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Tampa Bay seagrass declines for the third consecutive mapping assessment

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Seagrass coverage in Old Tampa Bay is at an all-time historic low.

TAMPA BAY – Mapping results released by the Southwest Florida Water Management District (SWFWMD) show that Tampa Bay now harbors 30,137 acres of seagrass. Between 2020 and 2022, seagrasses throughout Tampa Bay declined by 12%, or 4,161 acres. This is the first time Tampa Bay has experienced seagrass losses for three consecutive mapping assessment periods between 2016 to 2022.

The majority of those losses occurred in the upper portions of the bay, which are more sensitive to freshwater inflow from rivers and stormwater runoff. Old Tampa Bay and Hillsborough Bay were down 2,518 acres (38%) and 428 acres (51%), respectively. Bay managers have expressed concerns about recurring summertime algae blooms and water clarity trends affecting seagrass in Old Tampa Bay for several years. Now, seagrass coverage in Old Tampa Bay is at an all-time historic low. Research focused on additional seagrass stressors, such as warming water temperatures and obstructions to tidal circulation in Old Tampa Bay, are underway and guiding restoration efforts.

Recent seagrass acreage estimates are based on imagery collected during the winter of 2021-2022, after the emergency discharges from Piney Point and subsequent red tide bloom but prior to the passage of Hurricane Ian. Notably, losses in Middle Tampa Bay were concentrated along the southeastern shore from Bishop Harbor to Apollo Beach, an area of particular interest for the coordinated environmental monitoring response following the Piney Point event.

The aerial surveys used to estimate seagrass coverage are coordinated by scientists at the SWFWMD. Aerial photos are taken every two years in the 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. The Tampa Bay Estuary Program (TBEP) also coordinates a monitoring program that tracks changes in seagrass species, health, and abundance to complement the SWFWMD mapping program.

Historically, seagrass recovery in Tampa Bay has been linked to reduced nutrient pollution and associated improvements in water quality. Long-term nutrient loading to Tampa Bay continues to decline, but these recent setbacks demonstrate the need to better manage both nutrient sources and additional stressors that might be affecting seagrass resources. In 2022, water quality targets were met for all bay segments, indicating that bay waters were clear enough to support seagrass growth. “I’m hopeful that this is the beginning of a corrected course for Tampa Bay,” said TBEP Executive Director Ed Sherwood. “Now, we need to string together several good years of improved water quality to jumpstart seagrass recovery and get Tampa Bay back on track.”