Saturday, December 4, 2021

Red Tide…It’s not here but be in the know!



Checked weekly by state scientists at many locations along the Marco Island shore and offshore Collier County, there has not been a presence of the Red Tide in our area in many months. Log on and sign up for daily email reports for Naples and Marco Island beach conditions at

While the phenomenon of Red Tide is worldwide, in Florida it is caused predominantly by the organism Karenia brevis. This micro algae species is a dinoflagelate that naturally occurs or “initiates” in the Gulf of Mexico (and can be found in the Atlantic along Florida’s coastline). When circumstances are optimum, the algae population will bloom or reproduce rapidly so the explosion of organisms causes discoloration of the water, or a Red Tide. “Red” is not always the coloration of the water; it could look muddy, brown or, if a sustaining and large bloom, rust colored, hence the name, Red Tide. This type of dinoflagelate bloom is described as a Harmful Algal Bloom or HAB.  When an HAB happens it can kill fish, make shellfish poisonous for human consumption, and release toxic irritants that cause respiratory irritation that drives beach goers and tourists off the beaches.

With modern day science and extensive water quality analysis along the coasts of Florida, Red Tide is still a big mystery as to why or what initiates it and what sustains it. Red Tide has been documented since the 1800s in the Gulf of Mexico in all months of the year. Some scientists have speculated that the Caribbean waters, when incorporated into the Loop Current in the Gulf of Mexico, are pushed against the coastal shelf, creating an upwelling of nutrients, which in turns creates the conditions for an algae bloom to nearby shore waters. Nutrients, natural and manmade, don’t cause, but can sustain and prolong a near shore bloom causing havoc for sea life, beachgoers, and coastal residents. Important to note, Karenia brevis uses both types of nutrients. Added to the mystery is the oil leak disaster.  Will oil dispersants in the Loop Current affect algal blooms? Researchers and scientists are studying Gulf of Mexico waters, currents, and concentrations of organisms. Some studies could shed light on some of the algal bloom mysteries.

Should you swim during a Red Tide event? For most people it is not a concern, but if you have upper respiratory issues or sensitive skin, swimming is at your own risk. When HAB concentrations are in a moderate level in Collier County, signs at public beach accesses are posted to warn beach goers IF there is the presence of Red Tide. (In Marco, the signs are at Tigertail Beach and South Beach access, the Marco Island Civic Association Resident’s Beach access and the City of Marco Island beach accesses at the Madeira and Crystal Shores locations). Common sense is necessary to determine if you, family members or friends, could be susceptible to the effects, mainly respiratory irritation, of Red Tide.

Should you eat seafood during a Red Tide event? Commercially caught seafood that is purchased at grocery stores or restaurants is safe as the State of Florida closely monitors Karenia brevis and other toxins in seafood. Recreationally caught seafood during a Red Tide event should be consumed only if the following guidelines are followed:

Finfish – are safe, if caught live, show no signs of distress, are filleted properly and thoroughly cooked.

Crabs & Shrimp – if caught live, there are no signs of distress and cooked properly, are okay to eat since no toxins are absorbed in their flesh.

Oysters, Mussels, Clams (Bivalves) – are NOT safe to consume. Check for daily status and closures of shellfish beds within the State of Florida waters.

Red Tide also affects the environment. The same toxins from a Red Tide bloom can cause very harmful affects to marine animals such as dolphins, manatees, and sea turtles. Breathing on the surface of the water, aerosol toxins from a bloom are present and breathed in causing sickness and mortality. Blooms also cause hypoxic (reduced dissolved oxygen) conditions, killing benthic (sea bottom) creatures and impacting the food chain.

What can a coastal resident do to help prevent a Red Tide event? Be cognizant and always consider water quality protection. Marco Island has over one hundred miles of waterway canals and seven miles of beaches. What one puts in their yard ultimately ends up in the Gulf of Mexico! Check out to learn about planting native plants, which require less water, fertilizer, herbicide and pesticides so less impact to surface waters. Do your part and go native!

Nancy Richie is a long time Island resident and Marine Biologist.

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