Gymnodinium breve

Gymnodinium breve (G. breve).

What do we know about red tide??? These unarmored dinoflagellates are 20-40 mm in size. They produce toxins that affect the central nervous system of fish, leading to mortality in high concentrations. They can also cause severe respiratory problems in humans. Occurring primarily in coastal waters of the Gulf of Mexico, the red tide usually turns water reddish brown when concentrations are high, due to selective absorption of light by its pigments.

These phytoplankton are not actually associated with tides at all, although they are thought to be entrained and transported north by the Loop Current and eddies that it sheds, then travel east toward Florida or west toward Texas. The organisms are found regularly in bays and estuaries of Texas, but high concentrations over large areas result in "blooms" typically occurring in late summer and fall. While the life cycle is not well understood, blooms are known to be related to complex interactions between salinity, nutrient concentrations, and sea state. The characteristic cycle of a bloom involves initiation followed by growth that exceeds predation and natural losses, then a "maintenance period, and finally dissipation that is often associated with mixing of water masses by winds and currents. The algae are concentrated at the surface of the water, thereby allowing them to often be "seen" by sensors on aircraft or satellites, although they can exist to depths of 50m.

Although blooms are known to have occurred for 500 years, there has been an alarming increase in reports in the past 10 years, leading to concern that these blooms are triggered by changes in the earth's ocean-atmosphere system caused by man. Additional information is contained at the following sites: http://www.redtide.whoi.edu/hab/ and http://www-ocean.tamu.edu/~pinckney/texhab.html