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Effects of Brown Tide in the Indian River Lagoon (2012)

After receiving reports of discolored water in the northern Indian River Lagoon during early July 2012, researchers from the Florida Fish and Wildlife Conservation Commission (FWC) and partners from the St. Johns River Water Management District and the University of Florida analyzed water samples to find the cause. The culprit? A bloom of brown tide algae identified as Aureoumbra lagunensis. Brown tides occur naturally and can be common in waters with high salinity. The brown tide algae have been noted from Florida to Maine on the east coast and throughout coastal areas of the Gulf of Mexico, but this is the first time FWC has documented a bloom of the algae in state waters.

Brown tide organisms are nontoxic and there are no known human health concerns, but shellfish and fish kills can occur during blooms. Shellfish can be especially affected, as brown tides produce mucus that can prevent shellfish from feeding. A sustained bloom could impact shellfish populations in the northern Indian River Lagoon. Fish kills can occur when the algae deplete oxygen from the water. The public can report fish kills or fish with abnormal behavior to the FWC’s Fish Kill Hotline. Eating fish is an important part of a healthy diet. However, the Florida Department of Health advises that fish or wildlife found dead or dying not be touched, collected or eaten.

Seagrass can be affected by the bloom as well, potentially leading to more far-reaching impacts. Brown tides can reduce water transparency to less than a foot in some cases, affecting seagrass by limiting light penetration in the water column. Currently in some areas of the lagoon, the brown tide is co-occurring with a bloom of Pyrodinium bahamense, which can also discolor water and reduce visibility. These effects are compounded by a long-term phytoplankton bloom of Pedinophyceae algae, which clouded the water from March 2011 to as late as March 2012.

With seagrass loss, fish species that rely on seagrass for protection from predators or for a source of prey may travel to different locations. Seagrass is a major food source for manatees, and reductions in its availability may impact manatee distribution.  Manatees may move to other locations in search of food, or feed in shallower areas where seagrass is less impacted by reduced light penetration. Boaters are asked to use caution in these habitats.

FWC and partners, including the St. Johns River Water Management District, continue to monitor the Indian River Lagoon and potential impacts of these algal blooms. NOAA Harmful Algal Bloom Event Response program provided event-response funding to researchers at Stony Brook University to further investigate this bloom.

For additional information:

St. Johns River Water Management District Indian River Lagoon Update

Indian River Lagoon National Estuary Program

Florida Department of Agriculture and Consumer Services-Shellfish Harvesting Area Status

Florida Department of Health Florida Healthy Beaches Program

Florida Department of Health Fish Consumption Advisories