BH-3
Reduce Propeller Scarring of Seagrass and Pursue Seagrass Transplanting
Opportunities at Select Sites
OBJECTIVES: Enhance seagrass recovery by reducing propeller scarring of seagrass; evaluate
effectiveness of seagrass planting techniques; pursue seagrass restoration opportunities at
appropriate sites; and continue boater education.
STATUS:
Ongoing. Action updated to reflect adoption of extensive manatee protection zones that also
protect seagrasses. Action also incorporates prop scarring and seagrass transplanting research
results conducted to date. Strategy revised to focus scope of seagrass transplanting program more
narrowly, and evaluate effectiveness of manatee zones in reducing prop scarring. Targeted
boater education is an important element of this Action.
BACKGROUND:
Substantial progress has been made in implementing actions which may reduce seagrass
scarring.. An extensive network of year-round and seasonal slow speed zones established
primarily for manatee protection also serves to safeguard seagrasses in shallow waters bordering
the bay shoreline – although adequate enforcement of these zones remains a challenge. (see
Actions FW-1 and FW-6) The regulated areas generally encompass waters 6 feet deep or less,
mirroring the average extent of seagrass beds in the bay.
No- motor, or “poll and troll” zones at Weedon Island and sections of Fort De Soto Park also
help protect manatees and seagrasses by restricting the use of internal combustion engines in
shallow waters. No-entry security zones around MacDill Air Force Base and Port Manatee also
coincidentally protect seagrass beds.
Although limited seagrass transplanting has been implemented in several areas around Tampa
Bay, evaluation of successful techniques and monitoring of seagrass transplanting is a need.
Monitoring and Preventing Propeller Scars
Seagrass scarring is a persistent problem. Boaters new to boating, or new to boating in Tampa
Bay, may find themselves suddenly grounded in the bay’s shallows and resort to “propeller
dredging” through grass beds to reach deeper water.
A statewide survey of seagrass scars conducted in 1995 found that 65% of seagrasses within
Hillsborough County, 45% of seagrasses within Manatee County and 42% of seagrasses within
Pinellas County were lightly to severely scarred (Sargent et al. 1995). The 1995 survey
preceded adoption of the slow-speed manatee protection and no-motor zones now in place; slow
speed and no-motor zone regulations have not been evaluated to determine if, and to what extent,
they have reduced scarring or promoted healing of scars.
Initial studies indicated that scarred beds may take 3.6 to 6.4 years to return to normal density, if
no additional damage occurs during that period (Sargent et al. 1995). However, more recent
research conducted by EPC and USF in the Cockroach Bay Aquatic Preserve showed that prop
scars healed rapidly (Thorne et al, 2012). The EPC study, which utilized side-scan sonar, found
that Halodule wrightii (shoal grass) recolonized scarred areas within 6 months. Recovery also
was observed in Thalassia testudinum (turtle grass) beds. Pinellas County officials also reported
success with using “sediment tubes” to facilitate regrowth of Halodule in prop scars, as part of
mitigation for the Belleair Beach Causeway Bridge.
However, more research is needed to determine whether these results can be reliably duplicated
in other scarred areas, with different sediment types and currents that may cause scouring, and
for slower-growing Thalassia or Syringoidum filiforme (manatee grass).
Although the impacts of scars on fish and shellfish have not been well studied, research
conducted in 2002 in both Tampa Bay and Charlotte Harbor showed no significant declines in
species abundance in seagrass beds with up to 50% scarring. (Bell et al. 2002).
Despite these results, the need for safe navigation in shallow waters to prevent scarring in the
first place remains, and should be a continued focus of boater education efforts.
Refining Techniques for Transplanting Seagrasses
Only about 100 acres of the 20,000-acre increase in bay seagrasses since 1990 has resulted from
transplanting efforts – water quality improvements account for the majority of the gains.
Regaining seagrasses naturally through nutrient management should continue to be the primary
focus of restoration efforts.
However, transplanting may be a locally important tool for “jump-starting” restoration where
seagrass recovery is lagging, sudden losses occur (due to a spill or extreme weather event, for
example), or as mitigation for unavoidable impacts.
Several methods of transplanting seagrasses have been employed in Tampa Bay. Early efforts
involving small units of seagrass had poor survival rates, as the newly planted grasses were
easily washed away by tides and currents. More recent projects have had success transplanting
larger clumps or “sods” of seagrass that include the native soil and intact root systems. These
units – measuring about 8 inches by 8 inches –are often able to withstand more turbulent water
conditions until the grass is fully established.
In a multi-year project at MacDill Air Force Base conducted by Tampa Bay Watch and the City
of Tampa, Syringodium filiforme from a natural “donor site” was transplanted to a nearby
location using the sod technique. After two years, seagrass coverage in the transplant area
increased 28-fold. Nearly a decade after the first transplanting at this location, the seagrass cover
has continued to expand. An additional quarter-acre of Syringodium was transplanted in six plots
in 2012 through EPC and Tampa Bay Watch; by late 2015, a 75% increase was observed.
