Dr. Suri Sehgal

At this time of the year, South Florida is often threatened with either blue-green algae or red algae blooms or both, collectively known as harmful algal bloom (HAB). We have been spared the wrath of both so far this year.

Although they are lumped together under HAB, the two are not technically algae. The blue-green organism is a single-cell bacterium called cyanobacteria, whereas the red tide organism is a single-cell dinoflagellate called Karenia brevis (K.brevis). The former has chlorophyll and can synthesize its own food, and the latter has flagella that help it to be mobile and swim around. This misnomer will perhaps be corrected by the scientific community someday.

Between May and June of this year, 330 elephants were reported dead in Botswana, a land-locked country in southern Africa, according to wildlife officials there. The cause of their death has been attributed to the ingestion of cyanobacterial neurotoxins through drinking water from a lake loaded with cyanobacteria (blue-green algae). This news raises a red flag for those of us who live on the islands and get our water supply from Lake Okeechobee, which is laden with cyanobacteria.

The cyanobacteria flourish in polluted water rich in excess phosphorous and nitrogen. The lake has plenty of both. The lake is fed by water from the Kissimmee River from the north that is laden with organic and inorganic nutrients from ranches, farms, and septic tanks along its basin; and, during the wet season, back-pumping of the chemically polluted excess water from the Everglades Agricultural Area (EAA) in the south.

Just a century ago, water flowed down the Kissimmee River into Lake Okeechobee, then south to the Everglades marsh into the flats of Florida Bay. These days, there is very little southerly flow of water from Lake Okeechobee. More than two-thirds of the rainwater that used to flow south into Florida Bay is instead being flushed untreated into the St Lucie estuary on the east and Caloosahatchee River estuary on the west. Unfortunately, these releases devastate the downstream Caloosahatchee River, estuary, and coastal ecosystems by spreading toxic blue-green algae. The excess nutrients fuel the growth of blue-green algae, impacting our drinking water supplies, and making the local beaches unsafe for swimming and fishing. Last week the U.S. Army Corps of Engineers was scheduled to announce discharges from Lake Okeechobee in order to bring down the water level in the lake to protect the Herbert Hoover Dike. Hopefully the discharge will not affect the water quality as the lake is mostly free of blue green algae this year.

Unlike cyanobacteria, the red tide organisms prefer saltwater and do not do well in lower salinity waters. They multiply rapidly in the open ocean and reach epidemic proportions about 10 miles to 40 miles offshore where there are limited nutrients. The high tides or other events bring them to the shore where the toxin is released, wreaking havoc with marine life and human health. The polluted waters along the coast probably have an effect on their multiplication, but more research is needed to determine the impact of nutrients on their multiplication and growth.

From 2017-2019, toxic red tide was a lot in the news because of its severity, long duration, large-scale kill of marine life, respiratory problems in humans, and the financial loss from the decline in tourism.

Dr. Cynthia Heil, director of the Red Tide Institute at Mote Marine Laboratory in Sarasota, has discovered “helper” type saltwater cyanobacteria that show up as a precursor to red tide. This can fix atmospheric nitrogen into digestible food for the red tide in the open ocean.

Both blue-green algae and red tide organisms produce toxins that are harmful to humans and wildlife. The blue-green toxins are called microcystins, and BMAA. The ingestion of microsystins in significant amounts can lead to skin irritations, trigger allergies, vomiting, and even liver failure. People and animals can become sick by drinking or bathing in water contaminated with cyanobacteria. Apparently this is what happened to the elephants in Botswana, as an elephant can drink an average of 50 gallons of water per day.

The ingestion of BMAA can lead to neurological diseases such as Lou Gehrig’s (ALS), Alzheimer’s, and Parkinson’s, as per Howard Simon, a Sanibel resident and the president of the Clean Okeechobee Waters Foundation, and Dr. Walter Bradley, former chairman of the University of Miami’s Department of Neurology.

Red tide produces toxin called brevetoxins. In high concentrations, it affects the central nervous system of fish and other marine wildlife. This toxin also causes fish kills. When there is red tide, one can see dead fish littered on the beaches. In 2018, many dolphins died from red tide poison, and as a result their sightings have become infrequent while boating in the estuaries. Their populations have yet to come back to pre-2018 levels.

More research on HABs is needed to develop polices to mitigate their impact. Considering the seriousness of the problem, researchers at various institutes, such as Mote Laboratory, Florida Gulf Coast University, and Florida Fish and Wildlife Institute are developing technologies to mitigate it. But none of the controls suggested so far, whether biological, chemical, or mechanical, are economically feasible. The only feasible strategy is to maintain a balanced salinity level with a minimum flow level of water from the lake all year around and decreasing the number of high discharge flood control events in the wet season. Also, it is more important that nitrogen and phosphate levels stay within acceptable limits for good estuary health.

Recognizing the problem, Gov. Ron DeSantis reactivated the dormant Blue-Green Algae Task Force in 2019 to prioritize actions and make recommendations to reduce impacts of HABs in Florida waters. Florida legislators incorporated some but not all recommendations of the task force in Senate Bill 712. The governor signed SB712 “The Clean Waterways Act” earlier this year. Professor Mike Parsons, of the FGCU, calls this a good first step in addressing water quality problems, but a lot more needs to be done considering the severity of the problem.

Captiva resident Dr. Suri Sehgal has a long career as a crop scientist, seedsman, entrepreneur and leading expert in the global hybrid seed industry and now operates two nonprofit organizations with his wife, Edda. He is a member of the Captiva Sea Level Rise Committee and chairs the Captiva Island Yacht Club’s Environmental Awareness Committee.