Explanation of Indicator
As a result of human population growth in coastal areas, estuaries are experiencing a deterioration of ambient water quality. This results in oxygen-deficient water, reduced water column transparency, and a decline in living resources.
The habitat requirements of seagrasses are used to characterize water quality because of seagrasses’ widespread distribution, important ecological role, and sensitivity to water quality parameters. Seagrasses are particularly vulnerable to reduced water clarity (transparency), so their distribution (both depth and extent) is a good indicator of this water quality parameter. Seagrasses provide food for waterfowl, manatees, and green sea turtles and are essential habitat for shellfish and finfish. They also affect nutrient cycling, sediment stability, and water turbidity. Declines in seagrasses are being documented worldwide.
Data Characteristics
SOURCE
This information can be obtained by contacting Frank Sargent at the Florida Marine Research Institute, Florida Department of Environmental Protection, 100 Eighth Avenue, S.E., St. Petersburg, Florida 33701-5095, or at (813) 896-8626.
ACQUISITION
The data can be obtained in hard copy format at no cost.
COLLECTION
Because of the expense, seagrass mapping programs are generally completed in two-to five-year cycles by the water management districts, if at all. In most areas, mapping is conducted in five-to ten-year cycles as joint efforts between state and federal agencies.
Seagrass data used by the Florida Marine Research Institute are from the panhandle, Big Bend, Tampa Bay, Lemon Bay, Charlotte Harbor, south Florida, Palm Beach County, Hobe Sound, Indian River Lagoon, and Mosquito Lagoon. Data for the panhandle were interpreted in 1993 by the Florida Department of Environmental Protection (DEP) from 1984-1985 using color aerial photography. Data for the Big Bend were interpreted in 1984 by the U.S. Department of the Interior Mineral Management Service using natural color aerial photography. Tampa Bay data were interpreted in 1992 by the Southwest Florida Water Management District using natural color aerial photography. Lemon Bay data were compiled in 1988 by Mangrove Systems, Inc. using aerial photography and were digitized into ERDAS. Charlotte Harbor to Estero Bay data were compiled by DEP and the Florida Department of Transportation using aerial photography. South Florida data were compiled from several sources at DEP using aerial photography. Palm Beach data were compiled by Palm Beach County using Auto-CAD and ARC/INFO. Hobe Sound data were provided to DEP by the Jupiter Inlet Aquatic Preserve Manager. Indian River Lagoon data were interpreted by the Saint Johns River Water Management District using color infrared aerials. Mosquito Lagoon data were interpreted from 1986 Landsat-TM imagery by the Bionetics Division of Kennedy Space Center and converted from image format to an ARC/INFO coverage by DEP in 1994.
Data Limitations
This indicator is important as a benchmark. As data become available in the future, changes in acreage of seagrass will be seen; this is significant because seagrass can be used to characterize water quality. This is currently the most accurate data available; however, there are some limitations. Seagrass mapping is done via aerial photography so seagrasses at depths below 30 to 45 feet are not counted. Water clarity can impact the accuracy of the aerial photography by affecting the depth to which the detection equipment can penetrate.
Data Analysis
The total acreage of seagrass in the state is approximately 2,658,290 acres. This estimate is derived by adding all of the acreage figures from the various seagrass mapping projects conducted around the state. This figure includes hardbottom and sparse seagrasses in the Florida Keys. This total should be used as a benchmark until future data are available. It should also be noted that this figure may be a slightly conservative estimate, as there are many regions where some species of seagrasses grow in deep water on a seasonal basis over large areas and therefore would not be detected when the area was being mapped.
Recommendation
Currently the data on acreage of seagrass are inconsistently and infrequently collected. The primary reason for this infrequent collection is the expense of gathering the data. Currently, funding for data collection is provided by the water management districts and/or by federal agencies. Collection of the data is done on a regional basis, however these regions do not cover the entire state, and the timing cycle of collection varies among these regions.
It is recommended that the funding for these projects be increased so that coverage can be comprehensive. The Florida Department of Environmental Protection, Florida Marine Research Institute is currently responsible for compiling the data and should continue to compile the data on a yearly basis. The method of collection, aerial photography, is currently the best available method for mapping seagrass acreage, so it remains the recommended method despite the limitations addressed above.