Sea Grass Decline on Tampa Bay After Years of Increase

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Sea Grass Decline on Tampa Bay After Years of Increase

Tampa Bay, FL: Provisional results released earlier this month by the Southwest Florida Water Management District (SWFWMD) show that Tampa Bay now harbors 35,240 acres of seagrass. Between 2018 and 2020, seagrasses throughout Tampa Bay declined by 13%, or 5,411 acres. The majority of those losses occurred in Old Tampa Bay, which was down 3,200 acres. Losses were also reported in Hillsborough Bay (-525 acres) and the Manatee River (-150 acres). Lower Tampa Bay reported little to no change in mapped seagrass acreage. These estimates are based on imagery collected during the winter of 2019-2020, before the emergency discharges from Piney Point began in spring 2021.

The surveys used to estimate seagrass acreages are coordinated by scientists with the SWFWMD. Aerial photos are taken every two years in winter, when bay waters are clearest. The digital imagery is plotted, analyzed and ground-truthed to verify accuracy. SWFWMD has used this comprehensive process to track trends in seagrass extent in Florida estuaries since 1988.

To complement the aerial surveys, the Tampa Bay Estuary Program (TBEP) coordinates a monitoring program that further describes the bay’s seagrass resources. An interactive dashboard tracks changes in seagrass species, health, and abundance. In Old Tampa Bay, bay managers have been concerned about recurring summertime algae blooms and water clarity trends for several years. There, on-the-ground assessments show that rooted macroalgae (Caulerpa prolifera) are replacing seagrasses.

Tampa Bay has come a long way since the early 1980s, when the SWFWMD mapped a mere 21,653 acres of seagrass in the bay. Much of the bay’s environmental recovery came as a result of persistent efforts to control nutrient pollution. Those investments paid off after the bay reached a record high of 41,655 acres of seagrass habitat in 2016. As a result, TBEP’s Habitat Master Plan (2020 Update) established a new restoration goal for seagrass: maintaining at least 40,000 acres of seagrass within Tampa Bay. “We know that the bay can support extensive seagrass meadows,” noted TBEP Ecologist Gary Raulerson. “This represents a slight increase from the previous goal of 38,000 acres. The new goal is intended to protect the progress we’ve already made and is consistent with the community’s history of setting ambitious goals.”

This year’s results are a clarion call for bay managers. Seagrasses are important because they are essential fish nursery habitats. They are a major food source for marine wildlife, including manatees and sea turtles. They also trap sediments, improve water clarity, and offset the impacts of climate change. Improving water quality for the benefit of increasing seagrass coverage in Tampa Bay has been a hallmark achievement of the TBEP, which celebrates its 30th

anniversary this year. TBEP and its partners are committed to investigating and addressing the complex causes of the observed 2020 declines in seagrass resources in Tampa Bay.