Red Tide and Nutrient Study Advancing at Mote

Our friends at Mote Laboratory have asked us to share the following news release:

Mote Marine Laboratory scientists are studying samples from the current bloom of Florida red tide this week in Southwest Florida to advance a major research initiative: learning how nutrients in the water play into the complex “recipe” for red tide.

Florida red tide is a bloom, or intense concentration, of the harmful alga Karenia brevis that occurs naturally in the Gulf of Mexico. These microscopic plant-like organisms, or phytoplankton, produce brevetoxins that can kill fish and other marine life and cause respiratory irritation and illness among humans — especially those with asthma or other chronic respiratory conditions. Red tides usually begin 10-40 miles offshore, and their effects may go unnoticed until they are carried near the coast by winds and currents.

Mote scientists and colleagues have worked for decades to understand how Florida red tides develop, change and dissipate, but science has not fully revealed what triggers the beginning of a Florida red tide — a mix of biology, chemistry and physics that appears to be different for each bloom. A major complication is that other microscopic algae can compete against K. brevis for nutrients (food).

Nutrients can come from many natural and manmade sources. Red tide blooms offshore might start with help from nutrients released from sediments or from upwellings — ocean circulation patterns that bring nutrient-rich water up from the bottom. Red tide blooms carried to shore might strengthen with nutrients flowing off the land, including nutrients from plant and animal materials in nature and manmade sources such as fertilizers. Red tides likely even free up nutrients when they kill fish, which are rich in nitrogen and other nutrients. However, if other microscopic algae consume these nutrients first, their presence might hinder or even help red tide algae.

Since 2007, Mote has conducted 11 bioassays to better understand how microscopic algae respond to nutrients. These field studies involve collecting water samples from Southwest Florida containing the many naturally present varieties of microalgae, and then growing those algae in containers “spiked” with combinations of nutrients. The researchers also grow the algae in containers with water from estuaries, where nutrients can be washed from land to the sea. Results to date have shown that algae other than K. brevis usually dominate in the competition for nutrients, and these algae might show different responses to nutrients depending on the time of year and other factors — but algae were especially likely to grow and proliferate with added nitrogen.

Until now, the bioassays for this study contained too few red tide cells for scientists to learn much from their growth. The current bloom has allowed Mote scientists to add the critical missing piece.

“This is an opportunity to use a moderate natural bloom of red tide algae and look closely at the response to added nutrients and combinations of nutrients,” said Dr. L. Kellie Dixon, manager of Mote’s Chemical and Physical Ecology Program. “We have already made some interesting discoveries about the algal community in general, and these findings have provided important context for understanding red tide, but the real keystone of this project is using a naturally occurring Karenia brevis bloom directly — and including the other algae that are present in the bloom and appear to compete for nutrients with K. brevis.”

Mote scientists collected water samples from the bloom by boat on Tuesday, Oct. 23. On Monday they collected water samples from the three estuaries — Tampa Bay, Charlotte Harbor and the outlet of the Caloosahatchee River — areas that normally have more nutrients than the offshore waters where the bloom developed. They added this estuarine water to some samples of the bloom, left some samples alone and spiked other samples with specific nutrients and nutrient combinations. Each sample is being grown for two days and subsamples are collected daily for analysis. Analyzing all the samples and assembling all the data in a comprehensive evaluation could take up to six months.

“We want to know how red tide algae respond to nitrogen, phosphorous, silica and other substances found along our coast, and learn how other types of algae might compete with or affect the red tide organism,” said Dr. Gary Kirkpatrick, Manager of Mote’s Phytoplankton Ecology Program.

Said Dixon: “There seem to be many paths to starting a Florida red tide, and many things that could prolong or hinder it. The more direct evidence we can find, the better we can understand these dynamics and communicate that information to our state and national resource managers. That’s the key to responding to these blooms and providing the public with accurate information about them.”

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