Toxic Algae Most Likely Cause Of Ancient Chilean Whale Strandings
February 26, 2014

Toxic Algae Most Likely Cause Of Ancient Chilean Whale Strandings

Brett Smith for - Your Universe Online

A site in the Atacama Desert of Northern Chile has become well known for its wealth of ancient marine mammal fossils, deposited there by a series of mass strandings.

While the cause of whale or other mammal strandings that take place today can often be identified, the cause behind ancient strandings is much more difficult to pin down.

According to a newly published report in the Proceedings of the Royal Society B, an international team of scientists has been able to determine the culprit behind the repeated mass strandings at the Chilean site known as Cerro Ballena: toxic algae.

Modern-day toxic algae, such as the "red tides" seen along the Gulf Coast, are a common cause of repetitive mass strandings of large marine animals. These deadly algae are fueled by iron and other nutrients that are released by erosion and carried to the sea by rivers.

"There are a few compelling modern examples that provide excellent analogs for the patterns we observed at Cerro Ballena—in particular, one case from the late 1980s when more than a dozen humpback whales washed ashore near Cape Cod, with no signs of trauma, but sickened by mackerel loaded with toxins from red tides," said study author Nicholas Pyenson, a paleontologist at the Smithsonian's National Museum of Natural History.

"Harmful algal blooms in the modern world can strike a variety of marine mammals and large predatory fish,” Pyenson added. “The key for us was its repetitive nature at Cerro Ballena: no other plausible explanation in the modern world would be recurring, except for toxic algae, which can recur if the conditions are right."

For the study, a team of Smithsonian 3-D imaging specialists traveled to Chile and scanned the full dig site. Although all of the fossils located from 2010 to 2013 have been transferred to museums within the Chilean towns of Caldera and Santiago, the Smithsonian was able to store the digital information, including 3-D scans.

The scientists found that toxins generated by algal blooms probably poisoned many marine vertebrates near Cerro Ballena between 5 and 11 million years ago. The toxins may have been ingested via contaminated prey or through inhalation, causing a relatively speedy death at sea.

The bodies of these animals then floated towards the coastline and were washed in to a tidal flat by the surf. Once stuck on the flat, the bodies of these creatures were protected against marine scavengers -- as there were no large land scavengers in South America at this time. Gradually, the bodies were entombed by sand.

Because there are four distinct layers at Cerro Ballena, this pathway from sea to land occurred four different times over 10,000 to 16,000 years, the study team said.

"Cerro Ballena is the densest site for individual fossil whales and other extinct marine mammals in entire world, putting it on par with the La Brea Tar Pits or Dinosaur National Monument in the U.S.," Pyenson said. "The site preserves marine predators that are familiar to modern eyes, like large whales and seals. However, it also preserves extinct and bizarre marine mammals, including walrus-like whales and aquatic sloths. In this way, the site is an amazing and rare snapshot of ancient marine ecosystems along the coast of South America."