Environment

Rising ocean acid levels skew predator/prey relationship

Normally, black turban snails (top) escape predation by sea stars by crawling out of tide pools
Normally, black turban snails (top) escape predation by sea stars by crawling out of tide pools
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Normally, black turban snails (top) escape predation by sea stars by crawling out of tide pools
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Normally, black turban snails (top) escape predation by sea stars by crawling out of tide pools

The rising tide (no pun intended) of acid in the Earth's oceans could cause a major disruption in the delicate balance of its ecosystem. A new study suggests that changes in the ocean's acidic levels due to atmospheric carbon dioxide could also change the predator-prey relationship of ocean life by tipping the scales in favor of the predator.

The study was conducted by the University of California, Davis at the UC Davis Bodega Marine Laboratory. It examined the behaviour of ocre sea stars (predators) and black turban snails (the sea stars' prey), two common species taken from tide pools at the Marine Reserve, in seawater with varied pH levels. Researchers simulated "16 discrete levels of pH" starting from present acidity levels to the levels they are expected to reach by 2100, according to the study's abstract.

The snails started to show signs of a weakened defense when the pH level in the seawater fell to 7.1 and lower. Black turban snails ordinarily crawl out of the tide pool to avoid being eaten, since ochre sea stars rarely exit the water to capture their prey. The study says that the snails not only spent less time in such "refuge locations," but they also failed to recover their ability to escape from predators in waters with fluctuating acidity levels.

The study does not show why the rise of acid in seawater causes these snails to move slower when responding to a predator, or if the snails could learn to adapt to their surroundings.

An observation based study of the Atlantic Ocean's basin published last year in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS) found large decreases in pH levels in the South Atlantic Central and North Atlantic Central waters that "trended towards zero in deep and bottoms waters."

Brian Gaylord, a professor of evolution and ecology at the Bodega Marine Laboratory, says that these tide pool experiments could lead to the discovery of future disruptions in other ocean organisms' predator-prey relationships due to rising acidity levels.

"Dozens of West Coast species display escape responses to sea stars," Gaylord says. "We don't yet know the extent to which ocean acidification could alter these additional predator-prey interactions, but there is clear potential for broader disruption of links within shoreline food webs."

Ocean acidification has lead to mass extinctions of oceanic life in the past. A study conducted by the University of Edinburgh found that more than 90 percent of marine life and two-thirds of land animals died off more than 252 million years ago due to a rise in ocean acidity levels over a 60,000 year period. Data taken from rock samples collected in the United Arab Emirates region of the Middle East showed that eruptions from the large volcanic rock region known as the Siberian Traps poured carbon dioxide into the atmosphere and led to ocean acidification that lasted around 10,000 years.

The study was published in the journal Proceedings of the Royal Society B.

Source: UC Davis

5 comments
aksdad
"The study does not show...if the snails could learn to adapt to their surroundings." Excellent point. All laboratory studies of organisms in artificially low pH seawater introduce their subjects to a rapid change in their environment that doesn't reflect the very slow process that may occur in the oceans. It's a poor experiment that doesn't account for the adaptability of organisms, especially over multiple generations. It essentially tells us nothing useful except these organisms don't handle a major change in pH over days or weeks. On the other hand, ocean pH studies show that daily and seasonal fluctuations in seawater pH--greater than the relatively slow long term change--are common and it doesn't seem to bother most marine life. Interestingly, though physics tells us that ocean pH should decrease as atmospheric CO₂ increases, according to measurements it isn't happening except in a few places. You can see for yourself here: http://www.pmel.noaa.gov/co2/story/OA+Observations+and+Data Only a very few sites show decreasing pH, for example, here: https://www3.epa.gov/climatechange/science/indicators/oceans/acidity.html I haven't read any explanations for the discrepancies, but what is being said about ocean acidification and what's actually being measured are quite different.
Anne Ominous
Highly speculative to the point of alarmism. As another comment has already stated, we aren't actually seeing decreases in ph above noise levels except in a very few places, and we are actually seeing increases in a few places too. The Ocean Acidification Alarmists have not been able to explain to us how corals and giant ammonites for example, with their massive carbonate superstructures, could ever have existed at the time they actually evolved, during periods with many times the atmospheric CO2 we have today.
Nik
Atmospheric CO2 levels are a political red herring, and can be safely ignored.
PeterOsborne
As water warms, it holds less CO, and becomes more alkaline not more acid. Deep water acidity might be due to deep water volcanic eruptions.
spicedreams
'large decreases in pH levels in the South Atlantic Central and North Atlantic Central waters that "trended towards zero in deep and bottoms waters." ' What that literally means, and the cited study confirms it, is that there was almost zero change in pH in deep waters. @aksdad, you say 'according to measurements' ph decrease 'isn't happening except in a few places'. Yet both the sites you link to show significant decreases in pH at each location, and no locations where it is not decreasing.