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Drift algae appears in Pine Island Sound

By Staff | Mar 3, 2009

According to Sanibel-Captiva Conservation Foundation Marine Lab scientists, mats of drift algae were witnessed and photographed in Pine Island Sound off Punta Rassa on Feb. 24.

SCCF’s Marine Lab scientists have been observing increasing amounts of algae growing thickly on seagrasses around Sanibel since November, discovering the latest mats during the past 10 days.

Recently, local fisherman and a resident living on a canal along the river have contacted SCCF about a yellow-brown algae interfering with their fishing, netting and covering the rocks along their canals.

“This brown filamentous macroalgae is called Hincksia mitchelliae, and it can drastically reduce light for the blade it grows on as well as surrounding blades,” an SCCF staff report stated. “Seagrasses need light for photosynthesis, and if the algal coverage is excessive, seagrass growth can slow or even stop.”

Marine Lab scientists have also observed many other species of macroalgae distributed throughout southern Pine Island Sound, from Captiva to Dixie Beach to Shell Point.

Last summer’s rains, including Tropical Storm Fay, brought a lot of nutrient-enriched water into the river and estuary. This impacts the estuary in several ways. In the natural system, there is a balance between saltwater and freshwater, the amount of nutrients in the water, and the plants in the water and the grazers that feed on them. In our manipulated and disturbed system, that balance has been destroyed.

The water from this past summer, both that released from Lake Okeechobee as well as water from the Caloosahatchee basin, is high in nutrients. High nutrient levels can support an increase in the growth of algae once the water is clear enough.

In addition, the increased freshwater flow causes abnormal salinity fluctuations and hypoxic events (lack of oxygen available in the water column), which could reduce the number of benthic invertebrates which would normally feed on algae and keep it in check. There has also been an increase in the nutrients that fuel algae growth and a corresponding decrease in the grazers that could help keep the algae in check.