SWFWMD says seagrass stable along Florida's Springs Coast
FDEP photo of manatee grass in Biscayne Bay Aquatic Preserve.
Southwest Florida Water Management District (SWFWMD)
Scientists with the Southwest Florida Water Management District completed the latest round of seagrass mapping along Florida’s Springs Coast. The results of the aerial imagery collected show 586,511 acres of mapped seagrass habitat along the Springs Coast, up slightly from the previous total of 577,920 acres in 2016. The open water nature of the area and the largely undeveloped and expansive coastal wetlands contribute to the region’s stable seagrass habitats.
This Springs Coast region represents one of the largest and most diverse seagrass ecosystems in the country and the District is committed to monitoring the long-term health of these habitats.
To better understand trends in seagrass habitat, the District further subdivided this region into 16 segments. While the region as a whole saw little change in seagrass acreage and one area should a slight decline, several smaller segments experienced significant gains:
• The Anclote Offshore segment saw the greatest increase (25.7%) from 5,156 acres in 2016 to 6,483 acres in 2020.
• Waccasassa Bay east of Cedar Key also saw significant gains in seagrass (17.1%) from 10,934 acres in 2016 to 12,807 acres in 2020.
• The Crystal Bay Inshore segment saw an increase in seagrass (8.4%) from 25,115 acres in 2016 to 27,223 acres in 2020.
• Some segments saw a slight loss in seagrass. Just off the Chassahowitzka River there was a 3.1% decline from 30,086 acres in 2016 to 29,163 acres in 2020.
Along the Springs Coast, seagrasses are often mixed with other organisms like sponges, corals and attached algae. Among the many ecological and economic benefits of these undersea habitats, approximately 70% of the recreationally and commercially important species of fish, crabs, and shrimp in the Gulf of Mexico spend at least a portion of their lives in seagrass meadows. Seagrasses are also a major food source for manatees and sea turtles.
While seagrasses help maintain good water quality, they are also sensitive to increased nutrient pollution and other stressors like red tide and hurricanes. For this reason, the District maps seagrass habitat every four years to “take the pulse” of the Springs Coast estuaries. The results are used to track trends in seagrass and to evaluate ongoing water quality improvement efforts.
Seagrass maps are created by professional photo interpreters using aerial imagery collected specifically for the purpose of mapping seagrasses. Images are collected using state-of-the-art digital cameras mounted on specially outfitted aircraft. Every image must go through a rigorous quality control process before being released to the photo interpreters. Additionally, qualified field crews visit more than a thousand ground truth and accuracy assessment points to ensure the highest quality map product.
Florida Dearment of Environmental Protection (FDEP)
According to the Florida Dearment of Environmental Protection (FDEP), seagrasses are grass-like flowering plants that live completely submerged in marine and estuarine waters throughout the coastal areas of Florida that are most abundant in Florida Bay and from Tarpon Springs northward to Apalachee Bay in the Gulf, which are two of the most extensive seagrass beds in continental North America. Seagrasses occur in protected bays and lagoons and also in deeper waters along the continental shelf in the Gulf of Mexico. The depth at which seagrasses occur is limited by water clarity because most species require high levels of light.
Florida's approximately 2.2 million acres of seagrasses perform many significant functions.
Maintain water clarity by trapping fine sediments and particles with their leaves.
• Stabilize the bottom with their roots and rhizomes.
• Provide shelter for fishes, crustaceans and shellfish.
• Along with the organisms that grow on them, provide food for many marine animals and water birds.
• The canopy of seagrass protects smaller marine animals, including the young of such species as drums, sea bass, snappers and grunts, from larger predators. Some animals, such as manatees, urchins, conches and sea turtles, eat seagrass blades. Other animals derive nutrition from eating algae and small animals that live upon seagrass leaves. Bottlenose dolphins and a variety of wading and diving birds also use seagrass beds as feeding grounds. Seagrass-based detritus formed by the microbial breakdown of leaves and roots is also an important food source.
Florida's Seagrasses
Although approximately 52 species of seagrasses exist worldwide, only seven species are found in Florida's marine waters (see • below). Six of these are widespread in Florida and extend beyond its borders.
• Turtle grass (Thalassia testudinum), the largest of the Florida seagrasses, has deeper root structures than any of the other seagrasses. It has large ribbon-like leaves that are 4 to 12 mm wide and 10 to 35 mm long. This seagrass is temperature limited and does not occur along the northeast Florida coast, but it forms extensive beds in Florida Bay.
• Shoal grass (Halodule wrightii) is an early colonizer of vegetated areas and usually grows in water too shallow for other species except widgeon grass. It is most common in inlets along the east coast.
• Manatee grass (Syringodium filiforme) is easily recognizable because its leaves are cylindrical instead of ribbon-like and flat like many other seagrass species. The thin leaves are up to half a meter long. The northern limit of manatee-grass is the Indian River, near Cape Canaveral. Manatee grass is usually found in mixed seagrass beds or small, dense monospecific patches.
• Widgeon grass (Ruppia maritima) grows in both fresh and salt water and is widely distributed throughout Florida's estuaries in less saline areas, particularly in inlets along the Florida east coast.
Three species of Halophila are found in Florida. These are smaller, more fragile seagrasses. Only limited information about them exists, although surveys are underway to define their ecological roles.
• stargrass (Halophila engelmannii)
• paddle-grass (Halophila decipiens) and
• Johnson's seagrass (Halophila johnsonii). Johnson's seagrass grows only in the Indian River Lagoon south to Biscayne Bay and is listed as a federally threatened species.