The ghastly sight of thousands of mullet, bluegill, snook, bream, and pinfish belly up and ensnared in the mangroves of the brackish lagoon on the southern tip of Siesta Key was jarring to residents, but not all that uncommon in Florida, air and water quality experts said.
It’s induced by changes in the water.
From Nov. 15 to Nov. 22, the Florida Fish and Wildlife Conservation Commission received 17 reports of fish kills from Heron Lagoon residents.
The Herald-Tribune took a water sample to experts at Mote Marine Laboratory who said they did not find the red-tide organism, Karenia brevis, or poor water salinity under a microscope. The FWC also took samples and confirmed those results.
The state wildlife agency, citing the absence of harmful algae, referred callers to the "Sarasota County Air and Water Pollution Department," which also received multiple emails and calls and sent staff to the landlocked water body to investigate the situation. They noticed discoloration to water in the lagoon and fish gasping for air at the surface of the water.
County sewer staff checked utilities in the area Nov. 15 and found the system operating as designed and no reports of sewer spills or illicit activities in the area.
A dissolved oxygen test was conducted Nov. 21 and the level measured in the lagoon was 1.36 milligrams/liter and dead fish were observed. For reference: dissolved oxygen levels below 5.0 mg/l can place aquatic life under stress. Levels under 1-2 mg/l for an extended period of time may result in fish kills, County officials said.
"It is more than likely that the lagoon had an algae bloom in recent weeks," said County spokeswoman Brianne Grant. "The recent cold snap last week and several overcast days may have contributed to the algae dying off rapidly. When algae dies off, it sinks to the bottom of the water column and begins to decay. The process by which algae decays reduces the levels of dissolved oxygen in the water. Lower levels of dissolved oxygen may lead to fish kills."
The unsightly view of the lagoon teeming with decaying fish pushed neighbors Margaret Bryant and Debbie Swoboda into action. They moved to the Heron Lagoon neighbor less than 10 years ago because of its serene beauty, recalling an undisturbed and untouched Old Florida.
A look at the fish kill at Heron Lagoon. Thousands of fish, big and small, were floating in the canal popular with for paddlesports. It’s located between Sanderling Road and Midnight pass Road on the southern tip of Siesta Key. It is not believed to be red tide related. pic.twitter.com/fRLib1HP2U
— Carlos R. Munoz (@ReadCarlos) November 21, 2019"I’ve been a little heart-sick over this because I love the lagoon out there," Bryant said. "It’s been a real joy and source of hideaway, relaxation and comfort. I’m a little sick over this whole situation."
Swoboda moved in about six years ago.
"The day we walked into the house and looked at, there were things that would require attention. But the lagoon was so attractive and serene. I had found my home and the lagoon is what did it for me."
Bryant replied, "I was stunned and blown away by how serene and beautiful it is. It’s so quiet and lovely with the natural shorelines all around. There is no motorboat noises — just birds. The water moves and flows and It has a feeling of serenity like Debbie says. We love that part of it."
For the first time since they can recall, they noticed pelicans about 10 days ago. The shorebirds were preying on easy meals floating in the water. Hundreds of vultures were nearby in the trees.
Swoboda said she had guests visiting from Alaska who alerted her to the piles of healthy looking white fish near the shore of her waterfront property.
"My heart sank," she said. "I felt sick to my stomach looking at it. It was so sad and alarming to see the fish killed off. It immediately pushed me into action."
She didn’t continue the conversation with them and called FWC, the County and Mote.
Bryant contacted Swoboda by email minutes later with the same concerns.
The two have become advocates for the lagoon and are looking to include their neighbors as part of an effort to sustain the lagoon.
"County officials couldn’t rule out that it would happen again," Swoboda said. "There may be other factors that contribute to it such as fertilizer and other nutrients. "
She is encouraging her neighbors to "self-police" and quit using fertilizers that could create the same kind of situation.
"It feels like my own personal environmental disaster," said Bryant, noting that the lagoon was unaffected by last year’s red tide. "My husband was calling Debbie and me the ’lagoon keepers.’ This might be a wake-up call in a sense. We have to step up and take citizen’s responsibility."
"We love it here."
Perfect storm
Recently, weather-related conditions have led to similar fish kills at Robinson Preserve and in two connected ponds at Palma Sola Park in Manatee County.
Craig Watson, director of the Tropical Aquaculture Laboratory at the University of Florida, said fish die-offs are more common in the summer when extreme algae blooms spring up in warm water. He said the algae doesn’t have to die to create an oxygen depletion.
"While it's producing oxygen during the day; it's using oxygen at night," said Watson about algae. "Plants actually use oxygen in the dark cycle. If you get a really heavy algal bloom you'll have really high dissolved oxygen levels in the afternoon and really low levels at midnight. You can get a fish kill without an algae die off."
The dead algae is eaten by naturally occurring bacteria that uses oxygen.
"It’s not health-issue bacteria," Watson said. "It’ bacteria that is there to eat dead things."
When the algae dies it becomes a food source for the bacteria, which blooms itself to consume the dead algae. This creates a "biological oxygen demand" — dissolved oxygen needed by aerobic biological organisms to break down organic matter (algae, fish) in the water.
Another cause of low oxygen water is turnover (stratification of the water columns) when the top of the water has high oxygen content because its in contact with the atmosphere and the lower levels are depleted. Fish will move to the surface to breathe.
"It's not a toxin, it's not a pesticide, it's not a chemical spill, it's not red tide, it's nature," said Watson, who added that aerating small water bodies is possible, but the 49-acre Heron Lagoon is too big. "It happens all the time in Florida in natural and man-made body of water. A perfect storm occurs and the oxygen is depleted from natural causes."
Storm-made lagoon
Heron Lagoon was once connected to the Gulf through Little Sarasota Pass, a waterway that was closed by a series of hurricanes from 1921 to 1947 that filled the shallow 8- to 10-foot pass with sand and closed it to the sea. It formed Midnight Pass, formerly known as "Musketeer’s Pass, on the Intracoastal Waterway bay side of the key.
Heron Lagoon is part of the Little Sarasota Watershed.
Concentrations of red tide have been found recently in the water offshore from Sanderling Road Beach. But residents who live on the lagoon did not report effects of airborne toxins often associated with a red tide bloom. Amounts of the algae were reportedly low, according to FWC samplings.
The lagoon is connected to the Gulf by stormwater pipes, creating tidal flows that causes a flushing action in the lagoon. Those pipes were "free-flowing," said David Pouso, the environmental supervisor at Sarasota County Air and Water Quality and the planning and development supervisor. He said that the algae that led to the fish kill could not be identified because it died and was consumed long before staff was able to investigate the situation.
The lagoon is expected to bounce back and fish are still present in the water.
County staff and the Florida Department of Health are continuing to monitor the water.
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‘Perfect storm’ of weather events led to fish kill in Siesta Key lagoon - Sarasota Herald-Tribune
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