Lizcano-Sandoval et al. 2023. Seagrass Areal Cover in Tampa Bay over the Last 30 Years (1990- 2021) Observed by Satellites

Lizcano-Sandoval, Luis, Daniel Otis, Enrique Montes, and Frank Muller-Karger. 2023. “Seagrass Areal Cover in Tampa Bay over the Last 30 Years (1990- 2021) Observed by Satellites.” Florida Scientist 86:331–38.

Seagrasses in Tampa Bay are a fundamental habitat that is central to the research and management efforts of the Tampa Bay Estuary Program and the Tampa Bay community in general. Improving and sustaining good water quality (as measured by reduced chlorophyll concentrations and nutrient inputs over time) is an important goal to enable a continued increase in areal cover and density of seagrasses in the bay. In order to track success, assessments of seagrass areal cover are conducted by aerial mapping every two years during months of high-water clarity, typically in January-May. Satellite imagery is an available tool that allows for continuous seagrass monitoring, but which has not been used routinely due to uncertainties and complications of understanding the optics of the water column. Imaging of estuarine waters for benthic cover assessments is challenging due to changes in water clarity, sunglint effects, and depth. We developed algorithms for selecting and processing large imagery collections from the Landsat and Sentinel missions for detecting and quantifying seagrass areal cover change over time. The ability to process large amounts of data was facilitated by using Google Earth Engine and the Python programming language. We used Landsat 5, 7 and 8 from 1990 to 2015, and Sentinel-from 2016 to 2021. Sentinel-2 provided a higher number of images per year. We detected decreases in seagrass areal cover in 1990-2000 and increases in 2000-2021. Overall, seagrass area increased from 70.6 km 2 to 96.9 km 2 in the three decades since 1990 to 2021. These trends match the aerial mapping done by the Southwest Florida Water Management District (SWFWMD). The long-term trends in seagrass areal cover match the trend toward improving water quality in Tampa Bay. Further development of tools in the cloud can help managers and scientists understand dynamics of seagrasses and other coastal ecosystems.