Toxic algae impact extends far beyond just the surface waters

BATON ROUGE, La. (July 31, 2018) – The impact of toxic algae blooms run much deeper, literally, than the green, brown, or red smelly sludge people witness causing so many problems along the beaches and marinas of the northern Gulf of Mexico.

Deep below the surface, along the floor of the Gulf of Mexico there is a largely unseen process going on in which toxin-producing algae are consumed by tiny marine worms giving the toxic domoic acid in the algae a gateway into the larger food web, according to a new report out in “Harmful Algae.”

“We tend not to think about the sea floor when we talk about algal blooms,” said Melissa Baustian, lead author of the article and coastal ecologist at The Water Institute of the Gulf. “This linkage to the sea floor could be really important.”

The domoic acid toxin is produced by particular algae – in this case Pseudo-nitzschia – which forms in the spring as the nutrient rich waters flow down the Mississippi River and into the Gulf of Mexico. This nutrient plume stimulates the production of algae which is either consumed or dies and falls to Gulf of Mexico sea floor. It’s here that tiny marine worms feed on the algae that could contain toxic domoic acid, and the worms in turn become food for higher organisms such as the Atlantic croaker – itself a food source for many species in the Gulf of Mexico.

“There are some fish that directly feed on algae. We were interested if there was a second route,” Baustian said.

Baustian and her colleagues from Louisiana State University, Louisiana Universities Marine Consortium, and University of Georgia confirmed this connection by reexamining worms collected and preserved in 2003 and 2004 and analyzed the gut contents of worms and found those algae that are known to produce domoic acid. These same researchers have shown that these tiny worms are in the diet of the abundant Atlantic croaker.

“That’s why we think these worms could be the connector between toxic algae and the rest of the food web,” Baustian said.

Although first reported in the 1960s in the Netherlands, increased interest in tracking the routes the toxic domoic acid takes to get into the food web was really stirred after a 1987 outbreak in Prince Edward Island, Canada. Three deaths and more than 100 illnesses were caused by the consumption of cultivated blue mussels that were contaminated by this toxin from one bay in the region. In that case, it was the blue mussel that provided the connection between toxins in the algae and the food chain so Baustian said they wanted to see if there was a similar connection somewhere in the northern Gulf of Mexico.

Although algal blooms are the precursor to the annual dead zone in the Gulf of Mexico off the coast of Louisiana, several factors allow the worms to survive and for predators to eat them. First, this particular worm is very adaptable to low oxygen levels so even after other animals die or move away, the worm can survive. In addition, there’s a time lapse of a couple months between when the worms are feeding on the algae and the low-oxygen area of dead zone forms, giving ample time for the toxin in the worms to have made its way into the food chain. Accumulation of this toxin in animals has been citied as the cause for numerous fish and wildlife die-offs including sea lions on the west coast and outbreaks of human illnesses around the world from Chile, to Europe, to Japan.

“This is another route for toxic algae to impact the northern Gulf of Mexico food web and is something that future research needs to take into account when looking at impacts of nutrients and harmful algal blooms,” Baustian said.

Link to the article is here.