By Kerry Schofield
ST. PETERSBURG — A study by the University of South Florida reported that a widespread red tide bloom in 2005 may have been caused by high amounts of submarine groundwater discharge from the 2004 hurricane season. The red tide bloom affected coastal waters off west-central Florida from January 2005 through January 2006. It killed fish, turtles, birds, marine mammals and organisms living near the ocean bottom.
University of South Florida St. Petersburg Associate Professor Chuanmin Hu is a researcher in optical oceanography with the college of marine science. He studies toxic algal bloom images from the Moderate-Resolution Imaging Spectroradiometer Fluorescence Line Height (MODIS FLH) NASA satellite.
“My expertise is to look at this alga from space, Hu said. “It’s just like taking a photo.”
Hu explained that the MODIS satellite sees ocean algae, river runoff, oil, and suspended particle forms in different shades of black. An algorithm is applied to the images that determines what type of substance is present. Once red tide is confirmed by satellite imagery, the Fish and Wildlife Research Institute in Florida collects water samples for testing to determine if the toxic algae is present.
“It can be seen in patches if it’s 20 miles off shore,” Hu said. “We look at primarily the west Florida shelf, our neighborhood, off the eastern Gulf of Mexico.”
Hu said the red tide patches are measured in pixels. Each pixel is associated with an estimated area the size of one square kilometer or 200 meters. The widespread bloom in 2005 was equivalent to 50 times the size of Lake Okeechobee and covered the entire west Florida shelf with depths up to 150 feet. Typically, a red time bloom is three to five times the size.
The 2006 study suggests higher than average rainfall from the 2004 hurricane season caused elevated groundwater runoff that provided nitrogen-rich food for the massive 2005 red tide bloom. Hu explained that red tide is a tiny, leafy plant about the size of a strand of hair. The toxic plant can swim and shake and is a living species.
“During daytime, if they need light, they swim to the surface and at night, they swim to the bottom,” Hu said. “They are very smart.”
Hu said that because red tide is a plant, it must eat nutrients to live. It eats natural fertilizers in the ocean and competes with other plants for food. Groundwater runoff provides food for the plant also.
“Any land-based runoff is a nutrient,” Hu said. “It has fertilizer, it has a lot of agricultural things and everything goes to the ocean.
Hu said these plants are harmful because they contain toxins. When the plant dies, it sinks to the bottom of the ocean and releases the toxin into the water. Big fish eat small fish that have eaten the toxic plant and in turn birds eat the fish resulting in death.
“It’s a chain and there’s toxin in that algae,” Hu said. “It’s like a snake, so they die.”
Hu said that when humans inhale the toxin, they suffer from an infection and become sick. Small children with under-developed immune systems can possibly die from the toxin. Many human deaths occur worldwide from red tides. Different species of toxic algae inhabit the waters of Japan, China, Australia and England.
“In Maine, they call it brown tide,” Hu said. “It is a different species and has a different characteristic.