It is difficult to determine whether this recovery, and similar restoration/mitigation projects, is
the result of natural recruitment or transplanting activities.
Seagrass survival is influenced by multiple factors, including water clarity, sediment type,
rainfall, epiphyte coverage, and wave energy. The location and depth at which the plantings
occur may be more important than the technique used. Just like land-based trees and plants
require specific environmental conditions, like hours of direct sunlight or soil type, transplanted
seagrass – regardless of technique - will not survive if the location is not conducive to fostering
seagrass growth.
Mitigation for construction-related impacts typically requires permittees to track and report
survival to the permitting agencies for a limited period only. Long-term monitoring (greater than
3 years) of restoration and mitigation projects is needed to determine the most cost-effective and
successful methods, and to identify appropriate planting strategies.
STRATEGY:
Activities to assess seagrass scar reduction efforts and enhance scar reduction (some
activities can occur simultaneously):
Activity 1
Develop and implement a study to evaluate the effectiveness of no-motor, slow
speed zones and voluntary “seagrass caution areas” in reducing propeller scars.
Identify and prioritize scarring “hot spots” around the bay to reduce repeated
impact.
Responsible parties:
 Develop and conduct evaluation of slow speed zones for reducing
prop scarring: TBEP (lead for Tampa Bay) with Southwest Florida
Seagrass Working Group. Evaluation can be included as a task in
the seagrass chapter for the Tampa Bay Habitat Masterplan Update
 Identify and prioritize scarring ‘hot spots’: TBEP (lead for Tampa
Bay) with Southwest Florida Seagrass Working Group.
Development of a “hot spot map”, possibly using SWFWMD
aerial photographs, will be included as part of the seagrass chapter
in the Habitat Masterplan Update.
 Identify best management techniques to reduce seagrass scarring:
TBEP (lead for Tampa Bay) with Southwest Florida Seagrass
Working Group, as part of the Tampa Bay Habitat Masterplan
Timeframe:
The Habitat Masterplan will be initiated in 2017 and
finalized in 2019
Cost and potential funding sources: $$-$$$ CWA 320 funds
Location: Baywide
Benefit/Performance measure: Identification of ‘best practices’ to
reduce seagrass scarring and ‘hot spots’ of seagrass scarring
Results: Identification of seagrass scarring “hot spots” and effective
techniques to reduce seagrass scarring will direct restoration and
protection efforts more cost effectively
Deliverables:
 Report on best practices to reduce seagrass scarring: TBEP
 Scarring “hot spot” map: TBEP
Activity 2
Continue to maintain effective seagrass scarring reduction practices. Direct new
efforts to seagrass scarring “hot spots.”
Responsible parties: Local and state governments including Pinellas,
Hillsborough and Manatee counties and the Florida Department of
Environmental Protection are currently managing slow speed zones.
Timeframe: Ongoing for current zones. New efforts, if warranted, in ‘hot
spots’ initiated by 2023.
Cost and potential funding sources: $$ per year (local government
resources; FDEP uses boater registration revenues to help support law
enforcement including patrolling slow speed zones).
Location: Baywide
Benefit/Performance measure: Increased protection of seagrass beds
from propeller scarring. Scar reduction in identified ‘hot spots’.
Results: Maintenance and enforcement of effective seagrass scarring
reduction actions.
Deliverables: Report on ongoing and new seagrass scarring reduction
efforts 5 years after the efforts are implemented (TBEP).
Activity 3
Continue to refine and expand boater education programs to more effectively
reach target audiences, which includes new boaters and boaters new to Tampa
Bay. Improve boater education for rental boat operators and customers. Support
and promote the use of digital technologies (including electronic chart displays,
smartphones and other emerging platforms) to provide real-time information to
boaters and alert them when they are entering slow-speed or no-motor zones (see
Action FW-6).
Responsible parties: TBEP lead (through the Manatee Awareness
Coalition), FWC, FDEP (through its aquatic preserves and state
parks)
Timeframe: Ongoing for TBEP education materials. Digital technologies
initiating by 2023.
Cost and potential funding sources:
 TBEP funding via CWA section 320 for Boaters Guides and other
boater education materials ($)
 Bay Mini-Grants supported by Tampa Bay license plate revenues
($)
 Enhancement of digital technologies (product providers)
Location: Baywide
Benefit/Performance measure: Increased protection of seagrass beds
from propeller scarring
Results: Enhanced awareness of boaters regarding importance of seagrass
and seagrass scarring reduction actions
Deliverables:
 Boater education materials/Boaters Guides (TBEP)
 Other education materials (TBEP Bay Mini-Grants)
 Enhanced digital maps and technology (product providers)
Activities to assess seagrass transplanting techniques:
Activity 4
Develop and implement a long-term monitoring program for seagrass
transplanting and mitigation to assess optimal conditions and techniques for
success. Develop a map of areas in Tampa Bay where seagrass transplanting
could assist in jump-starting seagrass recovery.
