NASA’s MODIS instrument captured this image of the southern tip of Florida curving into a blue-green ocean edged by white clouds. MODIS and a new generation of satellite-based sensors can help environmental managers track noxious algae in the Gulf Coast and beyond. Credits: NASA
Harmful algae can endanger public
health and coastal ecosystems and economies. Advances in satellite imaging are
providing new ways to look at our living ocean.
By the time they were over, a
series of massive algal blooms along the west coast of Florida in 2020 would be
linked to some 2,000 tons of dead marine life around Tampa Bay. The human costs
were stark, too, including a double-digit increase in asthma cases in Sarasota
and Pinellas counties, and estimated losses of around $1 billion across
economic sectors from tourism to fisheries.
Earth-orbiting satellites have been
used for decades to detect algal blooms from space, enabling more
frequent observations over broader areas than is possible by directly sampling
the water. The most common observing technique relies on the visible spectrum
to measure ocean color. However, this approach has been mostly restricted to
clear sky conditions.
A recent study, led by scientists at NASA’s Jet Propulsion
Laboratory in Southern California, has shown how one space-based instrument
called TROPOMI, or TROPOspheric Monitoring
Instrument,
was able to peer through thin clouds to uncover powerful clues about Karenia
brevis (or K. brevis), the microscopic algae responsible for the 2020 blooms.
TROPOMI’s enhanced ability to “see” and measure fine wavelengths of light could
potentially help federal agencies and local communities better forecast and
manage harmful outbreaks. (TROPOMI flies aboard the European Sentinel 5P
spacecraft, which was launched in 2017.)
The scientists examined the West
Florida Shelf, a stretch of continental crust arcing from the Panhandle to the
Keys. From its origins in other parts of the Gulf of Mexico, K. brevis is
carried toward the coastline on strong winds and ocean currents. Recent
research has shown that western Florida, like many coastal communities, may be
increasingly vulnerable to outbreaks because these algae flourish in
nutrient-rich, warm conditions fueled by runoff, fertilizer, and climate
change.
Systems for monitoring and
forecasting harmful algal blooms are available in many states and coastal
regions, including the Gulf of Mexico and Great Lakes. The National Oceanic and
Atmospheric Administration (NOAA) works with academic, state, tribal, and local
partners to develop and issue harmful algal bloom forecasts – similar to
weather forecasts – during the seasons when blooms occur.
K. brevis events are especially
concerning because the algae produce a potent neurotoxin that in high
concentrations can cause massive fish kills and poison marine life such as
turtles, manatees, and birds. The toxin can also be inhaled, causing respiratory
illness in humans, and it can accumulate in shellfish, resulting in
gastrointestinal illness in people who consume them.
As the algae feed and grow via
photosynthesis, K. brevis emits a faint red glow called solar-induced
fluorescence (red SIF) that can be detected by some satellite instruments
including TROPOMI, which was actually designed to measure air pollution.
Sifting through TROPOMI data
acquired along the coast of western Florida between 2018 and 2020, the team
found that the instrument gathered about twice as much fluorescence information
emitted by the algae as observed by previous methods that rely on ocean color.
TROPOMI’s advanced imaging capabilities – including four spectrometers
measuring light ranging from the ultraviolet to shortwave infrared – enable it
to penetrate thin cloud cover and obtain measurements of the ocean surface more
frequently.
Space-Based Advantage
The scientists said their findings
demonstrate the value of using TROPOMI by itself or in concert with other
Earth-observing tools such as NASA’s longtime MODIS (Moderate Resolution
Imaging Spectroradiometer) instrument, aboard the Aqua and Terra satellites.
MODIS measures ocean color and is currently being used by environmental
managers in Florida and other places to detect algae on clear days.
Another ocean color instrument –
scheduled to launch early in 2024 – will look at the world’s marine ecosystems
like never before. NASA’s PACE, or Plankton, Aerosol,
Cloud, ocean Ecosystem mission, will study phytoplankton and other ocean biology,
atmospheric aerosols, and clouds in many more wavelengths than previous
sensors. These observations will help forecast the appearance of harmful algae,
as well as the boom-bust cycle of fisheries and other factors that affect
commercial and recreational industries.
“For nearly 20 years, ocean color
sensors have been foundational for satellite monitoring of harmful algal
blooms,” said lead author Kelly Luis, a NASA postdoctoral program fellow at
JPL. “This application of TROPOMI red SIF demonstrates how the combination of
satellite technologies can bolster early warning systems beyond clear sky
conditions.”
Early warning via satellite has
been shown to have real-world benefits. A recent NASA-funded case study found
that early detection of cyanobacteria in Utah Lake led to significant savings on health care, lost work
hours, and other economic losses. A few days of advance warning can translate
to faster action on the ground, including public alerts and even beach
closures.
Jane J. Lee / Andrew Wang
Jet Propulsion Laboratory, Pasadena, Calif.
Source: NASA Scientists Test New Tool for Tracking Algal Blooms | NASA
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