RSS Acidic oceans, not warmer oceans are making it harder for baby corals to survive

MASA Admin

8 May 2007
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We’ve all heard the story, the worlds oceans are become more acidic which is bad news for corals. A new study published Friday in the journal Science Advances suggests that ocean acidification may be affecting the growth rates of baby corals by causing deformities in their skeletons.

Using a high-resolution 3-D x-ray microscope and scanning electron microscope researchers found that more acidic water (those that have absorbed more atmospheric carbon dioxide) can cause structural deformities in the skeletons of juvenile corals. The juvenile skeletons were more prone to missing sections and more likely to have fragile porous surfaces.

The skeletons of newly settled coral recruits of Acropora spicifera were grown for 1 month under four different combinations of temperature and pH. The corals which were growing in water at 24oC and 7.7pH had the least developed and most porous skeletons at the end of the study.

X-ray microscopy and SEM images of 1-month-old coral skeletons under the four temperature-PCO2 treatments (A to P). [Science Advances]

Any pH reading below 7 is considered acidic while the average pH reading for seawater should be between 7.5-8.5. After seeing these results (corals grown in 7. 7pH) we wonder how far pH can drop before corals can no longer settle out. While many are focusing on el nino and warmer ocean temperatures which cause wide spread coral bleaching, ocean acidification may turn of to be the bigger threat to reefs.

Although other studies have shown the effect of ocean acidification on coral growth rates, researches also discovered that growing corals in higher temperature didn’t have any negative effect on the growth rates of coral. This was previously undocumented and in fact, warmer temperatures seemed to lessen the effects of carbon dioxide.

Dr. Taryn Foster, the study’s lead researches offered a possible reason for the mitigating effect of higher temperatures: “Juvenile corals move a lot, sometimes hundreds of kilometers, so they might need to withstand a range of temperatures in their life cycle.” The study was conducted in the subtropical Indian Oceans of the Abrolhos Island off the west coast of Australia where water are typically cooler than equatorial regions.

But even if warmer temperatures aren’t a problem for coral in the subtropics, the effects of ocean acidification are still worrisome, Dr. Foster said, because young coral help reefs maintain genetic diversity and recover after damaging events.

However, she was cautious about the implications for global reef development: “This is only one species of coral, and we think this is unique to the subtropics.” This study drives home the point to keep up a high pH in your home aquarium for optimum coral growth and health. [NY Times]

Fractures and deformed skeletal structures in high PCO2–treated corals. [Science Advances]

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