For the last several months, Southern California has grappled with a bloom of harmful algae that produce domoic acid, killing or intoxicating thousands of marine animals. But this region isn't unique. Problematic outbreaks of DA, a naturally occurring amino acid that's also a potent neurotoxin, are becoming increasingly common along both the West and East coasts.
DA can enter the food web when it is consumed by filter feeders like mussels and then accumulates up in marine predators. When DA intoxicates "keystone" species, which play an outsized role in maintaining local biodiversity, it can have cascading consequences for all the animals around them.
While the impacts of DA on marine vertebrates are well-documented, its effects on marine invertebrates — those without backbones — have received less attention. A new study in Diseases of Aquatic Organisms , led by researchers at Bigelow Laboratory for Ocean Sciences, fills this gap by examining whether DA accumulates in wild sea stars and if it has any behavioral or physiological impacts.
The team found potentially concerning concentrations of DA, particularly in smaller sea stars, even in the absence of the algal blooms that are thought to drive DA outbreaks. When experimentally exposing the animals to kainic acid, a structurally similar compound, the researchers also saw an immediate physical response. Though those behavioral changes appear to be reversible, the findings raise concerns about the potential consequences of repeated, long-term, or higher-level exposure on sea stars.
"Some species of sea stars are the keystone species of the intertidal zone, and we know if domoic acid is harming them, other animals down the line could be affected," said the study's lead author, Dennie Truong, a recent Colby College graduate and former Bigelow Laboratory intern. "There's very little information out there on domoic acid in sea stars, so this was a critical first step to understanding the dynamics of DA intoxication."
DA is produced by over 20 different species of single-celled algae in the genus Pseudo-nitzschia, and it can have significant health effects — including on humans that eat contaminated seafood. Despite the risk, and the ecological importance of sea stars, little work has been done to determine what concentration of DA is toxic to them.
"Sea stars aren't a human food source or commercially valuable, but they're fascinating biologically and vital ecologically," said Research Scientist Reyn Yoshioka, a co-author on the paper. "Understanding how DA may be present in and affect diverse species is key to us holistically understanding the impacts of marine biotoxins."
In 2022, while Truong was a participant in Bigelow Laboratory's Sea Change Semester, he worked in the lab of Senior Research Scientist Maya Groner, with Yoshioka and former Research Associate Carmen Cartisano, to measure the concentrations of DA in sea stars from Strawberry Hill in Oregon and Lamoine State Park in Maine.
The researchers detected levels of DA in the sea stars similar to the known toxicity levels for other marine animals, despite there being no evidence of recent Pseudo-nitzschia blooms. They also found that the compound was most concentrated in the pyloric caeca, an organ that is critical to sea star digestion and energy storage.
The researchers then undertook experiments to better understand the potential effects of this exposure.
For seven days, they held sea stars in tanks in Bigelow Laboratory's seawater suite, which continuously pumps in aerated seawater directly from the ocean. The sea stars were injected with kainic acid at different concentrations to reflect what they might experience in the wild.
For the animals in the "high dosage" group, the effects were almost immediate. "They just curled right up into a ball," Truong said. The vast majority lost the ability to right themselves when flipped on their backs, and many had deflated arms.
These behavioral changes did eventually wear off — within a few days for righting time and a week for arm circumference. But the nature and immediacy of the reactions, the authors argue, are concerning. It suggests that kainic acid may be disrupting the mutable collagenous tissue, which is vital for sea star movement and structural integrity.
These findings, Truong said, provide the first evidence of how — and how much — DA affects sea stars, which is the first step to understanding its ecological consequences. In the future, the team wants to confirm that DA has the same experimental effect as kainic acid and dig into the relationship they observed between body size and DA accumulation, and what that might mean for different sea stars' ability to handle toxins.
"We have seen substantial declines in sea stars in the past decade attributed to changes in mussel abundance and sea star wasting syndrome, but this work suggests that harmful algal blooms may also be a problem for them," said Groner, the paper's senior author. "As these harmful algal blooms that produce domoic acid become increasingly common, it's important that we understand their impacts on keystone species, marine food webs, and biodiversity."
