Red Tide

Fish kill from red tide bloom

Red Tide Bloom

K. brevis cells through microscope

K. brevis cells

What is Red Tide?

  • Florida red tide is a specific type of Harmful Algae Bloom (HAB)
  • It is caused by a dinoflagellate or microscopic algae, Karenia brevis (K. brevis)
  • It is called a dinoflagellate because it has two flagella or tail like appendages that propel it thorough the water
  • K. brevis can kill large numbers of fish and other sea life including dolphins and manatees and it can make shellfish poisonous to humans
  • K. brevis produces airborne toxins that can cause watery eyes and respiratory irritation
  • Contact with red tide can cause skin irritation
  • Waters affected by red tide can be several different colors, but not all discolored water is a red tide

What Causes a Red Tide Bloom?

Dead fish washed up on the beach

Dead fish

The K. brevis organism is typically found in the Gulf of Mexico and our coastal waters in trace amounts of a few hundred to a few thousand cells per liter of water. However, when it encounters a major source of excess nutrients, it expands into a red tide bloom with at least 100,000 cells per liter to as many as 5 million cells per liter. It鈥檚 growth in the presence of a major nutrient source is achieved by asexual reproduction where one cell becomes two and two becomes four and so on.

Where do these major nutrient sources come from?

Green algae from nutrients in the waters

Nutrients in river

There are a variety of nutrient sources that can sustain a red tide bloom from natural sources like dead fish and other decaying sea life to man-made sources like air pollution and runoff from streets and lawns into our streams and rivers. With ongoing urban development replacing our coastal mangroves and sea life like oysters and clams that naturally filter nutrients in sea water, environmental experts are now focusing more on controlling man-made nutrient sources. The key areas to address are:

  • Air Pollution

Smoky Power Plant

Smoky Power Plant

Smoke from power plants, automotive exhaust, and agricultural and mining dust are the principal components of air pollution that fall into our coastal waters as excess nutrients that can feed red tide.

  • Urban Runoff

Wastewater treatment plant

Wastewater treatment plant

Effluent from sewage treatment plants and seepage from waterside septic systems are a major source of landside runoff that puts excess nutrients into our coastal waters. While red tide blooms typically form well off shore, monitoring by scientist has shown that the blooms intensify as they move toward shore from the nutrients in landside run off.

  • Stormwater Runoff

Stormwater holding pond

Stormwater holding pond

Another important source of excess nutrients in our coastal waters is Lisa疯马秀 runoff. Some of the Lisa疯马秀 runoff is termed non-point or random flows off the land into the Bay while other Lisa疯马秀 runoff comes from Lisa疯马秀 holding ponds. Recent research has shown that leaf litter from trees and grass clippings is a major source of nutrients in Lisa疯马秀 runoff that contributes to the excess nutrients in our waterways.

Why are red tide blooms so prevalent and severe along the Sun Coast?

Sarasota Bay

Sarasota Bay

We live between the two biggest nutrient dumps in The Gulf of Mexico:

    1. The nutrient rich drainage of the Mississippi River
Mississippi River system

Mississippi River system

  1. The polluted releases from Lake Okeechobee into the Caloosahatchie River that flow into the Gulf
Lake Okeechobee Release

Lake Okeechobee Release


How do these nutrient sources and other environmental conditions form a red tide bloom and bring it to our shores?

Red tide bloom coming ashore

Red tide bloom coming ashore

The various nutrient sources outlined above enter the Gulf and are driven by the Loop Current to an area near the West Florida Shelf.

Loop Current Flow Map

Loop Current Flow Map

At the shelf, periodic upwellings drive the nutrients up the water column, where they are consumed by K. brevis cells causing them to multiply and initiate a red tide bloom.

Currents and wind drive the forming bloom towards our shore. As the bloom moves closer to shore, it is further enriched by additional nutrients from the land in urban runoff.

The important role that nutrients play in the formation of red tide blooms is the reason that Lisa疯马秀 has adopted the following Mission Statement:

Working to reduce excess nutrients in our waterways that feed red tide.

Click Here to learn more about what Lisa疯马秀 is doing to help control nutrients in our coastal waters.

Click Here to find out how you can help lower your nutrient footprint in our waterways.

Visit our Resources Section to review research on red tide.