Seagrass Restoration a Multi-Pronged Effort

While many questions remain about the best way to restore seagrasses beds in Tampa Bay, scientists all agree that maintaining water quality is the single most important concern.

A major step toward that goal was achieved in September when the Tampa Bay Estuary Program’s Nitrogen Management Consortium signed off on a landmark agreement to limit nitrogen pollution in Tampa Bay. The agreement, still pending final approval by regulators and local authorities, spells out how much nitrogen can enter Tampa Bay through 2012.

Photo: Roger Johansson

Working with both professionals and volunteers through Tampa Bay Watch, seagrass plugs were transplanted from a site near Gandy Bridge to protected waters off MacDill Air Force Base.

To achieve consensus, most participants had to give up some previously permitted, but unused capacity. For example, communities that hold permits to discharge more treated wastewater than they currently are must “hold the line” at current levels unless they can prove they have lowered nitrogen pollution elsewhere. Participating private sector partners must meet the same restrictions.

Nitrogen reductions already have resulted in more than 6,000 acres of new seagrasses, with the bay now boasting more seagrass than has been seen since the benchmark 1950s. Nearly all of those restored areas were achieved through natural recolonization, although ongoing restoration initiatives in some parts of the bay are showing promising results.

Research Underway at MacDill
Efforts to restore seagrasses in the protected waters off MacDill Air Force Base are focused primarily on testing scientific concepts not restoring large areas of seagrasses, notes Walt Avery, a senior environmental scientist with the City of Tampa’s Bay Study Group. Two studies underway now are looking at how seagrasses affect longshore bars and how well compressed succession works.

Manatee grass was transplanted from a donor site near the Gandy Bridge to the MacDill property in Summer 2006 using a hand plugger that kept seagrasses attached to the sediments they grow in to minimize transplant shock. The seagrasses have visibly expanded over that time, but it’s still too early to conclude their impact on longshore bars. “What we want to see is their impact on the accumulation of sediments and noticeable changes in the longshore bars due to physical force of waves and tides,” said Roger Johansson, chief biologist with the Bay Study Group.

The concept of compressed succession hypothesizes that transplanting other species into meadows that are primarily Shoal grass will result in beds of more advanced species more quickly than would occur without intervention.

Shoal grass, typically the first seagrass to recolonize an area once water quality and other conditions improve, is also the first to die when those conditions change, explains Robin Lewis, president of Coastal Resources Group and a long-time bay advocate. Most of the new seagrasses in Tampa Bay are Shoal grass, which may be lost when normal rainfall patterns resume and higher levels of nutrients are washed into the bay with stormwater. Turtle and Manatee grass take longer to recolonize an area but are more tolerant of less-than-perfect conditions once they are growing.

Mitigation is Focus at Port Manatee
While the work at MacDill focuses on scientific concepts, similar work underway at Port Manatee is mitigating damage to seagrass beds caused by dredging for the port’s new turning basin and berth. The original mitigation effort, which began in 2000 was controversial but ultimately accepted by the state Department of Environmental Regulation – with the caveat that Turtle grass be planted in Shoal grass beds.

“Even with compressed succession, it’s a long process,” notes Ray Dennis, senior project manager at WilsonMiller who has been involved with the Port Manatee project practically since the beginning. “We had a cumulative survival rate of 73.31% two years after it was transplanted, which is pretty darn good for Turtle grass.”

Two innovative techniques were deployed on two sites totaling 4.95 acres. First was a pneumatic plugger that uses compressed air to release the vacuum created when a plug is pulled from the sea bottom. Then, a clustering system that placed plugs in a hexagon shape nearly quadrupled the area covered when compared with planting on standard 3-foot centers.

“We could have packed them in a little tighter but the trick is to shoot the curve and shorten the success period, without using too many plugs that cost extra money and take away from a finite amount of donor material,” Dennis said.

Restoring Scars with Sediment Tubes
The most recent comprehensive assessment of seagrass beds completed in 1995 indicates that more than 173,000 acres of seagrasses in Florida were scarred. Thirteen years later, with more boats than ever on the water, the scars have almost certainly become worse even if they haven’t been measured.

And left untreated, deep scars in seagrass beds allow increased wave action so they become even wider and deeper, notes Jeff Beggins, CEO of Seagrass Recovery Inc., which has completed more than 150 recovery projects around the world. Sediment tubes, designed to break down in about a year, can bring the surface up to grade so that healthy grasses can spread into it or plugs can be transplanted at grade once the tubes disintegrate.

Working with The Ocean Foundation and funded through Absolut Vodka, Seagrass Recovery launched the Restore-A-Scar program in the Florida Keys last summer. Plans are underway but not finalized for the partnership to launch a second site in Tampa Bay with funding from public and private donors pegged at $10 per square foot.

“Cockroach Bay and other areas in Florida are in dire need of massive restoration efforts,” Beggins said. “Restoring seagrasses is not a question of something we should do or not, it’s something we must do.”

EDITOR’S NOTE: We’ve chosen to use common names rather than Latin names for seagrasses, even in direct quotes, to make the average reader more comfortable. As referred to in this article, Shoal grass is Halodule wrightii, Manatee grass is Syringodium filiforme and Turtle grass is Thalassia testudinum.