Video is provided courtesy of Florida Atlantic University
Researchers are studying the relationship between bioluminescence and toxin production in the Indian River Lagoon, hoping to better understand how the microscopic organisms behind the lagoon’s summer light displays grow and form blooms.
A newly published study examines Pyrodinium bahamense, a bioluminescent organism that produces the neurotoxin saxitoxin and forms recurring blooms in the lagoon.
A newly published study examines Pyrodinium bahamense, a bioluminescent organism that produces the neurotoxin saxitoxin and forms recurring blooms in the lagoon.
Dr. Kathleen Cusick, a researcher with FAU Harbor Branch, said the organism combines two characteristics that make it particularly interesting to scientists studying harmful algal blooms.
"I like to refer to Pyrodinium as the Reese's Peanut Butter Cup of dinoflagellates that form these harmful algal blooms, right? Reese's Peanut Butter Cups, best of both things, chocolate and peanut butter. And Pyrodinium has my two favorite features, bioluminescence and toxicity," she said.
Cusick's research examines why the organisms maintain both traits, which require energy to produce, and how they might influence the development of blooms.
"Both toxin production and bioluminescence are very expensive energetically for the cells, right? They require a lot of effort to produce. And so why maintain both?" she said.
The question has implications for the lagoon's health. Saxitoxin, the neurotoxin produced by P. bahamense, can affect organisms exposed to it, while large blooms can also block sunlight from reaching seagrass.
"It's a potent neurotoxin. And so any higher organism that is feeding on these cells or around these cells, they can get a large dose of the toxin. And so it can affect it at the ecosystem level. That's with toxicity," she said. "These blooms in general can affect the health of the lagoon because you get massive growth of these cells and then they cut off the sunlight. So then the seagrass isn't getting the sunlight in order for it to grow."
One finding could eventually give researchers another tool for assessing bloom toxicity. The study found a positive correlation between the activity of a gene associated with toxin production and the amount of toxin produced. The finding suggests that measuring the gene's activity could help scientists monitor the toxicity of these populations.
"We found a positive correlation with the amount of toxin that was being produced and the level of activity of this gene. And so we can use it as a molecular marker for monitoring the lagoon and the toxicity of these populations," Cusick said.
The research also found an inverse relationship between population size and the amount of toxin produced per cell. In laboratory experiments, strains that produced more toxin grew more slowly than those producing less.
Cusick said that relationship could help explain how blooms expand, although scientists are still working to understand the connection between toxicity and bioluminescence.
"As I said, toxicity and bioluminescence are both very energetically expensive. So as the population grows, some of them may decrease their toxicity, but retain their bioluminescence because their predators now stay away from them because that is toxic. Dropping that toxicity, not making as much, not producing it at all, is going to enable the cell to grow faster," she said. "Because these are single-celled organisms and they're dividing and that's how they are expanding the population."
The study's authors propose that bioluminescence may help protect the organisms from predators, potentially allowing some strains to produce less toxin and grow more quickly while retaining their ability to glow.
Understanding what triggers the blooms is another part of the puzzle.
"We know that part of it is based on temperature. They disappear during the winter months usually because it's colder. And then we have different monitoring systems out there in the lagoon that are measuring different water quality parameters. And so we can link these with the different water quality parameters to try and get a sense of what is driving these blooms," Cusick said.
She also wants to better understand how nutrients entering the lagoon affect bloom growth and toxicity. Nitrogen and phosphorus are essential nutrients for these organisms, much as fertilizer supports plant growth.
"There's a lot of nitrogen going into the lagoon right now. Where is it coming from? What form is it in? Same with phosphorus. Those are the two key things, right? These dinoflagellates, they're like little plants. And so nitrogen and phosphorus are like fertilizer for them," she said. "Give them a lot, they're going to grow a lot."