Shoreline Enhancement for MacDill AFB; Phase II


I.  Summary


MacDill Air Force Base (AFB), Tampa Bay Watch, Inc. and the United States Fish & Wildlife Service (USFWS) are working to continue restoration of the Interbay Peninsula shoreline.  The partnership between MacDill and Tampa Bay Watch to install oyster habitats along the shoreline is a continuation of a community-based restoration project that began in 2003, known as Phase I.  Phase II work will provide protection along 800 linear feet of shoreline.  MacDill AFB is located at the southern tip of the Interbay Peninsula (Figure 1), and receives substantial wave energy from large vessels navigating the channels as well as natural storm-driven waves.    


This community-based enhancement project involves the placement of 1500 Lo-Pro Reef Ball units and 500 linear feet of oyster shell bars along the southeast corner of the Interbay peninsula, at Gadsden Point.  These Lo-Pro reef balls are marine-friendly, hollow, concrete oyster domes that will provide shoreline stabilization for the currently eroding coastline and habitat for marine life.  Sediment accretion landward of the domes will eventually provide the substrate for Spartina alterniflora, or salt marsh and other native coastal vegetation to further stabilize this eroding shoreline.  This area contains large black mangroves, Spartina sp., palms and live oaks that are being destroyed by the pounding waves.  Future enhancement and restoration plans include community-based plantings of the salt marsh along the southeast coastline of MacDill AFB.    


II.  Background


Phase I of this multi-stage project commenced in early 2004 with the installation of 910 Lo-Pro Reef Ball units protecting 800 linear feet of MacDill AFB shoreline.  Along with two 100’ oyster shell bars, the oyster domes protect the southeastern shoreline midway between Catfish and Gadsden Points (Figure 2) from continuous wave action.  Monitoring of this project is currently underway and will continue through the first half of 2006.  Observations thus far have shown excellent sediment accretion behind the domes and bars, a positive sign of shoreline reestablishment.   

The photo on the left identifies the substantial oyster growth after four months on both the domes and the oyster shell bars constructed in Phase I.  Besides helping to stabilize the shoreline, oyster dome communities provide environmental enhancement in the form of hard-bottom habitats for fish and wildlife resources. 


Expansion of hard bottom surfaces will create a greater surface area for settling spat (oyster larvae), and create habitat niches for other benthic organisms.  In addition to wave relief, these domes promote the following community benefits: 


§         The oyster communities improve our local water bodies, as oysters are filter feeders, capable of surviving in a variety of water quality conditions are found throughout the estuarine portion of the Tampa Bay ecosystem.  Oysters can filter up to 37 liters (9.8 gallons) of seawater every hour (Friese, 1973) providing a natural filter, primarily for algae, in the nutrient laden waters of the Bay. 


§         Oyster communities provide diverse food sources or foraging areas for a variety of important fish species, birds and other wildlife species.  The constructed oyster communities provide recreational opportunities related to these species.


§         Initially, the oyster domes provide increased surface area for the attachment of sessile organisms and provide protective habitats for larger invertebrates and fishes.  Oyster communities also help stabilize bottom sediments, which reduces turbidity levels and lowers erosions rates of shoreline areas.


Once the shoreline stabilizes, restoration efforts along this area will include planting native salt marsh grass, or Spartina alterniflora, to further protect the shoreline from constant wave energy.   


Plans for Phase II provide protection of an additional 800 linear feet of shoreline at Gadsden Point.  Figure One illustrates the Hillsborough Channel Cut A, the large vessel access to Tampa Bay that is approximately 2000 yards (approx. 1.25 nautical miles) off Gadsden Point.  According to Port Operations at the Tampa Port Authority, 3,313 vessels utilized this channel from September 2002 to October 2003.  This equates to one large vessel (tugs, barges, cargo or cruise ships) passing by Gadsden Point every 2.6 hours.  These ships cause substantial wave energy; effectively moving sediment along the shorelines of the peninsula, as the short distance from the ship channel does not allow the waves to dissipate. 


III.  CORE Description


The goal of Tampa Bay Watch’s Community Oyster Reef Enhancement (CORE) program is to increase the oyster population in Tampa Bay and at the same time, provide habitats for small organisms, prevent shoreline erosion, improve water quality and promote fish and wildlife habitats.  In addition, this project benefits the Tampa Bay community by promoting environmental awareness and offering hands-on experience in habitat restoration. 


