standard Tipping point for coral reefs?

Climate change has a tremendous impact on fauna living in coral reefs along with the corals themselves. Animals that live in the corals are moving to more suitable water temperatures as their habitats are heating up, while also being impacted by the increased presence of carbon dioxide in the oceans. This has resulted in a 30 percent increase in acidity over the past 250 years according to researchers with the Alfred Wegener Institute, the University of Gothenburg and the Rosensteil School of Marine and Atmospheric Science who announced their results at the AGU 2011 Meeting. Like animals and plants that live on land, sea fauna have a limited temperature range to live in. Ocean acidification enhances this sensitivity to their environment, especially when accompanied by thermal stress. The Earth’s oceans are a giant carbon sink.  As they continue to absorb more and more CO2 mostly produced from human industrial activities it lowers the Ph of the water shrinking the biogeographical range of fauna. Right now many ocean fauna are moving from place to place in order to escape areas with high acidification and increasing temperatures.

One of the problems with measuring the impacts of ocean acidification on different animal species in the ocean is that you can’t extrapolate from one species to another, but is possible to find unifying principles between different fauna, according to Dr Sam Dupont of the University of Gothenburg in Sweden.  What Dupont and other researchers have found is that ocean fauna are in need of more energy to survive so they can develop properly.  Ocean acidification slows this process or prevents it from happening altogether resulting in the death of species.  Lab studies reveal that when you decrease the level of Ph in the water some animals struggle, but there is a limit to what species can cope with if it continues to decrease.

Dupont’s research team looked at two different kinds of coral: the Mountain Star Coral and the Staghorn Coral. When exposed to 800 ppm of CO2 it stunted the growth of both species, but elevated CO2 did not cause bleaching — an effect that often occurs when the water temperature rises.  However, exposing the corals to +2° C and 800 ppm CO2 caused a decrease in growth rates for both species — 20 percent for the Mountain Star and 35 percent for the Staghorn.  Corals are highly sensitive to temperature.  Not surprisingly, when the corals were exposed to water temperature of 32° C, their growth halted completely. Interestingly, some animals that live in corals show tolerance to heat, such as the Clade D Symbiodinium.  So what is the overall ecological role of corals? Why should people care?  Dupont provided an urban analogy: Imagine if all the construction workers in San Francisco were to die due to elevated levels of CO2 in the atmosphere, there would clearly be potentially catastrophic knock-on effects to the rest of the city.  If all corals die off, the world’s oceans would be devastated.

Currently researchers are looking to move beyond lab studies in order to observe the ecological effects of rising CO2 levels and ocean acidification firsthand.  The plan is to bring lab and field data together in order to understand the role of temperature and its combined effects on the growth of corals.  More research is needed on the combined effects of CO2 and increased Ph on larvae, which results in slower growth, but some fauna have developed a physiological tolerance to CO2.  Researchers also need to be aware of where organisms are located in reference to their normal temperature thresholds, as well as unique cases where a rise in temperature could also be beneficial.

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