Red tide monitoring in the Gulf of Mexico

Florida is using several types of monitoring programs in its battle against red tide, a type of harmful algal bloom. We explore how the state’s approach to managing red tide has evolved with new technology. Today the state monitors red tide using cell counts, satellites, and water quality data, collected with Xylem’s YSI multiparameter sondes.

In 2018, the Florida red tide made global headlines, a 16-month ordeal that started around October 2017 and that didn’t subside until February 2019. Though Florida has experienced lengthier red tides, the 2018 red tide gained broader public awareness thanks to social media and an information-hungry public that wanted to understand causes and possible solutions. They also expected Florida to take action.

The causes of red tides are contentious, forcing debate about the role of climate change and industries that contribute to red-tide-stimulating nutrient runoff. But almost everyone is in agreement that Florida must protect human health, its cherished marine animals, and its tourism-based economy.

Numerous red-tide monitoring programs in Florida provide critical information to the public, policymakers and scientists. The three monitoring examples below demonstrate how these different groups can be served, and how monitoring programs have evolved.

Red tide monitoring through cell count

The Florida Fish and Wildlife Conservation Commission (FWC) publishes cell counts of Karenia brevis, the harmful marine alga, from over 100 sites along Florida’s beaches and posts them on a weekly basis. The FWC’s program of collecting water samples for cell enumeration with a microscope may seem old-fashioned to a molecularly-biased, high-tech-sensor-loving, post-millennial generation of scientists. However, microscopy remains highly valuable for a number of reasons.

First, a skilled technician can rapidly and reproducibly count K. brevis samples (not true of all algae), and the equipment is easily accessible and inexpensive. Further, there are decades of cell count data available for comparison. Florida’s HAB Monitoring Database is one of the longest, continually maintained datasets of any type, and shows that red tides have been documented in Florida as far back as 170 years. This continuity of data has been critical for demonstrating that red tides are not new to Florida, a sticky point when trying to assess red tides as natural events which at the same time can be fueled by human activity and climate change.

Monitoring with water quality data

The next level of a monitoring program incorporates water conditions that both promote and respond to K. brevis growth. Water quality monitoring potentially provides predictive capabilities as well as data that scientists use to understand biotic and abiotic factors involved in the formation and decline of a red tide. This type of monitoring need not replace cell counts, and in fact is most powerful when used in conjunction with them.

The aims of a water quality monitoring program need to be defined when choosing both the parameters and the approach to measuring them (e.g. via spot sampling or continuously-deployed multiparameter sondes), but in almost all algae bloom cases temperature, salinity, pH, dissolved oxygen and chlorophyll are useful.

Federal agencies, Florida’s Watershed Management Districts and other state agencies, private research institutions, public universities and even citizen science groups deploy a number of technologies for water quality monitoring, including YSI’s EXO and legacy 6-series multiparameter sondes. Pairing these technologies with data loggers and telemetry, the data can be made available for public consumption in near-real-time, and can also be used by researchers for incorporation into their own studies.

One such program is managed by the Ocean Research and Conservation Association, Inc., referred to as ORCA. Anyone can access ORCA’s water quality data, including historical data for the evaluation of trends and events at their monitoring sites. This data demonstrates to the public the importance of this type of monitoring not just for red tides, but also for conservation and protection of natural resources.

Red-tide monitoring with satellites

Finally, those who favor a high-tech approach will want to check out satellite-based scans that detect fluorescence from chlorophyll on the surface of the water, as well as discolored waters that are indicative of runoff from heavy rainfall events. These low-resolution but expansive snapshots from NASA’s MODIS and VIIRS satellites passing overhead provide a perspective on red tides that wasn’t possible to obtain until this millennium.

The National Oceanic and Atmospheric Administration (NOAA) has the most widely accessed satellite imaging program, and for red tides in particular one can subscribe to receive bulletins that are posted as often as twice-weekly during peak season. When integrated with cell counts, water quality data, and wind and other meteorological data, the satellite data form the foundation of fairly sophisticated forecasting models for not only red tides but also other types of algal blooms. NOAA’s Harmful Algal Blooms Observing System (HABSOS) is an example of bringing all of that information together for environmental managers, scientists, and the public.

An inconvenient limitation of satellite monitoring is that cloud cover can obscure the satellite’s view of the water. It is during these periods of high cloud obfuscation that it becomes apparent why the pairing of the satellite imagery with the cell count information is highly valuable. The cell counts must be relied upon for filling in the gaps created by the cloud cover. Of course, cell counts can’t cover the wide geographical range that the satellites can, and that information paired with the wind and current data, is important for understanding what may yet be coming to the shores of Florida.

Read more in Mission: Water magazine

Written by Dr. Stephanie A. Smith