Oyster shell bars will be constructed similar to natural oyster communities found along shoreline areas throughout Tampa Bay.  Fossilized oyster shell from local shell mines provides a hard surface for oyster larvae to settle upon and grow, eventually forming a natural reef.  Mesh bags filled with fossilized shells will be used to create the oyster bar habitats.  Each oyster shell bag is 20 inches long by eight inches in diameter and made of diamond oriented tubular mesh filled entirely with fossilized (oyster) shell.  The design has been used extensively by the South Carolina Department of Natural Resources (SCDNR) to reduce movement of deployed shell for many of their oyster restoration projects.  This type of mesh does not unravel and has not been shown to cause adverse affects to fish and wildlife resources. 


No oyster shell or oyster bags will be placed in seagrass areas or in any areas containing any significant benthic infauna.  Typically, natural oyster beds are located in the tidal flats from +1.5 mean low water (MLW) and lower, which is periodically exposed and limits seagrass growth.  All new oyster bars (and domes) will be constructed landward of MacDill AFB “Do Not Enter/Boater Exclusion Zone” signs posted approximately 100 feet offshore. 


Over the last four years, Tampa Bay Watch has created multiple oyster shell bars at five locations in and around Tampa Bay.  The picture on the right depicts a one layer, two bag wide oyster bar constructed at Palonis Park, a City of Tampa Park on the eastern shore of Old Tampa Bay at the Gandy Bridge.  These shell bars have been successful at both sediment accretion as well as new oyster recruitment. 


Lo-Pro Reef Ball units will be placed to provide wave attenuation to assist with erosion control and to provide habitat for marine life.  The oyster dome units are half-round in shape and are made from marine-friendly concrete (additives are added to the concrete to neutralize the pH, making it compatible to marine life).  The oyster domes are 24” in diameter and 18” tall and weigh about 75 lbs.    These reef balls are well suited for the establishment of oysters that are common throughout Tampa Bay and along MacDill AFB shoreline.  Placing the Lo-Pro’s in approximately two feet of water would allow the units to be mostly exposed during low tide and totally submerged at high tide; conditions which are optimum for oysters in Tampa Bay.  Reef ball units will create habitat by encouraging oysters and other filter feeders to attach. 


The submerged oyster domes are covered with large holes on the perimeter with a large opening in the middle, extending to the top of the dome.  These holes enable waves to penetrate the unit and allow an easy flow of wave energy.  Water enters the holes on the sides of the reef balls and then is dispelled out the top.  The diagram illustrates how the water exits out the top of each unit.  This movement of water will keep the unit stable and immobile.  The waves, in essence, will not reflect backwards; but in all directions, more effectively reducing the waves. 



IV.  MacDill AFB Phase II Description


Oyster Shell Bars

Tampa Bay Watch staff, MacDill AFB staff and volunteers will construct 500 linear feet of oyster shell bars along the southeastern corner of MacDill AFB in the following manner:



Pile of old cable    and old fence post 

Oyster shell bars created at the southeast point of the Interbay Peninsula will assist with protecting 800 linear feet of salt marsh and mangrove shoreline.  Erosion and tidal influence has affected the cluster of mangroves at the inlet opening and warrants shell bag construction.  A 200 foot oyster shell bar will be constructed, beginning at the southeast point and extend 200 feet east-northeast, mimicking the natural shape of the shoreline (Figure 3). 


§         The remaining 300 feet of oyster shell bars will consist of six 50’ bars constructed landward of the Reef Ball communities.  Two of these shell bars will encompass existing marine debris—an old fence post and a tangle of old cable—in their design and construction (Figures 3 and 4).    


§         All oyster shell bars will be built in shallow water using oyster bags placed approximately 15’ from the shoreline.  Figure five (5) illustrates each oyster bar measuring 5’ wide and 0.66’ tall (three rows of bags = 5’ width).  Typically, natural oyster beds are located in the tidal flats from +1.5 mean low water (MLW) and lower.  All new oyster bars (and domes) will be constructed landward of MacDill AFB “Do Not Enter/Boater Exclusion Zone” signs posted approximately 100 feet offshore (Figure 7). 


Reef Ball Units

A total of 1500 Lo-Pro Reef Ball units will help protect 800’ of shoreline at the southeast corner (Gadsden Point) of the Interbay Peninsula.  This particular corner of the AFB receives constant wave energy from the two ship channels (Hillsborough Cuts A and C, Figure 1) that run parallel to the east and south coastline of the peninsula.  


The proposed plan is to purchase the oyster domes from Reef Innovations in Sarasota and have them delivered the day of each event.  When the domes are complete, they will be placed by community volunteers along the shoreline in the following manner.  The project will be constructed where the water is typically 1.5’ to 2’ deep at mean high water (MHW). 


