'Big blob' in Gulf waters off Sanibel likely harmless

The News-Press

Rick Bartleson, a water quality scientist for the Sanibel Captiva Conservation Foundation uses a drag net that catches microscopic organisms. The Sanibel Captiva Conservation Foundation was testing the water off of Sanibel after seeing photos of a blob from aeriels. Bartleson tested the samples and it turned out to be diatoms which are non harmful.

A milky-white patch of water off Sanibel Island is likely a harmless combination of microscopic critters and churned up waters.

That's the analysis from a local water quality scientist who monitors various conditions and reports them to local and state government agencies.

Some had feared it was a bloom of trichodesmium, or sea sawdust, which is a precursor, at times, to red tide outbreaks.

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"Trichodesmium can add nitrogen to an area, so the red tide gets everything it needs to get going," said Rick Bartleson, with the Sanibel-Captiva Conservation Foundation. "We always get a trichodesmium bloom before we get a red tide, but we don't always get a red tide when we have trichodesmium."

Red tide, or Karenia brevis, is a harmful algal bloom that causes fish and marine mammal kills, respiratory issues in humans and causes swimming beach closures.

The National Oceanic and Atmospheric Administration posted maps recently that showed elevated chlorophyll A levels, a sign of a possible algae outbreak.

"They got a pretty good pattern from here to Marco," Bartleson said." And not just to the south, it goes north too."

Rick Bartleson and Eric Milbrandt from Sanibel Captiva Conservation Foundation prepare to test the waters off Sanibel on Tuesday. They were reacting to reports of an unknown blob that was documented by water quality advocates. It was determined that the blob was diatoms, which are naturally occuring and non harmful.

Some water quality samples taken Friday off Sanibel beaches showed signs of trichodesmium, but Bartleson and other researchers haven't found any indications of a bloom.

Photos submitted by Calusa Waterkeeper to The News-Press earlier this week showed discolored waters at the south end of the island and extending offshore.

"Trich(odesmium) is a marine cyano(bacteria) so we're happy that it's not that," said John Cassani, with Calusa Waterkeeper.

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The Sanibel-Captiva Conservation Foundation has several water quality testing sites and sensors in San Carlos Bay and around the mouth of the Caloosahatchee and upstream in the freshwater portions of the river.

But there are no offshore water quality sampling sites here.

Bartleson and Eric Milbrandt, director of the conservation foundation, tested two sites Tuesday, one nearly two miles offshore of Sanibel and another about a mile offshore of the island.

"It looks like calcium carbonate that's been stirred up," Milbrandt said as the boat bobbed up and down in the Gulf of Mexico. "The bottom is made mostly of shells, and the shells basically break up into dust."

Calcium carbonate can cause Gulf of Mexico water to look milky-white.

Rick Bartleson, a water quality scientist for Sanibel Captiva Conservation Foundation points an area where a blob was documented off of Sanibel Island over the last several days. After some tests, Bartleson determined they were diatoms which are occur commonly and are not harmful.

Cassani said water quality issues like these should be looked at more comprehensively to understand exactly what natural conditions are, so that those baselines can be compared to current and future events.

"What keeps these extreme population swings from occurring is limiting the huge nutrient loads," Cassani said. "Are we artificially promoting these blooms by making more iron and phosphorus available to them?"

Connect with this reporter: Chad Gillis on Facebook.