There is one form of vegetation that is flourishing in this drought-torn region: seagrass.
Seagrasses are what most people think about when they consider what’s under the surface of Sarasota Bay. Seagrass beds are a critical element of the marine food chain, providing nutrients and homes for thousands of varieties of plankton, crabs and fish.
And the underwater grasses are starting to flourish – again – after years of declining productivity.
Scientists have found that the number of seagrass beds in the bay system from Venice inlet to the north end of Anna Maria Island have increased by about 28 percent from 2006 to 2008.
The report shows the most intense increase in seagrass bed coverage has occurred in northern Sarasota Bay from Siesta Key north to Anna Maria Sound; that area saw a 32-percent increase.
Upper Sarasota Bay saw an increase in seagrasses of 1,844 acres. The southern portion of Sarasota Bay had an 850-acre increase; Little Sarasota Bay had a 197-acre increase, while Roberts Bay and Blackburn Bay had declines of 25 acres and 79 acres, respectively, according to biologists with the Southwest Florida Water Management District.
SWFWMD conducts aerial surveys of the bays throughout its region and compares the photos with previous shots to determine seagrass coverage.
For comparison, Tampa Bay saw a 5-percent increase in seagrasses. Charlotte Harbor had a 5-percent decrease.
Why the big increase in this region?
Officials with the Sarasota Bay Estuary Program said they had found a direct correlation between a reduction in the amount of treated effluent from sewage treatment plants flowing into the bays and the added seagrass beds.
The City of Sarasota has dramatically curtailed treated effluent discharges into the bay at Whitaker Bayou, resulting in an increase in seagrass beds there. In northern Sarasota Bay near Tidy Island, Manatee County has added treatment processes at the sewerage plant near that area, plus a deep-well injection process for even more treated sewage.
The "beds of gold" for the bay environmental system should mean bigger harvests of fish, crabs and other marine life in the years to come. More important, though, is the indication that the enhanced seagrass beds have reversed the declines in productivity for Sarasota Bay.
There are seven different species of seagrasses in Florida. Sarasota Bay has five of them: Thalassia testudinum (turtle grass), Syringodium filiforme (manatee grass), Halodule wrightii (shoal grass), Ruppia maritima (widgeon grass) and Halophila engelmannii (star grass).
What’s so important about seagrasses?
"Through their complex physical structure, seagrass meadows serve as habitat by providing shelter for both adult and juvenile crabs, shrimp and fish," James Culter, a technical adviser to the estuary program, said.
"Seagrass blades act as a substrate for an entire community of marine organisms, including microalgae, microinvertebrates, protozoa and diatoms," he continued. "Herbivores that graze directly on the seagrass blades include fishes, manatees, sea turtles and sea urchins, while the attached epiphytes provide a valuable food source for a host of other marine life. Dead leaves and epiphytic growth falling to the bay bottom make up the majority of the material in the detrital food web.
"Seagrass leaves slow the water current and promote the deposit of organic and inorganic particles in the water column; their presence also inhibits the resuspension of sediments," Culter continued. "Roots, runners and rhizomes form an interlocking grid that tends to lock in the accumulated sediments and retard erosion of the bay bottom. The physical energy of waves and currents tends to be dissipated by the presence of seagrass leaves, helping to protect adjoining shorelines from erosion. With their photosynthetic ability, seagrasses are a major contributor of dissolved oxygen to the water column."
In Sarasota Bay, seagrasses are threatened by added nitrogen found in treated sewage effluent and in increased levels of contaminants found in stormwater runoff. Pesticides, excess fertilizer, and petroleum products from automobile exhausts run from yards and streets into the bay, polluting the water and destroying seagrass beds.
More seagrasses means more fish, and more fish means more potential catch for creatures that eat the fish, including human beings.
May 16th 2009 - 1:48PM