Compared to just over a century ago, the pH-value of the sea’s surface water has gone down by 0.1 (i.e. 25 percent). This has caught the attention of Jon Havenhand and Michael Thorndyke, researchers at the University of Gothenburg, and they have together with colleagues in Australia studied if and how this decrease affects marine animals.

spatangus purpuerus – Sea urchin

As part of the study, Havenhand and Thorndyke used sea urchins of the species Heliocidaris erythrogramma to study reproduction. Sea urchins reproduce by releasing eggs that are fertilized out in the open water. In the study, Havenhand and Thorndyke studied breeding sea urchins in water where the pH-value had been lowered from its normal 8.1 down to 7.7. This might not sound as a significant drop, but a change from 8.1 to 7.7 means that the water becomes three times as acidic as before.

Havenhand and Thorndyke found out that in this changed environment, the sea urchins’ ability to reproduce was decreased by 25 percent. The low pH-value made the sperm swim slower than normally and move less effectively, which lowered the fertilization rate. But the problems didn’t stop here; when an egg was fertilized, the low pH-value could interfere with larval development and this too decreased the amount of eggs that actually developed into healthy sea urchin larvae.

More research is now needed to find out if these reproductive problems linked to acidification can be observed in other marine animals as well.