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 Seagrass Monitoring in the Charlotte Harbor Estuaries

Charlotte Harbor and its adjacent estuaries make up one of the most pristine and productive coastal ecosystems in the state of Florida. To protect these coastal areas for the enjoyment of future generations, the Florida Legislature has designated most of the waters within the greater Charlotte Harbor complex as aquatic preserves which encompass over 160,000 acres of submerged land and water.


One of the goals of the Charlotte Harbor Aquatic Preserve (CHAP) program is to protect and enhance the health and functioning of seagrass habitats within the Charlotte Harbor complex. Seagrasses are an important resource crucial to the maintenance of shallow estuarine environments.

Seagrasses provide:
  • Primary productive food source for the estuarine system.
  • Shelter, spawning and nursery habitat for many aquatic organisms.
  • Reductions in turbidity.
  • Facilitate sediment stability.
  • Aid in nutrient cycling.

Because of the critical habitat and water quality benefits provided by seagrasses, they are often identified as both keystone and indicator species. The predominant seagrass species found in the estuaries of Charlotte Harbor are: shoal-grass (Halodule wrightii), turtle grass (Thalassia testudinum), and manatee grass (Syringodium filiforme) although other species may be locally abundant.

Turtlegrass (Thalassia testudinum) with epiphytic growth


To date, aerial surveys have been the most widely used tool to determine current seagrass locations and changes over time, however, these surveys do not provide information about species type, health, zonation relative to depth, or how these factors are changing with time. Seagrass health, distribution and abundance are largely determined by the amount of light available to the seagrass blades. Water quality variables such as algae, turbidity, suspended solids, color and chlorophyll on the seagrass blades affect the amount of light penetrating through the water column to the seagrass (light attenuation).

In order to better manage seagrass habitats, preliminary seagrass transect monitoring was conducted in northern Charlotte Harbor and Lemon Bay in 1998 by SWFWMD/SWIM, Sheda Ecological Associates and DEP/CHAP field staff using SWFWMD/Sheda protocols. During the same year, additional transects were established in southern Charlotte Harbor, Pine Island Sound, Matlacha Pass and San Carlos Bay by DEP/CHAP and SFWMD Tarpon Bay field staff using the same protocols. Beginning in 1999 all transects throughout these two regions have been monitored annually by DEP/CHAP staff, with assistance from agency and citizen volunteers. Originally, water quality and clarity data was collected at each transect including: secchi, photosynthetically active radiation (PAR), dissolved oxygen, salinity, and temperature. However, since that time, additional monthly water quality monitoring programs have been established that provide more robust data to use in comparative analysis with the seagrass data.

Seagrass transect

The 50 Seagrass Monitoring Sites within the Charlotte Harbor Aquatic Preserves are located with GPS via a shallow draft boat. Observations are made by either using snorkel or SCUBA equipment.

The protocol includes monitoring transects extending from beginning (landward) of seagrass bed out to the (waterward) deep edge of the seagrass bed, each consisting of individually staked stations spaced 10 to 50 meters apart. Transect lengths range from less than 10 meters to over 500 meters and extend to depths of up to 8 feet. Measurements are taken at each station including: species composition, percent coverage, blade length, shoot density, water depth, sediment, and epipyte load. Percent coverage is assessed using a square meter quadrat based upon the Braun-Blanquet coverage class system. All transects are monitored annually, in the fall, however, bi-annual monitoring on some sites is done between July and February to correspond with times of maximum and minimum seagrass abundance.

Current data management of the CHAP Seagrass Transect Monitoring data consists of an Access data base where statistical methods are used to analyze the data. This data is shared with other resource management, research and educational institutions. Long term fixed transect monitoring information through 2009 from both Charlotte Harbor and Estero Bay Aquatic Preserves is compiled into the CHAP Seagrass Monitoring Report which aids in the interpretation of aerial photography and seagrass maps and helps determine resource management needs.

The Charlotte Harbor Aquatic Preserves Seagrass Monitoring Program is always looking for volunteers. Please contact Mindy Brown at the DEP Charlotte Harbor Aquatic Preserves office in Punta Gorda if interested. Mindy's telephone number is (941) 575-5861 or she may be reached by email at Melynda.A.Brown@dep.state.fl.us.

Last updated: April 12, 2013

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