Purple Urchins Quickly Adapt To Acidic Oceans
June 13, 2013

Purple Urchins Can Quickly Adapt To Acidic Oceans

Brett Smith for redOrbit.com - Your Universe Online

As the levels of atmospheric carbon dioxide increase, the oceans are projected to absorb more of the greenhouse gas, leading to acidification of the water. This shift in oceanic chemistry is expected to negatively impact countless species. However, a new study from the University of California, Santa Barbara has found that purple sea urchins Strongylocentrotus purpuratus are capable of evolving in a way that copes with potential negative impacts of ocean acidification.

"What we want to know is, given that this is a process that happens over time, can marine animals adapt? Could evolution come to the rescue?" explained study co-author Morgan Kelly of UC Santa Barbara's Department of Ecology, Evolution and Marine Biology.

Ocean acidification is expected hinder urchins and other calcifying creatures´ ability to create and maintain their hard shells and exoskeletons.“¯The increased acidity causes a drop in the levels of calcium carbonate, resulting in smaller animals, thinner shells and an increased risk for shorter urchin spines.

"It gives them osteoporosis," Kelly explained.

According to the study, which was published in the journal“¯Global Change Biology, the UC Santa Barbara researchers began by collecting specimens at two locations off the California coast — a northern site and a southern site. The two groups were interbred and the spawned larvae were raised in the acidic conditions projected for future oceans.

"We exposed them to 1,100 parts per million of carbon dioxide," Kelly said.

Highest detected levels of oceanic carbon dioxide are about 400 parts per million and are expected to increase to an average of 700 parts per million by the end of the century.

Under these ℠futuristic´ conditions, the urchins tended to develop into smaller-than-average sizes, but the researchers noted a wide variation in size. This finding indicated that some of the larger urchins had inherited a tolerance for higher carbon dioxide“¯levels, Kelly said.

The more tolerant urchins are then expected to spawn more offspring than their smaller, more vulnerable counterparts, causing a rapid evolution of the purple urchin.

"This is what allows us to predict that this species will evolve increased tolerance — as CO2“¯rises, urchins that have greater tolerance will have a better chance of survival, and they will pass on their greater tolerance to their offspring," Kelly said.

The findings are good news for the urchins, their predators and those concerned about the effects of ocean acidification. The study also emphasizes that future studies need to take into account adaptive measures when determining how a species will respond to climate change.

"We don't expect evolution to completely erase the effects of ocean acidification, but we do expect evolution to mitigate these effects. And the more heritable variation there is, the greater the power of evolution to mitigate the effects of climate change," said Kelly.

Purple sea urchins are considered to be a keystone species because their presence plays a vital role in the undersea ecosystem. If they were to die off in significant numbers — seabirds, fish and other predators would lose a significant food source.

The researchers say they are conducting similar acidification“¯studies on other marine species, including red urchin, coral, algae and the California mussel.