TBEP Oyster Habitat Suitability Index (HSI)

Eastern oysters (Crassostrea virginica) are ecosystem engineers and the reefs they build provide critical ecosystem services to coastal communities. Oyster reefs provide a safe haven for juvenile fish and are food source for a wide variety of invertebrates, fish, and birds. Oysters also increase water clarity and improve light availability for seagrass. Humans harvest oysters for food and mine their shell for road base, cement, and similar uses. Living reefs in the water protect the shoreline, and nearby urban development, from erosion. Oyster habitat has declined by 85% or greater throughout the world (Beck et al. 2011), including in North America and in Florida’s estuaries. Prominent causes for the decline of oysters in Florida include a direct loss of habitat due to dredge and fill construction, altered freshwater flows, and loss of adequate substrate due to dredging, shell mining, or excess sedimentation. Oysters were once abundant in Tampa Bay, and numerous middens scattered on the shorelines of Tampa Bay are proof of the importance of this shellfish (and other estuarine resources) to indigenous populations. Tampa Bay had a robust oyster industry through the mid-1900s in locations such as Papys Bayou, the Little Manatee River, and portions of Old Tampa Bay.

Habitat Suitability Index

Oyster Restoration in Tampa Bay

The widespread loss of oyster reefs and the many ecosystem services they provide has led to the implementation of a series of oyster restoration projects (by Tampa Bay Watch, Manatee County, and others in Tampa Bay) beginning in the early 2000s. Additionally, multiple coastal habitat restoration projects that have not had oysters as a primary focus have seen significant production of reefs or on red mangrove (Rhizophora mangle) prop roots. More recently, oyster restoration in nearshore areas has been recognized as a potentially important component in the creation of “living shorelines”, an attempt to create resilience along generally urbanized shores by using more natural approaches to reduce erosion or mitigate other issues associated with sea level rise and climate change while providing a variety of ecosystem services. The TBEP has established a target of 50 acres of oyster reef restoration in the next 10 years within its 2020 Habitat Master Plan Update.

Why a Habitat Suitability Index?

This 50-acre oyster restoration target is about three times greater than the amount of oyster restoration that has occurred in Tampa Bay in the past 20 years. Future work will need to be conducted in a fairly strategic manner, identifying locations within the bay that have the best chance for restoration. Environmental factors including sediment, salinity, and depth help to identify appropriate locations for reef placement, while information regarding existing seagrass beds and channels identify areas that are less suitable. This HSI combines these multiple data layers that are recognized as important factors to enhance or preclude oyster restoration success and creates a mapped scoring system that indicates more probable locations.

How Was the HSI Made?

The data, within a series of Geographic Information System (GIS) layers, was scored for suitability on a scale of 1 to 3, with 3 being most suitable. This information was compiled in a 10x10 meter grid system throughout the bay and into tributaries such as the Hillsborough and Manatee Rivers. Scoring was calculated using this formula:

Model Score = bathymetry score + isohaline score + seagrass score + navigation channels score + sediment score

Higher scores are considered more appropriate for oyster restoration. While estimates have been made for potential oyster restoration for each segment of Tampa Bay, the information will generally be more useful on a smaller scale, focusing on specific areas to determine their suitability for oyster restoration.

Suitability Map

This interactive map provides an opportunity to examine the overall model results as well as individual layers. The information will be helpful as part of conducting full site assessments during the oyster restoration planning and permitting processes.

Many volunteer organizations are helping to restore oyster reefs, such as this one, in Manatee County's Robinson Preserve. Credit: Solutions To Avoid Red Tide

Suitability Summary

This map identifies areas throughout Tampa Bay that might be good for oyster restoration. There are 17,769 acres in Tampa Bay that received scores of 15 (perfect) and 14 in the model. Given that the 2020 Habitat Master Plan established a target of 50 acres over the next 10 years and 300 acres before 2050, there appears to be more than sufficient ‘opportunity space’ for placement of oyster restoration projects.

Where should we be focusing efforts according to the model? The information gives us a better focus on saline portions of tributaries and shorelines near the mouths of those tributaries, such as the Manatee, Little Manatee, Alafia, and Hillsborough Rivers, Channel A, and Allen’s Creek. Upper embayments, such as Clam, Long & Cross Bayous, Riviera Bay, and McKay Bay should also be examined. In addition, numerous dead-end canals were classified as optimal for restoration, which could be done as part of the ongoing living shoreline work in the region.

