Seagrasses are considered “keystone” species because of the important habitat-creating role they play in the estuary (Dawes et al. 2004).

Seagrasses:

• Improve water quality by stabilizing sediments, filtering nutrient pollution, storing carbon, and reducing wave action and coastal erosion.
• Serve as an important food source for many aquatic organisms including the West Indian Manatee and the Green Sea Turtle.
• Remove carbon dioxide from the water column and may buffer waters from ocean acidification.
• Seagrass meadows are a recognized ‘blue carbon’ feature of estuaries — an acre of seagrass offsets the carbon footprint of the average car.
• Nearly 80% of commercially and recreationally important fish and shellfish utilize seagrass habitat during their life cycle.

Human development, with the resulting impacts of increasing nutrients and turbidity in coastal waters, is a threat to seagrass beds. Propeller scarring continues to affect seagrass beds throughout the region; beds in Pine Island Sound and Matlacha Pass in Lee County have experienced the most severe damage. The following factors negatively affect the distribution and health of seagrass beds in the Charlotte Harbor region:

• Reduced water clarity from sedimentation (suspended sediments)
• Increased nutrient-polluted runoff from land
• Color changes
• Excessive algal growth
• Propeller scarring by boats
• Natural events (hurricanes, red tide, harmful algal blooms, etc.)
• Freshwater runoff from increased frequency and intensity of storms and drainage
• Excessive increase in Phytoplankton from increased nutrient levels, temperatures, and rainfall

Seagrass requires clean water and ample sunlight to grow. Because seagrass thrives in clean and clear water, it is used by agencies and local governments as a way to measure water quality.

Florida had historical declines in seagrass acreage during the 20th century. National Estuary Programs and Water Management Districts collaborate with local governments and industry to improve water clarity and as a result of their efforts seagrass acreage in some estuaries is stable or increasing. This is documented in two ways:

• Mapping changes in seagrass acreage and location over time with aerial photography (spatial coverage). This is valuable for estimating seagrass locations, acres and broad changes over time.
• On-the-ground monitoring of changes in species composition, estimation of bottom cover in a seagrass bed (abundance), and maximum depth in which seagrass can grow due to light availability and water clarity (deep edge). This monitoring works to characterize the density, complexity, and stability of those seagrass meadows.

Seagrass health is indicated by total seagrass cover (acres), density, and species composition. Throughout the Charlotte Harbor and surrounding estuaries, seagrass has experienced significant declines in acreage (coverage) since 2014-2016. The reason for this decline is complex and likely involves several factors. This includes resuspended sediments and nutrient pollution following hurricanes or other events such as red tide and algae blooms, as well as climate change impacts including increased temperatures and rainfall. 2020/2021 data demonstrate modest gains in abundance of common seagrass species Shoal grass, Turtle grass, and Manatee grass, though not full recovery. The CHNEP continues to work with our partners to better understand causes and investigate solutions. (Source: Southwest Florida Water Management District (2014, 2020) and South Florida Water Management District (2014, 2021).