§         The reef balls will be placed on the sandy bottom along the most southeast shoreline of the Interbay Peninsula.  There are no signs of seagrass beds or intertidal vegetation or other significant natural resources in the project area.


§         Figure four (4) illustrates how the oyster domes will be placed along the shoreline.  Seven serpentine lines of domes will be installed, beginning at the stand of mangroves at the southern tip, following the coastline 800 feet north. 


§         Each 150’ line consists of 195 domes per line and will protect 120’ of shoreline.  Two and three rows of Lo-Pro Reef Balls™ touching at the base will measure 4’ and 6’ wide (1 row = 2’) and 1.5’ high (Figure 6).


§         Two of the serpentine lines (lines 4 and 6, Figures 7,8) will be constructed differently.  This area of the shoreline has two mature Quercus virginiana (live oak tree) which have exposed roots due to erosion.  Extra wave attenuation protection for this area will prevent additional erosion and hopefully allow for the survival of these trees.  A double row of domes (approx. 60 per line) will ‘enclose’ the bend of the serpentine line. 


§         Approximately twenty-five oyster units will be randomly placed near the vicinity of lines 4 and 6.  These domes will provide additional habitat for marine life, as well as substrate for oyster recruitment.


§         Oyster shell bags will be placed in the ‘interior’ of the enclosure for two reasons; to help stabilize the landward domes, and to provide habitat for oyster and marine wildlife.  The estimated number of shell bags needed for the two ‘interiors’ is approximately 970 bags (Figure 8).  


§         Each serpentine line will overlap the next by 20’ and will feature a 10’ gap to allow marine animal species to access shallower and calmer waters (Figures 4 and 6).   This extended overlap will prevent sediments from washing out.   The oyster shell reefs landward of these reinforced dome lines will provide additional defense from wave action and allow for sediment accretion.   


V.  Materials:


§         1500 Lo-Pro Reef Balls™

§         49.1 tons of cleaned, local, fossilized shell

§         to assemble 2975 shell bags


VI.  Task Description: 


The project is designed to be accomplished in the following manner: 


Task 1.  Permitting and Interagency Coordination


Permit applications will be submitted to the Tampa Port Authority from MacDill AFB.  The Environmental Protection Commission of Hillsborough County also reviews the application.  Permit application will also be prepared by MacDill AFB and submitted to the Florida Department of Environmental Protection and the US Army Corps of Engineers. 


Task 2.  Schedule Project Dates


Based upon receipt of the appropriate permits, the project dates will be scheduled.  The project is anticipated to commence in the spring of 2005 and be completed by the end of 2007.


Task 3.  Arrival of Materials / Area Preparation


The oyster reef material of choice is clean, washed 3” fossilized oyster shell that is mined locally and can be delivered to each oyster shell bagging site the day prior to the event.   Tampa Bay Watch will coordinate with MacDill AFB for delivery to an appropriate area.


Marine-friendly Lo-Pro Reef Ball units will be constructed by Reef Innovations of Sarasota and Tampa Bay Watch staff and then delivered to the site at MacDill AFB the day of the event.


Task 4.  Event Coordination 


Volunteers will shovel the shell into pre-cut PVC pipe “sleeved” with the mesh.  The PVC form is removed; creating an oyster shell bag that is tied at both ends.  These “bags” are then loaded onto an ATV and delivered to the shoreline.  Staff from Tampa Bay Watch and MacDill AFB will be on-site to ensure proper placement of the oyster shell, and to minimize human impact on shoreline vegetation. 


Lo-Pro Reef Ball units will be unloaded from the delivery vehicles and carried to the water by volunteers, Tampa Bay Watch and MacDill AFB staff then positioned into place.


Task 5.  Follow-up Monitoring and Reporting


Tampa Bay Watch will monitor the newly deployed oyster reef units and constructed oyster shell reefs every six months for two years for the following parameters:  oyster shell migration, new oyster colonization, changes in erosion patterns, sediment accretion and wildlife usage of the new oyster communities.  Tampa Bay Watch and MacDill AFB will publish the results of the effort and distribute to program participants, permitting agencies, program sponsors and environmental organizations. 


VII.  Timeline


MacDill AFB and Tampa Bay Watch will begin the process of applying for permits in the fall of 2004.  Volunteer coordination and equipment accumulation will take place two months prior to each event.  The construction of these shallow water oyster bars and dome deployment will be scheduled between February and May 2005 to coincide with natural oyster recruitment in Tampa Bay.  The newly created oyster communities will be monitored every six months for a two-year period.  A final report will be prepared at the end of the two-year period. 


Figure 1







Hillsborough Channel Cut C





Hillsborough Channel Cut A
















Figure 2




MacDill AFB


Catfish Point