Tropical Storm Debby devastated turtle nests, degraded Sarasota Bay water quality

Tropical Storm Debby significantly degraded water quality in Sarasota Bay and likely wiped out nearly half of the known sea turtle nests on area beaches, scientists at Mote Marine Laboratory and Aquarium said in a report released Thursday.

Questions also remain as to whether the immediate impacts over days to weeks will have longer-term ramifications for these ecosystems in the months and years to come. 

“Storm events like Debby can have profound effects on our coastal environments,” said Dr. Emily Hall, Manager of Mote's Ocean Acidification and Chemical and Physical Ecology Research Programs.

Mote’s initial analyses after the storm found several immediate issues, including an increase in turbidity and water color, indicating an increase in substances such as dissolved organic matter and particulate matter in the water.

Both of which were likely caused by massive amounts of stormwater resulting from the intense rainfall in the Sarasota Bay watershed. 

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Mote scientists also recorded a significant spike in concentrations of nitrate and ammonia in Sarasota Bay, that could produce algal blooms that could produce toxins harmful to marine life and potentially pose health risks to humans and pets who come into contact with the water.

Water samples also saw a drop in dissolved oxygen levels at certain sites in Sarasota Bay. Dissolved oxygen fell to dangerously low levels in North Sarasota Bay and near Stickney Point Bridge. Low oxygen levels can stress or even kill marine life, which could lead to fish die-offs and other ecological impacts.

“We are particularly concerned about the high nutrient and low dissolved oxygen concentrations, which could have serious implications for marine life in the affected areas,” Hall said.

Turtles nests wiped out

Tropical Storm Debby significantly affected sea turtle nests that were still active in the area, Mote says. 

Before the storm, Mote’s Sea Turtle Patrol had documented 4,353 nests along Sarasota County’s beaches, with 2,958 still active. 

Waves and high tides led to the over-wash and washout of many of the active nests. Scientists estimate 79% of the 2,332 still active nests were affected to some degree, with a total washout presumed on 1,231 nests — 42% of the total. 

As of the end of August, 1,131 active nests remain on the beaches, Mote's report says.

“Storm surge from the right side of the storm was the main concern for nests, according to Dr. Jake Lasala, staff scientist and program manager of Mote's Sea Turtle Conservation & Research Program.

“Debby was expected to bring 3-5 feet of storm surge and, coupled with the new moon, tidal influence would be higher,” he said in the report.

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Surge from the storm changed the beach profiles, including adding sand to some areas, meaning hatchlings would have to dig out from deeper nests. 

The report said researchers were hopeful that some of the temperature data loggers buried with the remaining research nests can be recovered, potentially providing valuable insights into the storm’s impact on incubation conditions. 

“Sea turtles have long navigated the challenges posed by natural events such as storms. Their evolutionary adaptations to these dynamic conditions are a testament to their enduring survival,” said Melissa Macksey, senior biologist and conservation manager of Mote’s Sea Turtle Conservation & Research Program.

“Tropical Storm Debby is a reminder of the ongoing need to understand and protect these remarkable creatures as they continue to adapt to their ever-changing environment.”