An Ancient Whale Graveyard’s Culprit: Toxic Algae

In 2010, the fossilized skeletons of several large marine animals were discovered in Chile during a highway-expansion project. After studying the fossils, scientists discovered that the animals had actually been stranded over time, some 6-9 million years ago, during four distinct events. What caused the repeated mass strandings and deaths? The most likely culprit turned out to be toxic algae, or harmful algal blooms (HABs).

Not only were many whales found at the site – including more than 40 baleen whales, a certain species of sperm whale, and a walrus-like whale (the latter two are now extinct) – but a number of other types of large marine animals were there as well. For example, fossilized seals, billfishes (predatory fish with prominent bills, such as sailfish and marlin), and aquatic sloths (belonging to the extinct genus Thalassocnus) were also graveyard residents. By looking at how the remains were deposited, the researchers figured out that the animals had died at sea and then been washed to shore, where the fossils were found. And the cause of the four separate events – which likely took place within 10,000 to 16,000 years of each other – had always been the same: HABs.

How exactly did the HABs come about? Normally, water environments have tiny, single-celled, plant-like organisms living in them called microalgae (or phytoplankton), and they’re at the bottom of the food chain. Most microalgae are harmless, but about 2% are known to potentially be toxic. For example, one of the most infamous is Karenia brevis, a dinoflagellate that makes brevetoxin, which is a neurotoxin that can contaminate shellfish and cause neurotoxin shellfish poisoning in anybody who eats the contaminated shellfish. Other types of microalgae make different toxins. Certain conditions – such as increased amounts of nitrogen in the water from farm fertilizer runoff – can cause these harmful microalgae to flourish, leading to a HAB. (Blooms of the red and brown K. brevis are notoriously known as “red tides.”) In the case of this ancient whale graveyard, scientists think that iron running off from the iron-rich Chilean coast likely triggered the periodic HAB events.

You can take 3-D tours and see videos and pictures of the fossil graveyard discovered in Chile at the Smithsonian’s Cerro Ballena webpage.

This ancient whale graveyard is just another reminder of how changes in microscopic life can have huge effects, and why it’s so important to not overlook how we affect them.

For further reading:

• Nicholas D. Pyenson et al.’s article “Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea“
• ScienceDaily’s article “Mass strandings of marine mammals blamed on toxic algae: Clues unearthed in ancient whale graveyard”
• Smithsonian’s Cerro Ballena webpage
• Center for Disease Control and Prevention’s webpage Harmful Algal Blooms (HABs)
• Teisha J. Rowland’s book Biology Bytes: Digestible Essays on Animals Both Commonplace and Bizarre