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Why we get red tide blooms

SARASOTA COUNTY, FL (WWSB) - Red tide is caused by an agal bloom of micro organisms called Karenia brevis. It is commonly know as Florida red tide to distinguish it from the other types of K. brevis that exist. It is naturally occurring and as old as the hills. Some think it has been described in the Iliad and in the Bible. An article published in a science journal dated 1881 recounts a fish kill observed by Bradenton resident M.A. More as killing cargo loads of fish.

The way red tide kills fish is unlike other algae which kills by sucking the oxygen from the water.  Florida red tide produces a neurotoxin that attacks nerve tissue.

What triggers an explosive Florida red tide growth is unknown, but current theory supports the need for nutrient rich water.  That environmental condition can be produced by upwelling that occurs when surface water is carried away by the wind and current and deep Gulf nutrient rich water replaces it by flowing up from below. It is also possible that nutrients can be supplied by agricultural runoff from rivers like the Peace River, Caloosahatchee River, Hillsborough River, Manatee River and others.

Siesta Beach red tide fish kill

It is important to note that a direct link between large-scale coastal farming and massive Gulf algae blooms of other varieties has been established. These algae blooms are responsible for our so called "Gulf of Mexico dead zones" where oxygen depleted waters overwhelm marine ecosystems.

However, a direct link between Florida red tide and agricultural runoff has not yet been established. Research has suggested that our red tide blooms do coincide with an increase in river outflow (such as might occur in the wet season) but the exact combination of chemical, physical and biological factors necessary for our type of algae blooms still requires additional study.

Florida red tide is ever present in off shore Gulf waters. It usually bothers no one. So long as the growing algae is diluted at a fast enough rate then there is no problem. But that did not happen this time. Why? Well, we know 3 things:

1) You need the right mix of ingredients to concentrate the algae near the shore.

2) You need the right mix of ingredients to increase the rate of algae growth.

3) You need the right mix of ingredients to transport the effects of the bloom, such as fish kill and airborne irritants, on the coast.

According to the National Ocean Service the "Loop Current is an area of warm water that travels up from the Caribbean, past the Yucatan Peninsula, and into the Gulf of Mexico". It forms a permanent circular like current in the Gulf but its position varies. Turns out it is critical to Florida red tide blooms.

When the loop current has drifted south there is a free exchange of open Gulf of Mexico water and the near shore Florida waters. This exchange helps dilute the algae.

In March, for instance, the loop current was south and we had no red tide problem. Then it began to creep northward. Now the loop current is in its northern location.

Now the edge of the loop current buts up against the shelf waters and, by way of physical characteristics of fluid flow, creates a fast jet of water that separates the two. In other words, when the loop is north it creates a force field that prevents the free exchange of water with the open Gulf and the near shore waters. Read that as no algae dilution. With that, the first condition above was meet.

If other conditions are correct the concentrated near shore algae will have a growth spurt. That happened this time and condition 2 above was meet, although the exact reason why is still being studied.

Add to that the southward movement of the Bermuda high which directs our summer winds. They have been out of the southwest a great deal of the time. The reason for that is also being studied. It could be a natural cycle or it could be more. In any event it caused the airborne toxins released by the red tide and injected into the air by sea foam to reach the coast. Condition three above was meet.

Additional study is needed with this complex problem. Only scientific research and a willing society can perhaps influence the outbreaks of blooms down the road.

John Scalzi