The upper reaches of some tributaries (for example, the Braden, Alafia, and Palm Rivers) lack different data layers that are needed to be incorporated into the model. This does not mean that these areas should be excluded from consideration for restoration, and data available for the nearest tributary reaches should provide guidance as to probability for oyster success. However, additional work should be conducted in these areas to verify suitability for restoration potential.

Factor Metric Data Source Reference Model Scoring
Seagrass Habitat Occurrence of seagrass during bi-annual SWFWMD aerial surveys SWFWMD Seagrass Data TBEP Comprehensive Conservation and Management Plan, 2017
  • Most suitable: No SAV observed
  • Less suitable: SAV observed in 1 or 2 years
  • Least suitable: SAV observed > 2 years
Boat Channels Distance to boat channel ESRI Waterways Florida (accessed 2020/08/28) Wall et al., 2005
  • Most suitable: Outside a 75-foot buffer
  • Less suitable: Inside buffer
  • Omitted: Within channel
Depth Estimated at Mean Low Water (MLW) USGS Topobathy Data Boswell et al., 2012: CHNEP Oyster Habitat Restoration Plan
  • Most suitable: Less than 0.9 m
  • Less suitable: 0.9-1.8 m
  • Least suitable: > 1.8 m
Salinity Measure in Practical Salinity Units (psu) Environmental Protection Commission of Hillsborough County Kaufman, 2017
  • Most suitable: > 60th percentile for mean salinity > 2.5 psu
  • Less suitable: 30-60th percentile for mean salinity > 2.5 psu
  • Least suitable: < 30th percentile for mean salinity > 2.5 psu
Silt-Clay Percent silt-clay Environmental Protection Commission of Hillsborough County Kaufman, 2017
  • Most suitable: < 17.5% silt-clay
  • Less suitable: 17.5-23% silt-clay
  • Least suitable: > 23% silt-clay

Project Contacts


Barnes, T.K., A.K. Volety, K. Chartier, F.J. Mazzotti and L. Pearlstine. 2007. A habitat suitability index model for the eastern oyster (Crassostrea virginica), a tool for restoration of the Caloosahatchee Estuary, Florida. Journal of Shellfish Research 26:949–959.

Crosby, M.P., C.F. Roberts and P.D. Kenny. 1991. Effects of immersion time and tidal position on in situ growth rates of naturally settled eastern oysters, Crassostrea virginica (Gmelin, 1791). Journal of Shellfish Research 10: 95-103.

Grizzle, R.E., Adams, J.R. and L.J. Walters. 2002. Historical changes in intertidal oyster (Crassostrea virginica) reefs in a Florida lagoon potentially related to boating activities. Journal of Shellfish Research 21:749-756.

Kaufman, K. 2017. Tampa Bay Environmental Restoration Fund Final Report: Hard Bottom Mapping and Characterization for Restoration Planning in Tampa Bay. TBEP Technical Report #03-17. 58 pp.

Kennedy, V.S. and L.P. Sanford. 1999. Characteristics of relatively unexploited beds of the eastern oyster, Crassostrea virginica, and early restoration programs, pp. 25-46. In Luckenbach, M.W., R. Mann and J.A. Wesson (eds.), Oyster Reef Habitat Restoration: A Synopsis and Synthesis of Approaches. Virginia Institute of Marine Science Press, Gloucester Point, VA.

Kennedy, V.S. 1996. The ecological role of the eastern oyster, Crassostrea virginica, with remarks on disease. Journal of Shellfish Research 15:177-183.

Volety, A.K., S.G. Tolley, A.N. Loh and H. Abeels. 2010. Oyster monitoring network for the Caloosahatchee estuary 2007-2010. Final Report submitted to the South Florida Water Management District. 145 pp.

Wall, L.M., L.J. Walters, R.E. Grizzle and P.E. Sacks. 2005. Recreational boating activity and its impact on the recruitment and survival of the oyster Crassostrea virginica on intertidal reefs in Mosquito Lagoon, Florida. Journal of Shellfish Research 24(4):965-973.

Photo Credits