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Red Tide

Frequently Asked Questions about the 2018 Red Tide Bloom

This red tide bloom has been trying for everyone. It is hard seeing our coast, our wildlife, and our economy being impacted to the degree that it currently is. Along with the devastation has come a lot of questions. Below are answers to some most commonly asked:

Was this red tide bloom caused by the freshwater released through the Caloosahatchee River? No. The current red tide bloom began in late 2017, long before the current rainy season and freshwater releases. See: An algae problem for related information.

What did cause this red tide bloom? Scientists know that red tide (Karenia brevis) blooms, originate 10-40 miles offshore and winds and currents bring them inshore, usually in bottom waters. Red tide can use many different forms of nitrogen and phosphorus and the sources of these nutrients may differ between the offshore, nearshore, and estuarine environment.

Is the blue-green algae in the Caloosahatchee River fueling the current red tide bloom? Possibly. At a minimum, the nutrients being released through the Caloosahatchee River estuary, and for that matter from all estuary runoff throughout southwest Florida, is likely supplying nutrients to this current red tide bloom. This year is unique in that both red tide and blue-green algae are blooming at the same time. This didn’t happen during the 2016 blue-green algae bloom. As a result, there is much that scientists do not yet know about how or if the two blooms are interacting. These studies are underway now. Scientists do however know that red tide can use at least 12 nutrient sources, and nutrients from estuary runoff is one of those nutrient sources red tide can take advantage of.

Why has this red tide bloom been so bad? A number of factors are likely at play this year. For instance, higher than normal estuary and nearshore nutrients – regardless of source – could be contributing to the intensity and duration of this bloom. Readers may also be aware of the Saharan dust deposits that have been blown into the Gulf of Mexico over the last few months. Iron rich Saharan dust, not only gives us brilliant sunrises and sunsets; it also stimulates the bloom of another blue-green algae called Trichodesmium. Trichodesmium has the ability to fix nitrogen from the atmosphere to ammonium, where it is then available to red tide cells. We’ve also been faced with onshore winds and currents that have resulted in the red tide remaining inshore much longer than typically occurs.

Wait a minute – doesn’t blue-green algae only occur in freshwater? Most blue-green algae does occur in freshwater, but there certainly are marine and estuarine species, Trichodesmium being one. It’s important to note that not all blue-green algae is toxic and for those that are, the level of toxicity is largely dependent upon the specific toxin produced. Trichodesmium do produce toxins, but researchers have not documented any negative effects of Trichodesmium on marine life or people in Florida. In fact only a few specialized organisms are able to consume Trichodesmium.

Did Hurricane Irma play a role in this year’s red tide bloom? Scientists observed turbid waters from nearshore to approximately 30-40 miles offshore for several months after Hurricane Irma; however they don’t specifically know what role if any this played in the present bloom.

Is this the longest red tide bloom on record? No. The longest red tide bloom since the Florida Fish and Wildlife Conservation Commission began collecting data in 1953 lasted 30 months, occurring between 1994 and 1997. Six other red tide events have lasted as long as or longer than our current bloom, keeping in mind of course that this bloom is not yet over.

Is this the worst red tide bloom on record? I guess that depends on how we define “worst.” This is definitely a significant red tide event with serious impacts to fish, marine mammals, sea turtles, residents and coastal businesses. These types of impacts are typical during severe red tide events; however, a larger number of dead fish have occurred during this red tide in Lee and Charlotte counties compared to past severe red tide events, and it’s not over. That said, a 2005 red tide bloom resulted in a 2000 square mile dead zone in the Gulf of Mexico that extended from New Port Richey south to Sarasota. We haven’t seen that yet, but it could be our future. And, in 2015, three red tide blooms occurred simultaneously; one along the coast of Texas, another in the northern Gulf of Mexico from Louisiana through the Florida Panhandle, and a third in southwest Florida. Each of these could be described as unprecedented.

What can we expect as our climate changes? Warmer water due to climate change is predicted to cause algae to bloom more often, more intensely, and in more water bodies. Due to the synergistic relationship between increasing water temperature and nutrients, climate change will also make it harder to control blooms once they’re initiated. As such, it’s imperative that we reduce nutrient inputs to our lakes, rivers, estuaries, and coastal ocean waters today.

When will this bloom end? Hopefully, this bloom will soon go away so that we can get back to normal, but history has shown us that when a bloom occurs throughout the summer it will likely result in a fall bloom. In fact only one summer bloom since 1953 (1960), did not result in a fall bloom.

Is this our new normal? There is no evidence that this is a trend – next year there may be no blooms.


Feature image courtesy of FWC

FWC Red Tide Summary. 2018 email communication

Havens, K. 2018 email communication

Havens, K.E. 2018. The Future of Harmful Algal Blooms in Florida Inland and Coastal Waters. TP- 231, Florida Sea Grant College Program, University of Florida.

O’Neil, Judith M. and Cynthia A. Heil (Ed). 2014. Nutrient dynamics of Karenia brevis red tide blooms in the eastern Gulf of Mexico, Harmful Algae, 38:1-140.


4 Comments on “Frequently Asked Questions about the 2018 Red Tide Bloom

  1. Hi Betty,

    I am coming to Englewood Beach early April from the UK, could tell me if there is still a Red Tide problem along this stretch of water. I know last Summer it was bad in Sarasota so flipped coast lines to Flagler beach on the Atlantic side …

    I like to o a spot of fishing so hoping its gone …

    Warmest regards, Tony UK

    • Hi Tony…At this time there is no red tide occurring anywhere in Florida. Of course that could change, but April is generally not a big month for bloom initiation. You can visit this website: for weekly updates. I hope you have a great time here in SWFL. Betty

  2. My family and I will be staying on Manasota Key the first week in November. Has there been issues with the red tide along those beaches? We are leaving this Saturday. Thank you