Some experts fear that the Earth is more likely to be pushed past its tipping point by numerous small climate-change perturbations rather than a single massive upheaval.
Consider the plight of the lowly ocean periwinkle, a.k.a. Littorina littorea, once a staple of street stalls in cockney London. That delicious catchphrase “to winkle something out” derived from using a wire hook to extract this snail from its shell.
“To winkle” might soon come to mean “to warn about indirect ecosystems shifts from climate change.” That’s a definition suggested by some elegant research from the University of Plymouth published in the current issue of Biology Letters from the Royal Society in Britain.
Research has already shown that excess atmospheric carbon dioxide from human activity is shifting the oceans from being base (like ammonia) to acid (like vinegar). That increased acidity disrupts the ability of ocean critters to make skeletons and shells through a process called calcification.
Marine biologist Ruth Bibby and her Plymouth colleagues asked about the impact of acidification on periwinkle survival. Periwinkles are one of several species that thickens its shell after sniffing a trace of crabs or other crushing predators.
The Plymouth research found that this defensive response doesn’t kick in when the water is even mildly acidic. The pH of the acidic water in the their experiment was 6.45 (7 is neutral). The pH of most seawater is just below 8 but dropping fast.
Living for 15 days inside protective plastic pots in the same aquarium as carnivorous crabs, periwinkles bulked up shell thickness at their most vulnerable spot by as much as a third when in normal sea water. But they added nothing in the acidified water.
Later, the thinner shelled periwinkles were three times more likely to crawl to the water surface when crab scent was present.
If periwinkles are increasingly falling victim to crabs or expending energy by running away, their numbers will drop. Since they are a vital part in the food chain in the shallow waters between the high and low tide levels, this decline could have what the researchers call “major ramifications.”
thestar.com, 28 October 2007. Article.
