A study published in an upcoming issue of the journal Current Biology paints a grim picture of the future impact of ocean acidification on marine organisms, reports ENN's Angelique van Engelen. While the study doesn't contribute much that is new in terms of our current understanding of the process -- indeed, the scientists' estimation that seawater pH will drop to 7.7 from a normal 8.1 is well in line with most estimates -- it provides yet more evidence that acidification will devastate many forms of marine life in the near future.
http://www.nas.nasa.gov/About/Education/Ozone/ozonelayer.html
Tripling of seawater acidity expected by 2100
Jon Havenhand and Michael Thorndyke of the University of Gothenburg subjected sea urchins to an environment whose seawater pH had artificially been reduced from 8.1 to 7.7; in other words, its acidity was tripled. They found that the increased acidity significantly lowered the urchins' ability to reproduce -- up to 25% -- by inhibiting the movement of their sperm. For those cases in which fertilization was successful, only 75% of the resultant eggs developed into larvae.
A 25 percent drop in fertility is the equivalent of a 25 percent drop in the reproductive population. It remains to be seen whether other species exhibit the same effect, but, translated to commercially and ecologically important species such as lobsters, crabs, mussels and fish, acidification would have far reaching consequences, said Havenhand.
Assessing the impact of ocean acidification on marine life
Like other marine organisms whose shells or skeletons are made of calcium carbonate (i.e. limestone), sea urchins suffer when the pH drops. The lower pH inhibits these organisms' growth by dissolving their shells and, in more extreme cases, prevents it altogether (see: corals). I wrote about a similar study a few months ago (on World Ocean Day, appropriately enough) which examined the impact of low pH water -- down to 7.4, in some places -- on a variety of organisms, including corals, calcifying algae and sea snails. Not surprisingly, the results were equally discouraging:
"The results were stark: No corals were present, mollusks were seen with their shells dissolving (none were present in area with a pH of 7.4) and calcifying algae (those that form calcium carbonate skeletons) were often displaced by non-calcifying species like seagrasses, which benefited from the extra carbon dioxide. Overall, the number of species present near the vents was 30 percent lower when compared to neighboring areas."
While some may benefit over the short-term, including several species of phytoplankton, the long-term impacts of ocean acidification are unequivocally bad.
http://www.treehugger.com/files/2008/06/future-ocean-acidification.php
http://www.treehugger.com/files/2008/07/noaa-report-corals.php
http://www.treehugger.com/files/2007/11/shellfish_ocean_acidification.php
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