News Press

Caloosahatchee grass recovering

Patches of tape grass in Caloosahatchee are bits of good news

by kevin lollar

klollar@news-press.com

May 29, 2009

http://www.news-press.com/apps/pbcs.dll/article?AID=/20090529/GREEN/905290381&template=printart

Val is back - a good sign for the Caloosahatchee River as Southwest Florida heads into the rainy season.

At the end of 2006, high salinity caused by a long drought wiped out the river's tape grass, an important freshwater plant often called Val, since its scientific name is Vallisneria.

In November 2008, after three months of above-average rainfall, tape grass started sprouting in the river and now is in sparse patches from Beautiful Island to the W.P. Franklin Lock, said Rick Bartleson, a research scientist at the Sanibel-Captiva Conservation Foundation Marine Laboratory.

"Val is an indicator of the health of the estuary," Bartleson said. "In the old days, we had fresh water in the river all year, and we had Val all the way to the Cape Coral Bridge. Now we get fresh water in flashes after rain events.

"Our freshwater supply has been shrinking, and the estuary has been shrinking."

The Caloosahatchee is a tidal river, and its health depends in part on the balance of fresh and salt water - freshwater species such as tape grass grow upstream, while marine species such as oysters and turtle grass grow farther downstream; mobile species move up and down the river as salinity changes.

Many organisms in the river can tolerate short fluctuations in salinity, and under natural conditions, rain events and drought caused brief changes in the river's salinity.

But the balance can get out of whack because the river is now a managed system.

After large rain events such as hurricanes, water levels in Lake Okeechobee rise, and the Army Corps of Engineers releases large amounts of water down the Caloosahatchee; as a consequence, the river can become almost fully fresh.

These releases also carry nutrients from the lake, which, along with nutrients in runoff from along the river, can cause massive macro- and microalgal blooms that can smother seagrasses.

On the other hand, development in the watershed and demand for drinking water have disrupted the natural flow of fresh water into the river, so during droughts, salt water can move far upstream and kill freshwater organisms - tape grass stops growing when salinity reaches 10 parts per thousand and dies at 15.

Vallisneria is an important part of the river's ecosystem: It helps prevent algal blooms by trapping nutrients; it stabilizes the river bottom; it's food for fish, turtles, manatees and birds, and it provides habitat for juvenile fish and invertebrates.

Salinities at Fort Myers, a traditional tape grass area, are still too high for Vallisneria (15.9 ppt), but at Beautiful Island, the salinity is 9.9, and at Franklin Lock, it's 8.5.

Technically, while salinities have dropped upstream from Fort Myers, the South Florida Water Management District classifies conditions in the upper estuary as "poor" because the 30-day average salinity in that part of the river is high.

"Rain has brought fresh water into the upper portion of the river, and salinities have decreased," district spokeswoman Susan Sanders said. "It's good, but it's still not at the ideal levels."

Although Val has made a comeback in the river, it's not thriving as it once did, Bartleson said. In the 1990s, the average length of tape grass blades was 15 inches; now it's 1.5 to 4 inches.

"In Lake Okeechobee, it's 10 feet in 6 feet of water," Bartleson said.

Tape grass isn't the only sign of the times in the Caloosahatchee.

During the drought, many marine fish species moved up the river with the high salinity, including goliath and gag grouper, mangrove snapper, snook, Spanish mackerel, redfish and spotted seatrout, said Dave Westra, owner of Lehr's Economy Tackle in North Fort Myers.

"This year, we didn't see the variety of fish up the river that we saw last year," he said. "Now, I suspect that since we've had some rains in the past couple of weeks, a lot of those species we did get will go. All in all, I think the river is in far better shape than it was three or four years ago."

Oysters, which prefer salinities of 15 to 28 parts per thousand, are an indicator of the Caloosahatchee's health farther downstream, and they're doing fine as they begin their reproductive season, said Aswani Volety, chairman of FGCU's Department of Marine and Ecological Sciences.

"Typically, with dry conditions, salinity is really high, and that creates higher predation and disease in oysters," he said. "But we're getting rain, and the salinities are becoming more brackish. We're seeing the number of living oysters increasing."

Another good sign is that the river's chlorophyll-a levels are low - chlorophyll-a is the green photosynthetic pigment found in plants and algae; low chlorophyll-a levels mean not much algae and, therefore, few nutrients.

Dissolved oxygen levels in the river are good, too.

Not all is well in the Caloosahatchee, however.

"Macroalgae are growing well, especially at the mouth of the river," Bartleson said. "There are just tons of algae growing, but it's not becoming a big problem on the beaches because there are fewer nutrients."