extentof scarring was unexpected because of these counties’ lower population densities. However, the large amount of light scarring may have partiallybeen 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 inLee 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 GulfPeninsula 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 havesubstantial 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 FloridaKeys 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. Thisarea, 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 andgrounding scars at others. Some formerly vegetated areas were covered by displaced sedimentfrom 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 inTables 8 and 9 (Kruer 1994). These sites were evaluated for probable causes of scarring based onobserved 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 ClassIII 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 areacontains 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. Unmarkedchannels 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 linearfeet of bulkhead docks along canals in a residential subdivision. Scarring of seagrasses in the Florida Keys hasoccurred for some time—probably since combustion engines (outboard and inboard) were installed in boats. However, the problem of seagrassscarring has become acute because of the increasing residential population; the increasing popularity of boating, fishing, diving, and otherwater 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, shipgroundings, 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, ifMonroe 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? Oneimportant correlation exists with population density, as reflected in vessel registrations for each ofthe 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) moreTable 8. 

### Moderately scarred sites—Marquesas Keys to Snipe Key (1992–93). Adapted from Kruer (1994).

Site # Adjacent Key Probable Suggested Comments Cause 1 Management 2

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 Cause 1 Management 2

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, notonly is the population increasing, but the percentage of the population that owns boats is alsoincreasing. 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, only6.4 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 registeredin 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, MonroeCounty 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 ispredominantly 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 andCharlotte 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 Watercraft Rank Craft Craft

B AY 13,212 89.9 1,488 14,700 15 B REVARD 25,763 93.8 1,716 27,479 7 B ROWARD 39,930 93.7 2,682 42,612 3 C HARLOTTE 14,004 93.7 947 14,951 14 C ITRUS 11,445 91.7 1,039 12,484 19 C OLLIER 13,791 92.2 1,171 14,962 13 DADE 44,542 95.2 2,231 46,773 1 D IXIE 1,544 77.0 461 2,005 30 E SCAMBIA 15,297 96.6 537 15,834 11 F RANKLIN 1,424 57.7 1,045 2,469 27 G ULF 1,866 86.8 284 2,150 29 H ERNANDO 5,293 96.1 212 5,505 23 H ILLSBOROUGH 35,126 97.3 973 36,099 4 I NDIAN R IVER 7,796 94.1 492 8,288 21 J EFFERSON 669 96.3 26 695 31 L EE 29,409 93.6 2,007 31,416 5 L EVY 2,162 86.1 348 2,510 26 M ANATEE 12,865 94.5 752 13,617 17 M ARTIN 12,041 94.0 767 12,808 18 M ONROE 16,152 80.1 4,011 20,163 8 O KALOOSA 13,059 94.3 795 13,854 16 P

ALM B EACH 29,862 96.6 1,067 30,929 6 P

ASCO 14,800 96.6 528 15,328 12 P INELLAS 41,317 94.8 2,279 43,596 2 S ANTA R OSA 7,377 95.4 359 7,736 22 S ARASOTA 16,272 95.0 848 17,120 10 S T. L UCIE 8,839 94.2 543 9,382 20 T

AYLOR 2,399 91.0 237 2,636 25 V

OLUSIA 18,286 95.4 876 19,162 9 W

AKULLA 3,221 86.4 509 3,730 24 W

ALTON 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. P ANHANDLE 59,156 54,525 92.2 4 4
2. B IG B END 44,893 41,533 92.5 5 3
3. G ULF P ENINSULA 156,799 148,993 95.0 1 1
4. A TLANTIC P ENINSULA 108,048 102,587 94.9 3 2
5. S OUTH F LORIDA 124,510 114,415 91.9 2 5
T OTAL 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 aspleasure 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. TheGulf 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 poorlymarked 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 shallowseagrass 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 ofwhat seagrasses are and the benefits they provide, accept as the behavioral norm localboating 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 ofvessels 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 properuse 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 thelocation 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 oncharts, 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 theedges 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. Oftenthese illegal markers indicate where prop-dredging has deepened shallow areas so small boats can get between deeper areas. Boaters in larger vesselsmay attempt to use such markers and unexpectedly pass through water too shallow for their boats. (2) Coastal property is popular because itallows 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. Manydredged 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 depthat 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 areasare 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 thosecounties 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 inthat 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 apparentextent 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 sensemust be used in determining where state management monies are spent. Basing decisions on both the extent of M/S scarring and on an SIvalue 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 scarringof 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), thatcan 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 onlylight 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 makeall boaters—tourists and residents alike—understand the sensitive nature of Florida’s shallow seagrass communities. Florida, with its millions ofvisitors 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; throughpublic-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 shouldemphasize 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 agenciesneed 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—thatlong-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. Thisapproach could be used to communicate seagrassprotection needs to seasonal residents and touristsat 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 locationsand 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 thesame 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 EvergladesNational 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 effectivechannel-marker system are negated if illegal markers and prop-dredged channels are allowed to proliferate.

3. Enforcement Voluntary compliance has not proven effective inthe 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 ofunsafe 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 andMichael’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. Scarringof 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 andreckless damage (e.g., Reckless or careless operation of a vessel. F.S. 327.3; “Duty of the Board ofTrustees 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...”). TheFlorida Administrative Code, Chapter 18-14 discusses fines for damaging state lands. 4. Limited-Motoring Zones Programs initiated by the FDEP, the U.S. Fish andWildlife 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 inthe 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 concernareas 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 33used to monitor the amount of scarring in the preserve (Cockroach Bay Seagrass Task Force 1992). Despite these steps, however, initial reports oftheir 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 hasnot worked, and total closure has been implemented to alleviate scarring. Managers are looking into further measures to reduce scarring losses, such asproactive 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 changesin 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 andJohn 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 thoseattempting 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-termcommitment, 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. Withthe 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 protectFlorida’s marine resources. Although the data presented in this report are of a broad nature, the report provides a basis for further and more refined management of areas subject to an increase in seagrass-resource use.

