SWFWMD preview: Tampa Bay seagrass maps due March 26; Old Tampa Bay remains concern

Dr. Chris Anastasio, chief water quality scientist and seagrass mapping lead at the Southwest Florida Water Management District, told the Hillsborough County Environmental Protection Commission on Feb. 20 that draft 2024 seagrass maps for the Suncoast region will be released publicly on March 26 and that overall Bay‑wide conditions are expected to be better than the 2022 maps.

The maps, which the district has produced regularly since the 1980s, use specialized aerial imagery combined with field verification to classify seagrass as continuous (roughly 25–100% cover) or patchy/sparse (less than 25%). "Now, unfortunately, our official numbers don't come out for about another month," Anastasio said, but he previewed the district's expectations and the methods behind the mapping program.

Why this matters: seagrasses are a key indicator of estuary health, provide fish and wildlife habitat, and support recreation and tourism that local economies depend on. The district's mapping program informs restoration priorities and coordination through the Tampa Bay Estuary Program and related management efforts.

Anastasio summarized the mapping process and the limits of aerial detection. Imagery is collected from aircraft during preferred flight windows (roughly Dec. 1–Feb.), then post‑processed and photo‑interpreted. Field verification — roughly 2,000 points for the Suncoast region in the previous cycle — is used to ground‑truth the imagery. He cautioned that the program's practical detection limits mean small, very sparse patches (below ~10% cover) often are not visible from aerial imagery; as a result the maps provide conservative estimates of spatial extent.

The district divides its coverage into two program regions: the Suncoast estuaries (Clearwater Harbor through Charlotte Harbor, including Tampa Bay) and the Springs Coast (northwest Gulf rivers and Big Bend area). Anastasio noted the Springs Coast remains relatively stable; the 2020 mapping identified roughly 586,000 acres of seagrass in that region and showed little change since 2016.

For Tampa Bay, Anastasio recapped the 2022 result that showed about a 12% Bay‑wide loss and said Old Tampa Bay has been the segment with repeated declines since about 2016–2018. "We still are gonna see some loss in Old Tampa Bay in '24, but the good news is it's the only segment in Tampa Bay where we will see loss in '24," he said. In contrast, he said draft 2024 results should show Hillsborough Bay improving substantially compared with 2022; much of that gain, he added, is expected to be sparse coverage rather than dense meadow.

Commissioners and staff pressed for context. Commissioner Wolstow asked whether seagrass can help filter pharmaceuticals from reclaimed water; Anastasio said he was not aware of much research specifically on pharmaceuticals and seagrass but noted seagrasses can act as bioremediators for some contaminants and that the question merits further study. Commissioner Cohen asked how to interpret changes beyond the program's minimum detection limits; Anastasio explained that small year‑to‑year changes can be noise, while multi‑year or repeated losses trigger management responses.

Anastasio pointed commissioners to public data and tools: the district's open data portal (which hosts seagrass maps back to 1988 where available) and a web tool that allows side‑by‑side comparison of maps and imagery from 1999 forward (recommended for use in Google Chrome). He also said the Tampa Bay Estuary Program and the Nitrogen Management Consortium coordinate follow‑up and management work where maps indicate problems.

The district will present the draft 2024 numbers at the Seagrass Working Group meeting coordinated by the Tampa Bay Estuary Program at FWRI's Steidinger Auditorium on March 26 (public meeting; morning session). The Springs Coast 2024 numbers are expected later in spring, probably May.

Anastasio closed by noting the mapping program is continuous and resource managers use the maps as a diagnostic: "think of our seagrass maps more like, when you go to the doctor and they take your blood pressure," he said, meaning repeated declines prompt targeted investigation and mitigation.

The commission thanked Anastasio for the briefing and invited continued coordination through the Estuary Program and local monitoring partners.