Red Tides To The South


Red Tide, bane of Florida beaches, marks its annual return

Earlier this week, according to the Tampa Bay Times, thousands of dead fish washed up on several beaches in southwest Florida, including Treasure Island, John’s Pass, and St. Pete Beach.  Work crews quickly combed the areas and disposed of the fish, which are often killed in the yearly return of the “red tide.”

What is red tide?

The name derives from the crimson color the ocean turns in places where a certain type of alga — a plantlike organism known as phytoplankton — undergoes explosive growth.  “Harmful algal bloom” (HAB) is the preferred scientific term, and the specific type of alga involved is known as Karenia brevis, named after Dr. Karen Steidinger, a scientist who studied the dinoflagellate for the Fish and Wildlife Research Institute.

While red tides occur naturally throughout the world, K. brevis is unique to the Gulf of Mexico.  These single-celled creatures are so small — 1/1000th of an inch in length — they can only be seen via an electron microscope; dangerous concentrations are considered those beyond the threshold of one million per liter of lab-tested seawater.  The alga’s abnormal growth rates can be traced to areas far offshore, up to forty miles away, where the HABs eventually ride ocean currents to beaches throughout the Gulf Coast.

Because K. brevis cannot tolerate freshwater, red tide does not impact rivers or lakes.  Other types of alga — cynobacteria, for example — do thrive in freshwater and are capable of transforming ponds or streams to various other colors like green, brown, or yellow.  Late summer and early autumn months are the most likely times of year for red tide.

What causes harmful alga blooms?

Scientists have yet to pinpoint the exact causes of red tide.  They are investigating potential environmental triggers that may set off toxic alga blooms.  If the red tide moves close to shore the alga’s growth will exacerbated by human. Raw sewage flowing into the ocean, for instance, or certain types of agricultural fertilizers that run off into the sea during heavy rains.



Is it harmful to humans?

For the most part, no.  We don’t recommend swimming on areas affected by red tide because it can cause skin irritation or respiratory issues. Itchy eyes and throat, and coughing or sneezing are the most common symptoms.  People particularly susceptible to breathing issues — children, the elderly, or those with asthma — should stay away from beaches during times of red tide.

Is it harmful to other animals?

For some species, harmful alga blooms prove lethal.  When K. brevis dies, it releases brevetoxin.  These brevetoxins disrupt neurological processes and can lead to neurotoxic shellfish poisoning.  This is the cause of mass fish kills like those seen this week in Florida.

Birds that eat infected fish can also die in mass bird kills, as the toxins work their way up an ecosystem’s delicate food chain.  Dolphins and sea turtles are also vulnerable to the neurological effects of brevetoxins.

Typical wave motions aerosolize these toxins, which are able to harm species that don’t even breathe underwater.  Manatees are the most noticeable example, as certain red tides have been known to kill manatees in large numbers.  In 2013, a record year for manatee deaths, 276 kills were officially attributed to red tide.

When K. brevins goes airborne due to ocean spray. According to him manatees can inhale ocean spray.  Moreover, the alga settles in beds of sea grass that make up the bulk of the manatees’ diet.  Ingesting large quantities of the alga will negatively affect a manatee’s natural buoyancy and hinder its respiration.

Some Shellfish can feel the impact.  Filter-feeders like clams, mussels, and oysters accumulate the alga, potentially causing neurotoxic shellfish poisoning in humans who harvest and eat them.  Scallops are okay to eat, so long as the scallop muscle is being ingested and not the entire animal.  Shrimps, crabs, and lobsters likewise are unaffected.

Use common sense and don’t walk your dog along affected beaches.  The alga may get in your pet’s fur, and dead fish washed ashore can carry other harmful types of bacteria.

Is restaurant seafood safe?

Yes, seafoods are tested for brevetoxins.  That goes for food sold at seafood markets too.

We don’t recommend to eat recreationally-caught fish from areas experiencing red tide. Freezing or cooking the seafood does not destroy the toxins on affected fish. And since brevetoxins have no distinct smell or taste, they’re nearly impossible to detect.

What should we do?

Honestly, there isn’t much to do.  Red tides have plagued the state for hundreds of years, with witness reports dating back to Spanish Conquistadors as early as the 1500s.  Without understanding the causes of red tide, scientists have been unable to pinpoint ways to fight it.  Harmful alga blooms typically last a few weeks, but some can drag on for months at a time.  Eventually winds and currents disperse the high concentrations of K. brevis as new water works its way to the shoreline.

Outside of the environmental effects, red tide poses economic issues as well. Many city governments in Florida act quickly to clear up beaches when HABs do occur because tourism revieved an adversely impact.  While the most likely areas affected are beaches on the southwest Florida coast, anywhere along the Gulf of Mexico may experience harmful alga blooms.

I should worry?

Not at all.  Don’t cancel your vacation plans to the Sunshine State.  In fact, because Crystal River and Homosassa Springs in Citrus County are freshwater, the risk of red tide here is nonexistent.  So you can feel one hundred percent safe when swimming in localsprings or snorkeling with the manatees.

Contact Bird’s Underwater to schedule a nature tour, and come experience King’s Bay for yourself.  Call now for a reservation at 352-563-2763.