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. Hillsborough Community College. Tampa, FL. 

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### , L. 1987. Seagrass ecology along the coasts of Alabama, Louisiana, and Mississippi. Pp. 11–24 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.



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### , M.R. 1971 . A study of the effects of a commercial hydraulic clam dredge on benthic communities in estuarine areas. Fl. Dept. Nat. Res. Tech. Ser. 64. St. Petersburg, FL. 51 p.



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### , H. 1982. Sediment suspension andresuspension from small craft induced turbulence: project summary. Chesapeake Bay Program. EPA-600/S3-82-084. U.S. Env. Prot. Agency. Annapolis, MD.



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### . 1985.Assessment and trends of Florida’s marine fisheries habitat: an integration of aerial photography and thematic mapper imagery. Pp. 130–138 in Anonymous (ed.), Proceedings of Machine Processing of Remotely Sensed Data with Special Emphasis on Quantifying Global Process: Models, Sensor Systems, and Analytical Methods. Lab. Appl. Remote Sensing, Purdue Univ., West Lafayette, IN.

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. 1991. Responses of Thalassia testudinum to in situ light reduction. Pp. 77–86 in Kenworthy, W.J. and D. Haunert (eds.), The capability of water quality criteria, standards and monitoring programs toprotect seagrasses from deteriorating water transparency. Results and recommendations of a work

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### , J.G. 1992. Disturbance, dispersal,and patch insularity in a marine benthic assemblage: influence of a mobile habitat on seagrasses and associated fauna. Ph.D. Dissert. Florida State Univ., Tallahassee, FL. 183 p.



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### . 1985. Seagrass meadows of Tampa Bay - a review. Pp. 210–246 in Treat, S.-A. F., J.L. Simon, R.R. Lewis, III, and R.L. Whitman, Jr. (eds.), Proceedings Tampa Bay Area Scientific Information Symposium. Florida Sea Grant College Rep. 65. Gainesville, FL.



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### , R.J. 1987. Historic trends of human 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.



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### , 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.



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### , 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.



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## 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 staffdetermined 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. Usingthis land coverage, digitization effort was minimized without substantially compromising theintegrity 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 attributeswere changed. A second iteration of this qualityassurance process was performed to ensure thecompleteness 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 wereremoved, and where required, the county boundaries were extended offshore to enclose the datajust 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 meetour 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 themost 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 andremote-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 correctingexisting 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 acreageof 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*

B ENDGRASS Citrus, Hernando, Jefferson, 1983 1:40,000 Minerals Management Service Levy, Pasco, Pinellas, Taylor (MMS)

C HARGRASS Charlotte, Collier, Lee, 1982, 1987 1:24,000 Florida Dept. of Transportation, Manatee, Sarasota Florida Dept. of Environmental Protection, Mangrove Systems, Inc., FMRI

IRL GRASS Brevard, Broward, Indian 1992 1:24,000 St. Johns River Water River, Martin, St. Lucie, Management District Volusia

P

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

P

ANGRASS Bay, Escambia, Franklin, 1982–1985 1:24,000 FMRI Gulf, Okaloosa, Santa Rosa, Wakulla, Walton

S FGRASS Dade, Monroe 1982–1986 1:40,000 Marszalek, Dade County, MMS, FMRI

T BAYGRASS 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 theramifications of this phenomenon, a comprehensive assessment of the potential overestimation of scarring was conducted, and suspect areas wereidentified. 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 describesthe 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 decreasedthe 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 highlevel 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 affectedthe 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 anddata from the aerial surveys. For example, seagrass-distribution data used in Charlotte Harbordate 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 theassessment in the Florida Keys was accepted without secondary evaluation because the survey wasdone 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 obviouslypresent 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 ChartsFigures 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 countiesEscambiaSanta RosaOkaloosa5 0 5 10KILOMETERS5 0 5 10MILESStateCountyCountyStateStateCountyAlabamaGulfofMexicoPensacola BayChoctawhatchee Bay

P erdido B ayScale 1:500,000GulfofMexicoAtlanticOceanAlabama GeorgiaENWS



### Figure B1.LandNonseagrass Waters“Nonscarred”SeagrassLight ScarringModerate ScarringSevere ScarringSeagrass OutsideCounties of InterestPropeller Scars OutsideCounties of InterestWaltonBayGulf5 0 5 10KILOMETERS5 0 5 10MILESSCALE 1:200,000StateCountyCountyStateStateCountyGulfofMexicoChoctawhatchee BaySt. AndrewBaySt. JosephBayScale 1:500,000GulfofMexicoAtlanticOceanAlabama GeorgiaENWS



### Figure B2.LandNonseagrass Waters“Nonscarred”SeagrassLight ScarringModerate ScarringSevere ScarringSeagrass OutsideCounties of InterestPropeller Scars OutsideCounties of InterestFranklinWakulla Jefferson5 0 5 10KILOMETERS5 0 5 10MILESSCALE 1:200,000Apalachicola BayApalachee BayStateCountyCountyStateStateCountyGulf ofMexicoScale 1:500,000GulfofMexicoAtlanticOceanAlabama GeorgiaENWS



### 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 R
iver

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 R
iver

Lake Okeechobee Indian

R iver 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 B a n a n a

River Mosquito

L a g

o o n L a g

o o n

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