Carbon levels in our air are reaching unprecedented levels, and the climate is warming. It’s estimated that a quarter or more of the carbon entering our atmosphere from burning fossil fuels is absorbed by the world’s oceans. All that carbon is overwhelming the buffering system that stabilizes the pH of the sea and is acidifying the oceans. Researchers are trying to learn more about how marine animals will deal with both rising temperatures and a more acidic ocean. New work has indicated that most species require large numbers to sustain their population effectively; survival may become difficult for many.
This study has investigated the response of a huge number of sea urchin larvae to moderately or extremely acidic seawater. These findings have been reported in the Proceedings of the Royal Society B. Research leader and University of Vermont biologist Melissa Pespeni said that for many species, "we'll need large populations.”
Pepsini’s team identified a rare change in the genomes of a few of the sea urchins that was especially helpful for their survival. Only a small minority carried the genetic variants, which are "a bit like having one winter coat among fifty lightweight jackets when the weather hits twenty below in Vermont," Pespeni explained. "It's that coat that lets you survive."
In the extremely acidic conditions, the rare variants became more common in the larvae. These variations enable changes in protein function in the urchins so they could deal with the acidity. Importantly, however, a very large population size is necessary to maintain the variants in the urchin genome. This work utilized 25 adult urchins from the wild, and the females generated about 20,000 viable larvae after producing around 200,000 eggs.
"The bigger the population, the more rare variation you'll have," said the lead study author Reid Brennan, a post-doctoral researcher in the Pespeni lab. "If we reduce population sizes, then we're going to have less fodder for evolution and less chance to have the rare genetic variation that might be beneficial."
Surely, some organisms will survive in a world with a changing climate; they will be able to migrate to a better area or tolerate the shifts. But other species will have to evolve or perish.
"This species of sea urchin is going to be okay in the short term. They can respond to these low pH conditions and have the needed genetic variation to evolve," said Brennan. "So long as we do our part to protect their habitats and keep their populations large."
"It's hopeful that evolution happens, and it's surprising and exciting that these rare variants play such a powerful role," added Pespeni. "This discovery has important implications for long-term species persistence. These rare variants are a kind of currency that urchins have to spend. But they can only spend it once."