Responsible parties:
 Monitoring design: TBEP (lead) as an element of the Habitat
Master Plan.
 Monitoring implementation: Local entities currently participating
in the annual seagrass transect monitoring program including
Tampa Bay Watch, FWC, Southwest Florida Seagrass Working
Group members, FDEP, public or private entities conducting
seagrass transplanting for mitigation
 Map of seagrass transplanting optimal sites: TBEP (lead)
Timeframe:
Develop monitoring design by 2019;
Initiate monitoring program within 2 years of design completion;
Evaluate monitoring results after 5 years of implementation
Create map of optimal transplant sites by 2025
Cost and potential funding sources:
Design: TBEP 320 funds ($)
Implementation: no 320 funds; local entities staff time ($$)
Evaluate monitoring results: TBEP 320 funds for staff time ($)
Location: Baywide
Benefit/Performance measure: Increased seagrass transplanting success
Results: Coordinated, comprehensive approach to seagrass transplanting
that employs most effective techniques in locations with greatest
likelihood of success
Deliverables:
 Monitoring design document (TBEP)
 Report on monitoring results after 5 years (TBEP)
 Map of seagrass transplanting optimal sites (TBEP)
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Accomplishments on BH-3
1996-2006
Action Title: Reduce propeller scarring of seagrass and pursue seagrass transplanting
opportunities at select sites
TBEP played a role in the following:
 Actions taken to protect manatees in shallow water also serve to reduce propeller scarring
of seagrass. See Accomplishments for Action FW-1.
 Conducted an assessment of physical impacts to habitats in Tampa Bay. Results of an
aerial survey conducted in 1992 indicated that 35% of the total seagrass area in Tampa
Bay exhibited heavy and moderately heavy damage from prop scars, while more than
40% of the seagrass areas exhibited sparse or no scarring. TBEP Technical Report #0393.
 Assisted local government partners in sponsoring forums and workshops with
recreational boaters to explore “pole and troll” zones in key areas of the bay.
 Funded an analysis of prop scar damage at the Ft Desoto Aquatic Habitat Management
Area in 1992. Results of this analysis were used by Pinellas County to develop ‘go slow’
and combustion engine exclusion areas. TBEP Technical Report #05-94. Results of a 5year assessment indicated that the placement of signs, coupled with full-time, on-water
presence of law enforcement officers reduced the rate of scarring.
 Regularly stocked marinas, boat dealers and tackle shops throughout Tampa Bay with
boating guides and other education materials, including location and extent of shallow
seagrass beds. Surveys completed by Bay-Friendly Boater kit recipients indicate that the
kits provided valuable information that increased their knowledge, especially with regard
to the shallow nature of the bay, and the need for caution when boating in shallow water
to protect seagrasses and manatees.
 Funded an assessment of the status and ecology of Florida Gulf Coast seagrass
communities, including an evaluation of the extent of seagrass scarring in Florida
estuaries. TBEP Technical Report #03-04.
2006-2016
Action Title: Reduce propeller scarring of seagrass and pursue seagrass transplanting
opportunities at select sites
TBEP played a role in the following:
 TBEP and multiple partners were awarded several grants to conduct elements of a
Longshore Bar Restoration Project, designed to mitigate wave energy and create
conditions conducive to seagrass recovery behind the restored bars. Funding sources
include the Hillsborough County Pollution Recovery Trust Fund to examine wave energy
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effects; FDEP to examine historical changes in offshore bars; US Fish and Wildlife
Service to support engineering studies; and in-kind services from USGS, the Tampa Port
Authority, Mote Marine Lab and Coastal Resources Group, Inc. Grants include support
for construction of the experimental longshore bars (Gulf of Mexico Program grant and
PCEF grant) and for seagrass planting (HC Pollution Recovery Trust Fund). Work on
this large project was initiated in early 2005, and concluded in 2013. TBEP Technical
Report #06-13.
Supported experimental plantings of large (8” by 8”) manatee grass sods as part of the
Longshore Bar project. Two years after the plantings, there was a 28x increase in area
covered over that originally planted. Several of the restored sods were expanding at a rate
similar to natural growing manatee grass areas. TBEP Technical Report #01-09.
An extensive network of manatee protection zones in shallow seagrass areas has been
established in Tampa Bay, along with two no-entry refuges (around power plants). These
zones are a combination of federal, state and local designations, but all require boaters to
go slow or pole/troll in shallow waters where manatees feed and rest. These zones were
approved and posted in FY 04, 05 and 06, and have been maintained without alteration
since their initial creation.
TBEP’s Manatee Awareness Committee spearheaded an important project to incorporate
and display manatee and seagrass protection zones in Tampa Bay on electronic marine
charts for recreational boaters. The chart manufacturer Garmin became the first private
sector partner to include the zones in their electronic navigation systems (FY09).
Navionics followed in FY10 by adding the local zones to their popular “Fish N’ Chip”
for chart plotters. Boaters using these units for navigation will see manatee zone
boundaries highlighted as they scroll over portions of Tampa Bay where slow speed
zones have been established.
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