Ocean acidification tips predator-prey balance

The lowly sea snail, a slow-moving denizen of tide pools up and down the California coast, could be in big trouble as greenhouse gases change the world’s climate and increase the acidity of the oceans.

The snails are the favorite prey of the voracious purple sea stars. In any natural tide pool, they will quickly flee from their predator to a nearby dry rock, because the starfish rarely leave the water.

Now a young biologist at the Bodega Marine Laboratory in Bodega Bay has discovered that the increasing pace of ocean acidification can deeply alter the relationship between prey and predator — to the sea snail’s disadvantage. Her experiments may well foreshadow major changes in the life of the open oceans everywhere.

For the past four years, Brittany Jellison, 27, has been studying the relationship between the black turban sea snail and the purple sea star, its dominant predator, as they thrive in the rocky tide pools of Bodega Bay.

Escape routes charted

In the lab, she has used chemical traces of the starfish bodies to observe the snails’ reactions and chart their escape routes as they flee from the starfish they perceive is looming. Jellison has measured the snails’ pathways and their speeds as they crawl up the slopes of their tanks.

“Those snails can move faster than you’d think when they feel they’re at risk of being eaten,” Jellison said.

As fossil fuels continue burning, carbon dioxide, their major greenhouse gas, saturates the water of the ocean and increases its corrosive acidity year by year, climate scientists continually warn.

And a growing body of research is finding, many animals in the ocean, with or without shells, are showing the effects of those increases in acidity. Oysters and mussels are building thinner shells; predatory fish can become reluctant to attack traditional prey; and some prey seem only too eager to be eaten. Some fish can lose their sense of smell or hearing, and some fish larvae can be attracted to the very predators and habitats they would naturally flee or avoid.

In the Bodega lab, Jellison set out to determine just how ocean acidity can affect the relationship between the snail and its predator. She devised a meticulous series of experiments, some involving 32 snails living in water of varying acidity, and exposed to chemical traces or “cues” from the bodies of five sea stars. She conducts her experiments in 10-gallon plastic tanks that duplicate the typical density of Bodega Bay’s rocky tide pools.

Her work is among the first to show how step-by-step increases in ocean acidity can affect the lives of animals now and in the future, her senior adviser said.

Impact of rising acid

During one phase of her experiments, Jellison varied the water’s acidity 16 time in a series that ranged from the average acidity of the world’s oceans today to the higher levels that virtually all climate scientists agree are likely by the end of this century as global warming continues.

Every two minutes for 28 minutes, Jellison and colleagues photographed each snail in its simulated tide pool as it sensed the chemical cues from its enemy and recorded each snail’s movements as it left the water. They repeated this for each of the snails at all of the water’s 16 acidity levels.

Analysis of the photographs showed these clear results: As the water grew more acidic, the flight responses of the snails and the paths they took as they fled became more and more disrupted, Jellison said.

“Behavioral impairments that (Jellison) documented may become more common and more extreme in coming years, and may foreshadow other shifts in the ecosystem” said Brian Gaylord, professor of evolution and ecology at UC Davis and a senior researcher at the Bodega lab. “It could signal shifts to many links within the overall food web.”

The details of Jellison’s research are being published in Proceedings B of the Royal Society. Her colleagues include Gaylord, Aaron T. Ninokawa, Tessa M. Hill and Eric Sanford.

David Perlman, San Francisco Chronicle, 4 July 2016. Article.

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