Description

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Context

A harmful algal bloom off the California coast has led to the release of a neurotoxin called domoic acid which is causing neurological disorders and aggression in sea lions resulting in attacks on surfers and beachgoers.

About Sea Lions

Feature	Description
Taxonomic Family	Otariidae (eared seals), includes 5 species
Habitat	Coastal waters of the North and South Pacific Ocean particularly western coasts of North America, from southeast Alaska to central Mexico
Physical Characteristics	External ear flaps, long front flippers, mane-like fur in males, can weigh up to 545 kg
Behaviour	Social, often seen in groups on rocky shores or floating in the water in rafts; generally non-aggressive
Lifespan	20–30 years in the wild
Diet	Carnivorous; feeds on squid, anchovies, sardines and mackerel

What Is Causing the Aggression?

Cause	Explanation
Toxin Involved	Domoic acid
Algae Source	Produced by the diatom algae Pseudo-nitzschia which thrives in nutrient-rich waters during algal blooms
How it Spreads	Toxin bioaccumulates in small marine organisms → consumed by larger fish → eaten by sea lions
Effect on Sea Lions	Neurological symptoms: seizures, disorientation, lethargy, abnormal aggression
Human Risk	Though rare, domoic acid poisoning (amnesic shellfish poisoning) can also affect humans, especially via contaminated shellfish

About Domoic Acid

Naturally occurring neurotoxin.

Binds to glutamate receptors in the brain leading to excitotoxicity and neuronal death.

Symptoms in Sea Lions are Head weaving, muscle tremors, aggressive behaviour, lethargy.

Symptoms in Human include Nausea, vomiting, memory loss, seizures (in severe cases).

Concerns

Aspect	Detail
Algal Bloom Drivers	Eutrophication due to agricultural runoff, climate change (warming seas), altered nutrient cycles
Harmful Algal Blooms (HABs)	Disrupt marine food chains, reduce biodiversity, affect fisheries and aquaculture
Bioindicator Species	Sea lions serve as bioindicators for marine pollution and ecosystem health
Climate Link	Rising sea temperatures and upwelling intensify HABs making such events more frequent and dangerous