When a series of massive algal blooms on Florida’s west coast ends in 2020, an estimated 2,000 tons of dead marine life around Tampa Bay will be associated with it. Human loss was also significant; There were also double-digit increases in asthma cases in Sarasota and Pinellas counties and an estimated $1 billion in losses in various economic sectors, from tourism to fishing.

Earth-orbiting satellites have been used for decades to detect algal blooms from space, allowing observations to be made more frequently over larger areas than is possible with direct water sampling. The most common observation method relies on the visible spectrum to measure ocean color. However, this approach was mostly limited to clear sky conditions.

A recent study Geophysical Research LettersResearch led by scientists at NASA’s Jet Propulsion Laboratory in Southern California has demonstrated how a space-based instrument called the TROPOMI, or TROPOSpheric Monitoring Instrument, can peer through thin clouds to reveal powerful clues about Karenia brevis. (or K. brevis), the microscopic algae responsible for the 2020 bloom. TROPOMI’s enhanced ability to “see” and measure subtle wavelengths of light could potentially help federal agencies and local communities better predict and manage harmful outbreaks. (TROPOMI flies on Europe’s Sentinel 5P spacecraft, launched in 2017.)

The scientists studied the West Florida Shelf, a section of continental crust that extends in an arc from the Panhandle to the Keys. K. brevis is carried to the coastline by strong winds and ocean currents from other parts of the Gulf of Mexico. Recent research has shown that West Florida, like many coastal communities, may be increasingly vulnerable to outbreaks because these algae thrive in nutrient-rich, warm conditions triggered by currents, fertilizers and climate change.

Monitoring and forecasting systems for harmful algal blooms are available in many states and coastal areas, including the Gulf of Mexico and the Great Lakes. The National Oceanic and Atmospheric Administration (NOAA) works with academic, state, tribal, and local partners to develop and publish forecasts of harmful algae growth, similar to weather forecasts during flowering seasons.

The K. brevis outbreak is particularly worrying because the algae produces a potent neurotoxin that in high concentrations can cause mass fish kills and poison marine life such as turtles, manatees and birds. The toxin can also cause respiratory illness in humans by inhalation, and can accumulate in shellfish and cause gastrointestinal illness in people who consume it.

As the algae feed and grow through photosynthesis, K. brevis emits a pale red glow called solar fluorescence (red SIF), which can be detected by some satellite instruments, including the TROPOMI, which is actually designed to measure air pollution.

Examining TROPOMI data obtained along the west Florida coast between 2018 and 2020, the team found that the device collected about twice as much information about the fluorescence emitted by algae as previous methods based on observed ocean color. TROPOMI’s advanced imaging capabilities, including four spectrometers that measure light in the ultraviolet to shortwave infrared range, allow it to penetrate thin cloud cover and obtain ocean surface measurements more frequently.

Space advantage

The scientists said their findings demonstrate the value of using the TROPOMI alone or in conjunction with other Earth observation instruments, such as NASA’s long-running MODIS (Medium Resolution Imaging Spectroradiometer) instrument on the Aqua and Terra satellites. MODIS measures ocean color and is now used by environmental managers in Florida and elsewhere to detect algae on clear days.

Another ocean color instrument scheduled for launch in early 2024 will study 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 at a much longer wavelength than previous sensors. These observations will help predict the formation of harmful algae and the cycle of rise and fall in fisheries, as well as other factors affecting the commercial and recreational industries.

“For nearly 20 years, ocean color sensors have been the basis for satellite monitoring of harmful algal blooms,” said lead author Kelly Lewis, NASA program scientist at JPL. “This application of the TROPOMI red SIF demonstrates how the combination of satellite technologies can power early warning systems beyond the open skies.”

Satellite early warning has proven to have real benefits. A recent case study found that early detection of cyanobacteria in Lake Utah has led to significant savings in healthcare, lost work time and other economic losses. A few days’ notice can lead to quicker action on the ground, including informing the public and even closing beaches. Source