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NASA Satellites Detect 'Glow' of Plankton in Black Waters
Although just microscopic ocean plants, phytoplankton are the building blocks for the entire marine food chain. And, since they require sunlight, water, and nutrients for growth, they serve as a good indicator of changes in the environment. Sunlight is most abundant at and near the sea surface, so phytoplankton flourish near the top layer of the ocean. Also like plants on land, phytoplankton contain the pigment chlorophyll, which gives them their greenish color. During photosynthesis, chlorophyll in plants use sunlight as an energy source to combine water molecules with carbon dioxide into food.

Image of Florida red tide bloom of Karenia Brevis and the inset shows the bloom under a microscope. Image to right: Florida red tide bloom of Karenia Brevis on left. The inset image shows Karenia Brevis under a microscope. Click on image to enlarge. Credit: Woods Hole Oceanographic Instititute/NOAA and NOAA/CHBR

Phytoplankton "blooms" occur when nutrient and sunlight conditions are just right. Although scientists have been able to view these blooms using satellite data over the past 25 years, they have been unable to distinguish early blooms from poor water quality, like that caused by agricultural runoff.

Now for the first time, researchers may detect a phytoplankton bloom in its early stages by looking at its red "glow" under sunlight, thanks to unique data from NASA satellites. This technique can warn fishermen and swimmers about developing cases of red tides - a common name for the blooms of a certain phytoplankton species that contains reddish pigments and turns the water red.

Red tides occur every year off Florida and are known to cause kill fish, harm and kill coral, and cause skin and respiratory problems in humans. Previous studies have also shown that "red tides" occur within plumes of dark-colored runoff from rivers, wetlands, and farms, causing "black water events."

The left image was captured by the MODIS instrument on Oct. 19, 2003 and shows abundance of the red tide bloom.  The right image shows the chlorophyll fluorescence in the water.Image to left: The left side image was captured by the MODIS instrument on Oct. 19, 2003. Overlaid were the locations where water samples were collected to determine their Karenia brevis (toxic phytoplankton) abundance between Sept. 19 and Oct. 19, 2003. Large circles mean higher abundance. Smallest circles mean "not present." The dark plume flows from the central Florida coast to the Dry Tortugas. The image on the right is from the same time period. It shows MODIS chlorophyll fluorescence. The fluorescence increases from dark blue to green, yellow and red. Credit: NASA/USF

In this study, scientists from the University of South Florida used data from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard NASA's Terra and Aqua satellites. MODIS detects the glow, or fluorescence, from the plant's chlorophyll. Without this data, it is impossible to separate phytoplankton blooms from plumes of dark river runoff that may contain few individual phytoplankton cells.

Specifically, the researchers used the satellite data to study the nature and origin of a dark plume event in the fall of 2003 near Charlotte Harbor, off the south Florida coast. Moderate concentrations of one of Florida's red tide species were found from water samples.

The left image is a MODIS image which shows dark water on Oct. 9, 2003. In the image on the right, the white lines on this color enhanced image depict the approximate locations of Everglades rivers. Image to right: The left side image is a MODIS image which shows dark water on Oct. 9, 2003. The arrows show the average wind speed and direction (day and night) from the QuikScat scatterometer. Oct 8-14 is in black, Oct. 15-19 is in red. The image on the right hand side shows Everglades River areas of low salinity. Areas of low salinity or salt usually occur near the mouths of rivers. In the image on the right, the white lines on this color enhanced image depict the approximate locations of Everglades rivers. Credit: NASA/USF/NOAA/UM

The study traced the black water patches near the Florida Keys to some 200 kilometers (124 miles) away. The results suggest that the delicate Florida Keys ecosystem is connected to what happens on land and in two remote rivers, the Peace and Caloosahatchee, as they drain into the ocean. Extreme climate conditions, such as unusually high rainfall in spring and summer 2003 may have accelerated such connections.

The link between coastal runoff and black water events is an example of how land and ocean ecosystems are delicately linked together and why coastal and land managers must work together to prevent future black water events.

For more information, please check out these related links:

NASA's Top Story Page

Red Tide

NASA's MODIS Instrument

Florida 2002 "Black Water" Event

"Glowing Algae" Story

Information on phytoplankton

Mike Bettwy
NASA Goddard Space Flight Center