Red Tide Develops Off Florida

Red tides are not unusual in the waters of the Gulf of Mexico off the western coast of Florida. They give off a strong smell, irritate the eye, nose, and throat, and sometimes cause large fish kills.

Red tides are caused by tiny algae that grow on the surface of the ocean, occasionally giving it a reddish-brown tint. Satellite images can be used to map the extent of red tides and monitor how they spread over time. Satellites detect changes in the way the sea surface reflects light. These changes can be linked to concentrations of chlorophyll, showing where algae and other ocean plants are concentrated in the ocean.

In mid-November 2004, scientists began to notice an algae bloom developing in the Gulf of Mexico, and ground tests confirmed the presence of red tide. By Dec. 8, the bloom had spread to cover 400 square miles. The images above show chlorophyll concentrations in the Gulf of Mexico off southwestern Florida on Oct. 30 (bottom right corner) and Nov. 21, 2004 (left), as well as chlorophyll fluorescence (upper right) on Nov. 21.

Highest concentrations of chlorophyll and highest levels of fluorescence are red; lower values are green and blue.

The red tide is clearly visible as the oval-shaped red area to the west of the shore in the Nov. 21 image from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) flying on the OrbView-2 satellite. The high chlorophyll concentrations occur between Charlotte Harbor and the Florida Keys, which matches the location of the bloom.

-- LiveScience Staff

Credit: SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE. MODIS fluorescence image courtesy the Institute for Marine Remote Sensing (IMaRS), College of Marine Science of University of South Florida