Sea grass research points to changing coastal environment

August 4, 2004

GAINESVILLE, Fla. — Sea grasses — essential to Florida’s marine ecology — are changing near the mouths of rivers on the state’s west coast, and nutrients in runoff from farms, yards and septic tanks may be the cause, according to University of Florida researchers.

“Large-scale losses of sea grass in this area would mean fundamental changes to coastal ecology – comparable to clear-cutting a rain forest,” said Jason Hale, a biologist with UF’s Institute of Food and Agricultural Sciences.

He said sea grasses spend their lives underwater and need a certain amount of light to survive. Around the world, researchers have found that excess nutrients from cities and farms, as well as yards and septic tanks, along coastal rivers leads to decreased water quality and clarity in adjacent estuaries, thereby decreasing the required amount of light sea grasses need to survive.

Loss of sea grass can be detrimental to the coastal environment because the plants serve an important role as habitat and food for many marine species. While manatees and green sea turtles eat sea grass, some species of crabs, fish, and shrimp live in it or eat the algae growing on its blades.

“There are about half a dozen ecological functions that scientists credit to sea grass,” Hale said. “One of them is habitat, a place to hide or live or forage. Another is food for a variety of marine creatures. And, sea grasses help improve water clarity by filtering particles from the water around them.”

In addition to decreases in some sea grass species, UF researchers noted an increase in other species that require less light, adding to the theory that the quality and clarity of the water in these areas is being negatively affected.

Hale said researchers surveyed 188 spots in a 2,300-square-mile area from Anclote Key north to Piney Point along Florida’s west coast. The area includes the second-largest expanse of sea grass in the eastern Gulf of Mexico and six of the seven sea grass species that are native to Florida.

“When we study sea grass, we need to know first where it occurs and under what environmental conditions,” Hale said. “Then we can start to ask specific questions about what happens to the sea grass when environmental conditions change. For instance, how might increased nutrient concentrations in estuaries adjacent to coastal rivers have affected sea grasses, considering the changes we have observed in their distribution?”

The new UF study, based on a similar survey of sea grasses along Florida’s west coast in the late 1970s, will provide long-term data on sea grass growth and occurrence for the first time, he said.

“We want to be able to compare distribution of these sea grasses to how they were 20 or 30 years ago,” Hale said. “It’s important to maintain a long-term monitoring database to see if we can detect environmental changes that may have occurred, whether from natural or human-made causes.”

Results from the study, which was co-authored with scientists at the Southwest Florida Water Management District in Brooksville and Florida Marine Research Institute in St. Petersburg, were published earlier this year in the journal Estuaries.