Hundreds of dolphins and four whales have washed ashore along the coast of California since March, puzzling scientists. What's causing the phenomenon? Who is responsible for these marine creatures ending up dead on the beaches? Experts collected the carcasses and decided to study them to reach the root cause.

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They found that something had poisoned the whales and dolphins. A team from the National Oceanic and Atmospheric Administration studied the 50 dead dolphins and four whales and concluded that they died from neurotoxins produced by a harmful algal bloom.

These toxins attack the nervous system and can even cause death. NOAA further said that several more of these marine animals had lost their lives. “Hundreds of additional dolphins and sea lions have also died in other areas of California since the first domoic acid impacts were detected near Los Angeles in February,” NOAA said in an update.

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Most of the dolphins that had died were adult male long-beaked common dolphins. A few others were short-beaked common dolphins, while two were pregnant females.

Neurotoxin poisoned the dolphins

NOAA said that 14 of the dolphins had been tested so far, and 11 of them were found to have high levels of domoic acid. “One showed both domoic acid and saxitoxin, a different neurotoxin produced by another marine microorganism that causes paralytic shellfish poisoning."

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Scientists say that the ongoing harmful algal bloom has proved to be a death sentence for several creatures living along the coast of California. A type of algae called Pseudo-nitzschia australis releases Domoic acid, which gets collected in fish. When marine mammals eat them, it is passed on to them. The neurotoxin then attacks the brain and heart, causing seizures and permanent brain damage. 

NOAA says that in March, they had more than 100 calls about dead sea lions and dolphins washing up on the beaches. This is the fourth consecutive year when such a bloom has been reported.

Oceans have been warming because of climate change, triggering the growth of these algae.