Gulf seagrass beds holding their own

Seagrass in the 820 square miles of coastline between the Anclote River and Levy County appears to be holding its own, despite increasing pollution coming from springs and rivers.

A study of the seagrass beds by the Southwest Florida Water Management District shows slightly more than half the seafloor in the area is covered with dense seagrass. The coverage is similar to what the first mapping and survey of the same area found in 1985.

"At least we're finding consistent results. It's encouraging that we're not finding a decrease," said Keith Kolasa, a senior water management district scientist.

In all, the survey found seagrass coverage ranging from dense to patchy on 378,000 acres of Gulf bottom.

The water management district analyzed aerial photographs from the Florida Fish and Wildlife Conservation Commission to determine the extent of seagrass coverage. District scientists also checked sites to determine whether the photos revealed seagrass or algae.

The survey covered a total of 525,000 acres in the Gulf of Mexico from the mouth of the Anclote River north of Tarpon Springs to the mouth of the Withlacoochee River near Ingles and out to 20 miles from shore.

District scientists found dense seagrass over 272,000 acres and sparse seagrass coverage on 87,000 acres. Patchy seagrass covered another 19,000 acres.

The grass covers a total of roughly 1 million acres going 30 miles into the Gulf.

It is the country's second-largest seagrass meadow with only Florida Bay and the Keys larger at 1.5 million acres, Kolasa said.

This is the fourth time the area has been mapped.

The health of seagrass is vital to fisheries and it acts as a nursery for game fish as well as a home for creatures including shrimp, crabs and scallops.

"No seagrass means no shrimp and no scallops," Kolasa said.

The main threat to seagrass comes from pollution, mainly nutrients that promote algae growth. Some algae can cloud the water and keeps sunlight from reaching the grass.

The nutrients also spur the growth of a variety of brown algae that drifts with currents and covers seagrass beds and reefs. More of the brown algae has been showing up off the stretch of coast included in the survey.

Kolasa said increasing amounts of nutrients are flowing out of rivers from Pasco through Citrus counties and being pumped into the Gulf through springs that vent offshore.

Much of the pollution, especially from the Weekiwachee River, comes from fertilizer that runs off lawns in Spring Hill.

This year's survey of the Gulf coast seagrass beds is the first to use digital photography that yields more detail. The water management district picked up $165,000 of the survey cost with the Florida Fish and Wildlife Research Institute kicking in the balance of $130,000.

Surveys will be done every five years starting in 2011.

A similar survey by the water district showed the seagrass in Tampa Bay expanded by about 1,300 acres between 2006 and 2008. Seagrass now covers more than 29,000 acres in Tampa Bay, the most since the 1950s.

That is below the 39,000 acres of seagrass scientists think covered the bay bottom before then.