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“Red Tide” is the common term for a particular type of harmful algal bloom made up of large concentrations of toxic red dinoflagellates called Karenia brevis (K. Brevis). These are tiny red-colored, naturally-occurring aquatic microorganisms which, in sufficient concentrations, can cause a reddish tint to the water. At very high concentrations, they can cause toxic or harmful effects on people, fish, shellfish, marine mammals, and birds.
Delaware last experienced a red tide in late August and early September of 2007. It was the first documented occurrence of Karenia brevis north of Cape Hatteras, North Carolina. The organism is primarily found on the Gulf Coast of Florida. Scientists believe that an eddy from the Gulf Stream brought K. brevis to Delaware’s near-shore waters.
Although Delaware has not experienced another bloom of K. brevis, the State continues to monitor for harmful algae blooms such as those which cause red tides.
K. brevis produces brevetoxin, which may be released and aerosolized when the organism is broken up in the surf. The aerosolized toxin has been documented by Florida officials to cause respiratory irritation in the general public when levels reach 100,000 to 200,000 cells per liter. Effects may include coughing and/or asthma-like symptoms.
Maximum confirmed densities during the 2007 Delaware bloom were 14,000 cells per liter.
|Level||Cells Per Liter of K. brevis||Possible K. brevis Effects|
|Present||Background Levels (1,000 or fewer)||None|
|Very Low-a||From 1,001 to 4,999||Possible respiratory irritation in sensitive individuals|
|Very Low-b||From 5,000 to 10,000||Possible respiratory irritation in sensitive individuals|
and shellfish harvesting closures
|Low-a||From 10,001 to 49,999||Respiratory irritation more likely in general population;|
but not widespread
|Low-b||From 50,000 to 99,999||Respiratory irritation more likely; possible fish kills|
|Medium||From 100,000 to 999,999||Respiratory irritation likely in general population; probable fish kills|
|High||1,000,000 or more|| Respiratory irritation likely in general population; probable fish kills;|
and discoloration of the water