Pinniped Problems: Domoic Acid Diatom Denotes Death

Jackson Eberwein, Sonoma State University

The Problem: Imagine a new disease spreading through your community, and it is deadly. It injures the kidneys, affects heart muscles, and causes parts of the brain to wither away. Scientists and doctors know that it is caused by a toxin made by a microscopic organism that loves to suddenly appear with force in unpredictable restaurants across the country. Despite this knowledge, doctors have no good way of knowing that a person has the disease until it is too late.
This is the reality for California sea lions. Along the west coast, large blooms of algae have been producing a toxin called domoic acid, and sea lions have been getting stomachs full of it through their diet of alga-eating fish. According to California Marine Mammal Stranding Network records from 1998 to 2006, around one out of every four California sea lion beach strandings or deaths along most of the California coast were due to exposure to the biotoxin. Since 2006, blooms of the algae have increased, with stranding numbers rising along with them.

California Sea Lion (Zalophus californianus) spooked about eating bad fish.
Photograph by Pixiabay

No good blood test exists for Domoic Acid Toxicosis, as the biotoxin that causes it rapidly clears from the body of sea lions. This means veterinarians can’t see if a sea lion has it unless they use outdated or expensive tests, or guess based on how an animal acts. Since veterinarians don’t have a good way to measure how bad the disease is, they don’t really know for sure if what they do helps a sick sea lion. If they wait to use the behavior of the animal to judge, then it is already too late because the disease has done permanent damage.
So how do we get a viable blood test? Can something be measured in blood when it is simply not there? In this case, we think it can, though not directly. While the domoic acid is in the body, it will be doing what toxins do best: messing with a lot of things that should not be messed with. This will cause changes in the body, such as more or less of a protein being made than it usually is. An unusual change in production of a protein could be measured instead of the toxin that caused that change. In this situation, the protein is called a “biomarker”, or a proxy for measuring the real target. By finding a biomarker protein in sea lion blood, it will actually be possible to make a cheap and effective blood test for the impacts of domoic acid!

Acknowledgements

I would like to thank Dr. Michael Janech, Dr. Benjamin Neely, Alison Bland, The Marine Mammal Center, & College of Charleston. Supported in part by the Fort Johnson REU Program, NSF DBI-1757899.

Neely BA, Ferrante JA, Chaves JM, Soper JL, Almeida JS, Arthur JM, et al. (2015) Proteomic Analysis of Plasma from California Sea Lions (Zalophus californianus) Reveals Apolipoprotein E as a Candidate Biomarker of Chronic Domoic Acid Toxicosis. PLoScONE 10(4): e0123295. doi:10.1371/ journal.pone.0123295

Bejarano, A.C., Gulland, F.M., Goldstein, T., Leger, J.S., Hunter, M.S., Schwacke, L.H., VanDolah, F.M., & Rowles, T.K. (2008). Demographics and Spatio-Temporal Signature of the Biotoxin Domoic Acid in California Sea Lion ( Zalophus californianus ) Stranding Records.

Laake JL, Lowry MS, DeLong RL, Melin SR, Carretta JV (2018) Populationgrowth and status of California sea lions.J Wildl Manage82: 583–595 .

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