A new research, published Wednesday in the journal Science, concludes that the biggest marine animals are more likely to get extinct than the smaller ones. The researchers studied fossils belonging to ancient marine animals, some as old as 445 million years old, and found out that past mass extinctions have affected animals of all sizes equally. However, this recent “sixth mass extinction,” that many scientists say the world is currently facing has an unsettling pattern, in which all the top predators from the seas will disappear.
Jonathan Payne, the first author of the study and a paleobiologist at Stanford University, says the Earth is facing an “uncharted territory” that has never been “experience before” in a natural way.
“We might be skimming off the top of the food web, or changing the distribution of temperature and energy. A blue whale diving down to feed might mix a whole lot of ocean water. A larger clam will mix more sediments than a smaller one,” said Heim, a postdoctoral researcher in Payne’s lab who agrees with him.
A professor of conservation ecology at Duke University, weigh Pimm, also gave declarations to the Washington Post, even though he was not part of the study. For him, the extinction of the biggest animals of the ocean could completely change the “way oceans works” and its “marine ecology.”
The researchers analyzed the data available to almost 2,500 marine animals, vertebrates, and mollusks, in danger of extinction or already gone. For the endangered animals they used the International Union for Conservation of Nature’s Red List of Threatened Species data, and for the extinct animals, their fossils.
The team focused on four particular elements, whether the animal was a predator or not, if it lived in the seafloor or open water if it moves around or simply lays on the ocean floor, and finally, its size.
Afterward, they thoroughly analyzed if these four elements were correlated with the different mass extinctions since the Earth’s creation. They also studied the “background extinction rates,” which according to Heim are comprised of the “regular” extinction dictated by nature, in which the less adaptable species go extinct and are quickly replaced.
During the past five mass extinctions, those animals that were smaller were more likely to perish, just like moving animals, and those who lived in open waters. Nonetheless, this pattern has changed in the last half thousand years.
Now, size is the biggest cause of extinction, with the largest animals dying off first. The study concluded that those animals that are bigger have a factor of thirteen for every decennial: simply put, a big creature, ten times larger than one smaller, have thirteen times more probabilities of going extinct.
A manmade extinction
As stated by Payne, the scientists were caught by surprise by the study results. Nonetheless, after analyzing the historical context, they were not that shocked: it had to be human civilization, more specifically human hunting.
According to Heim, it is easier for human to hunt biggest animals since it takes less energy and can feed more individuals. For example, it is more efficient to kill a single blue whale that the equivalent ten tons of fish.
Fortunately, nature is very resilient, and if left alone, to live, animals’ populations tend to recover. For example, both Heim and Payne mentioned the elephant seal, which had gone practically extinct in the early 20th Century, but whose population has stabilized after law protection.
“There were somewhere around 100 left at the turn of the 20th century, but now there are 200,000 individuals. We have the capacity to degrade the system, but there are hopeful examples that suggest if we change what we are doing, we can have a positive impact” said Heim.
The other authors agree, stating that populations of blue and gray whales, that were almost extinct have also bounced back, so there is still time for humans to change.
Mass extinctions and famous specimens
Of all five past mass extinction, the Pernian one was one of the biggest, which occurred about 252 million years ago. This is why it was The nicknamed The Great Dying. Only four percent of the life on Earth survived, and all species that are alive today came from that tiny surviving amount.
However, the most famous one has to be the Cretaceous-Tertiary mass extinction that happened sixty-six million of years ago. It was during this event that dinosaurs disappeared, and so did three-quarters of the living creatures on Earth.
In the last five hundred years, there have also been famous extinctions related to size. For example that of the Dodo, which was one meter tall and could weight almost twenty kilos. The flightless bird was first seen by westerners on 1598, thanks to Dutch sailors who arrived on the island of Mauritius. In a few years, it was relentlessly hunted, until it was last seen on 1662.
More recently is the case of the Tasmanian Tiger, which also became extinct in the thirties after also being horribly hunted by bounties. The Tasmanian Tiger was also the biggest marsupial, and it has survived on the island of Tasmania after it had already disappeared in New Guinea and Australia. It is believed that the last Tiger was hunted in the 1910s, and the last captive specimen died in Hobart Zoo in 1936.
Source: Los Angeles Times