Tampa Bay loses 6,350 acres of seagrass over past two years

The amount of healthy seagrass in Tampa Bay is lower than previously estimated.

Thursday, a Southwest Florida Water Management District official said Tampa Bay had seen a 16 percent decline in seagrass, or more than 6,350 acres, over two years ending in 2020. That’s higher than estimates released in April that measured a 13 percent drop.

“That sends up an alarm that something is going on that we need to pay attention to,” said Chris Anastasiou, chief scientist of the water district’s surface water improvement and management program.

His comments came Thursday during a presentation to the Hillsborough County commissioners sitting as the Environmental Protection Commission.

The numbers released in April were provisional, Susanna Martinez Tarokh, a spokeswoman for the water management district, told the Times. The amount of lost seagrass was revised upward after field verification work in Old Tampa Bay and Hillsborough Bay, she said.

Related: Tampa Bay lost 13 percent of its seagrass

The final mapping data showed seagrass acres declined from 40,651 in 2018 to 34,298 in 2020 according to measurements taken from the Manatee River north to Old Tampa Bay.

The decline is a regional phenomenon that extends beyond Tampa Bay, said Anastasiou. The number of seagrass acres dropped 18 percent in Sarasota Bay and 23 percent in Charlotte Harbor during the same two-year period. The numbers in Clearwater Harbor, however, were virtually unchanged.

The decline in Tampa Bay seagrass follows a smaller drop documented in 2018. Prior to that, the biennial measurements had shown expanding seagrass beds since 1999.

“It’s disturbing and concerning to hear this now,” said Hillsborough Commissioner Pat Kemp.

Anastasiou declined to offer a specific cause for the lost seagrass, but noted the problem was worse as the distance up the bay from the open Gulf of Mexico increased. Water circulation in the bay and heavier rainfall that can bring nutrient discharges into the water are among the suspected contributors.

Seagrass supports clearer water, feeds animals such as manatees and turtles and acts as a nursery for fish. As much as 50 percent of commercial and recreationally important fish spend a portion of their lives in seagrass beds, Anastasiou said.

It also helps trap carbon, forming a natural defense with marshes and wetlands against emissions that worsen climate change.

“It’s a big deal,” Commissioner Mariella Smith said about the declining acreage.

The vegetation, Anastasiou said, can be construed as the canary in the coal mine because it is “an excellent barometer of how an estuary is doing.”

So, what should we be doing? asked Commissioner Harry Cohen.

Commissioners are poised to consider a proposed ordinance from Smith in the coming weeks to regulate residential landscape fertilizer use during the rainy season. The goal is to eliminate excessive nutrients from running into the bay that could feed algae blooms.

“Shame on us,” said Cohen, “if we don’t pay attention to these signs and we don’t do something before the damage is irreversible.”

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