Causes and Effects of Algal Blooms in the Bay
The following is a message from local scientist and PBCA member, Dr. Omar Clay, on pollution in Ensenada Bay and effects on local wildlife and seafood:
Have you walked the beach and noticed a sea lion struggling to move or an increase in the number of dead pelicans lately? If so, you are not alone. Punta Banda, along with most of coastal California is experiencing the downstream consequences of a process known as eutrophication. As a result of eutrophication, domoic acid poisoning is impacting our marine wildlife and if you are someone who consumes a lot of shellfish (e.g. mussels) it could impact you as well.
So, what is going on with domoic acid and how and why is impacting marine life? I’m getting these kind of questions a lot while in the process of monitoring mortality on the beach these days so I wanted to post about here for your consideration.
People who attended my presentation Co-piloting Spaceship Earth in the theater a couple of years ago may recall that I spoke about how humans are not just altering the natural carbon cycle but we are also impacting the nitrogen and phosphorus cycles. We influence both the nitrogen and carbon cycle through combustion reactions (like those in our vehicles) but the primary way we alter the nitrogen and phosphorus cycles is through agriculture. Nitrogen and phosphorus are essential macronutrients and key elements in DNA and proteins. Plant growth is often limited by the plant’s ability to access these two elements. As a result, it is common in agriculture to apply fertilizers that contain high concentrations of nitrogen and phosphorus. Unfortunately, in general terms, much (~67%) of the fertilizer applied to agricultural fields ends up running off into surrounding water-bodies. When agricultural runoff enters surrounding water bodies, they fertilize algae and can result in algal blooms. This is known as eutrophication or nutrient pollution. If you want to minimize your personal role in this process, consider consuming organic produce, as organic farms are required to limit the amount of fertilizer to their fields.
Algal blooms (aka red tides) have become a global problem for coastal ecosystems, as these areas receive a tremendous amount of agricultural runoff. We’ve seen a huge increase in the number and size of coastal algal (aka phytoplankton) blooms in recent decades. Locally, the influx of untreated sewage into the estuary is another rout by which nitrogen and phosphorus pollution is occurring. A sea-side golf course will also contribute to this problem. Blooms can be unsightly and after the algae dies off may result in the formation of a hypoxic (low oxygen) zone as the algal detritus is consumed by zooplankton which also use up the available oxygen. These dead zones can threaten marine life of all forms.
Some algal blooms are also a danger to other life forms because they generate toxins. Domoic acid is a neurotoxin that is formed by specific types of algal blooms. Domoic acid was first detected off the California shore in 1991 but has become increasingly common since then. Domoic acid is then taken up by shell fish (like mussels and krill) and subsequently enters the marine food web.
Seals, sea lions, dolphins, whales, squid and sea birds as well as some humans eat shellfish. Over time the domoic acid concentrations in the body can build up with continued consumption of shell fish. Locally sea lions and pelicans appear to be particularly susceptible to this process of bioaccumulation. Once the concentration of neurotoxin reaches a sufficiently high level it may lead seizures, aggressive behaviors, and partial paralysis. Sometimes you can see the fact that an animal is suffering from domoic acid poisoning because in side to side head weaving, extending their head backwards, foaming at the mouth, and or their eyes may become bloodshot and bulge outwards. Pelicans can actually fall from the sky during a seizure, which clearly can be fatal. Ultimately domoic acid poisoning can kill if untreated. If an organism suffering with domoic acid poisoning has a sub-lethal dose of domoic acid poisoning it may be able to recover by consuming food and water free of domoic acid contamination and essentially flush the poison from their system. Domoic acid is a neurotoxin and it may damage the brain, nervous system, and heart permanently.
In the last month we’ve seen a spike in dead sea lions, sea lion pups, and pelicans. Just today (4/4/25) there were three sea lions struggling to survive, two dead pups, and five dead pelicans. These are large numbers for this relatively small stretch of beach. Last month a dolphin with signs of domoic acid poisoning was also observed along with a sea lion and a pup.
If you encounter a sea lion struggling on the beach you should be sure not molest it and treat it with caution as it may be aggressive if it’s able to move. You may want to call PROFEPA (800-776-3372) or you can reach out to me via this email if you like. I also encourage people to spread the word that shellfish consumption is currently counter-indicated.
Paz,
Omar
Below are some images of sea lions in Punta Banda over the last 2 days, showing motions consistent with domoic acid poisoning:
Some references sources to support your critical analytic skills and follow up:
https://www.scientificamerican.com/article/algal-blooms-have-boomed-worldwide/
https://academic.oup.com/nsr/article/12/3/nwaf011/7951978
https://www.nature.com/articles/s41586-023-05760-y
https://www.marinemammalcenter.org/science-conservation/research-library/domoic-acid-toxicosis
https://marinemammalcare.org/conservation-and-research/domoic-acid/
