With warming sea temperatures and increased algal blooms due to eutrophication, disoriented and neurologically impaired sea lions have appeared across different coasts. A special neurotoxin found primarily in crustaceans called domoic acid can lead to amnesic shellfish poisoning within mammals, which can be fatal. Domoic acid is sourced from algae located within the water column that tend to be preyed on by crustaceans. The food chain furthers the transfer of domoic acid between different trophic levels, which leads to the destruction of the neurological systems of most mammals.
Why Does This Happen?
Algal blooms typically occur within an area concentrated in nutrients and compounds that enrich and support their rapid growth. The alarming increase in the prevalence of climate change and the toll it has taken on the oceans has supported algal blooms through the rise in ocean temperatures, and due to eutrophication caused by agricultural development. However, while these rising conditions are better for the algae, it has brought on increased fatalities within the rest of the marine ecosystems.
Domoic acid poisoning has become more common in marine mammals simply because of this. Mammals, like sea lions, take in the neurotoxin by eating fish or other prey that acquire the toxin within crustaceans. The toxin begins to deteriorate and attack certain neurological processes that leads to disorientation and possible convulsions within sea lions. The Marine Mammal Center states that over 20 sea lions had turned up sick this past year on the California coast with symptoms of lethargy and the inability to move. With the precautions needed to be taken due to the ongoing pandemic, taking care of impaired sea lions has become increasingly difficult and sometimes impossible to do.
Not only is the presence of this neurotoxin already damaging for the sea lion affected, but these health implications can be passed onto their pups, which causes brain defects upon birth. Sometimes, the vitality of the fetus is put in danger as it can come out stillborn, miscarried, or even potentially aborted from their mother. The chances of survival sometimes becomes so minimal that brain damage is inevitable if the pup is birthed.
How Can This be Treated?
While treatment is not readily available for domoic acid poisoning nor has it been completely developed, scientists are constantly looking into potential treatments for marine animals. Cellular therapy done by the University of California, San Francisco (UCSF) treats epilepsy in sea lions caused by the ingestions of such algal toxins has shown promising results. Medial ganglionic eminence (MGE) cells extracted from pig embryos and transplanted into the hippocampi of sea lions help to surgically repair the neural networks within the brain that cause seizures. At the moment, the discovery of this treatment has not been widespread as UCSF researchers struggle to increase their horizon due to COVID-19 restrictions and other problems brought on by the pandemic. Research poses harm to both the scientific community and the animals as most research is conducted by euthanizing a neurologically impaired sea lion for comprehensive research by their autopsies.
On a much broader scale, efforts towards the mitigation of climate change need to prevail. There needs to be more human efforts like decreasing plastic waste, extensive agricultural activity and deforestation, that all lead to increased algal blooms and contributes to the intensification of this growing global issue.
Loxton, M. (2020, June 23). An annual sea lion sickness is linked to climate change. 90.3 KAZU. Retrieved from https://www.kazu.org/post/annual-sea-lion-sickness-linked-climate-change#stream/0
Weiler, N. (2020, October 9). Struggling sea lions may benefit from UCSF neuroscience research. The Regents of The University of California. Retrieved from https://www.ucsf.edu/news/2020/10/418746/struggling-sea-lions-may-benefit-ucsf-neuroscience-research