A tiny sea worm could be a gateway for human exposure to neurotoxin

Jul 12, 2018

Humans could consume a neurotoxin produced by algae through a food chain of creatures that begins with a tiny sea worm, according to a study published last week by a Louisiana researcher. While it has been well established that humans can ingest the toxin through shellfish, the new study provides evidence that humans could also be exposed to the toxin by eating other contaminated seafood.

The neurotoxin, domoic acid, is produced by some species of microscopic algae and has been found in the coastal waters of the Gulf of Mexico. No cases of illness have been reported from eating seafood contaminated with the toxin from the Gulf. Still, there is evidence the algae that produces the toxin is becoming more common as a result of water pollution, according to the National Oceanic and Atmospheric Administration.

Algal blooms typically form off the coast of Louisiana in the spring and summer, as fertilizers and other pollutants carried by the Mississippi River pour into the Gulf. These fertilizers, especially nitrogen, spur algae growth. Some of these algae produce domoic acid.

When this toxic algae sinks to the water bottom, it is eaten by tiny worms, called fringe-gill mudworms or paraprionospio pinnata. Colonies of bacteria also consume the algae on the seafloor. As they do so, they can deplete oxygen in the water causing hypoxia.

But the mudworms have adapted to living in hypoxic water, said Melissa Baustian, a coastal ecologist with the Water Institute of the Gulf and the lead author of the new study. The worms have gill-like structures on their heads that help them capture oxygen in the water. Because of their ability to survive low oxygen, the worms are abundant on the continental shelf, she said.

Baustian collected some of these worms with a sampling device rigged from a research vessel. The device, which looks like a metal box, was sent down to the water bottom where it scooped up mud from the seafloor. She then dissolved the worms she collected in acid to see the contents of their guts.

Inside the worms, she detected the domoic acid producing algae. Brown shrimp, blue crabs and Atlantic croaker are all known to eat these worms. Thus, they could potentially consume the toxin.

"We tend to not think about the sea floor when we hear about harmful algal blooms," she said. "This linkage to the sea floor could be really important, especially because we have this really important shrimp industry off our coast."