Microscopic analysis of water samples is a common way to assess the abundance of red tide and is the source of data shown on the coastal Water Atlas websites. During this process, Karenia brevis cells are counted in a known water volume, a concentration is calculated, and reported as number of cells per liter. Cell counts are a widely used and mature technique that is approved by the Food and Drug Administration (FDA) for closure of commercial shellfishing operations.
The process of counting the cells was once manual and laborius, but many scientists now use a NASA-funded cellphone microscope app, the ‘HABscope,’ that can, within minutes, analyze the concentration of cells of the red tide organism in a water sample.
Water quality monitors place drops of water onto a microscope slide and take a video of the sample. Once they file the video of the sample, the app calculates the cells per liter, which in turn determines the level of red tide in the water. The app has an algorithm that can identify K. brevis based on its swimming pattern.
There are several other ways to measure red tide. Using bioassays of shellfish tissue is the FDA-approved method for reopening shellfish beds closed because of red tide. Other techniques involve satellites, genetic probes, and various optical methods.
A sampling network is coordinated by the Fish and Wildlife Research Institute (FWRI) that involves volunteers and professionals and includes the Florida Fish and Wildlife Conservation Commission, Mote Marine Laboratory, Florida Department of Agriculture and Consumer Services, Rookery Bay National Estuarine Research Reserve, and the health departments of Sarasota, Lee and Collier Counties. More information about this effort is available online at https://myfwc.com/research/redtide/statewide/.