Wednesday, February 20, 2013

CO2 in oceans no threat to corals

Many marine organisms need CO2 to make their coral skeletons, carbonate shells and so on. Corals also have symbiotic plants within their flesh that use CO2 in photosynthesis.

Marine life flourishes where CO2 is abundant. Professor Walter Stark wrote about a favourite place for scuba divers, the ‘Bubble Bath’ near Dobu Island, Papua New Guinea. Here CO2 of volcanic origin is bubbling visibly through the water so that the water is saturated with CO2. Abundant life flourishes to make the spot a spectacular diver’s delight. He reported many accurate measurements of pH in the area and concluded “It seems that coral reefs are thriving at pH levels well below the most alarming projections for 2100.”

One of the factors affecting ocean pH is photosynthesis by plants. Experimental results show that plants grow better if CO2 is increased, and greenhouse managers commonly increase the CO2 artificially to increase crops, often by 30% or more. There is every reason to suppose that marine plants also thrive if CO2 is increased. There is also experimental evidence that carbonate secreting animals thrive in higher CO2. Herfort and colleagues concluded that the likely result of human emissions of CO2 would be an increase in oceanic CO2 that could stimulate photosynthesis and calcification in a wide variety of corals.

Marine life, including that part that fixes CO2 as the carbonate in limestones such as coral reefs, evolved on an Earth with CO2 levels many times higher than those of today, as reported by Berner and Kothaval. It may be true to say that today’s marine life is getting by in a CO2-deprived environment.

Tuvalu has long been ‘hot news’ as the favourite island to be doomed by sea level rise driven by global warming, allegedly caused in turn by anthropogenic carbon dioxide. But if a coral island is sinking slowly (or relative sea level rising slowly) the growth of coral can keep up with it. In the right circumstances some corals can grow over 2 cm in a year, but growth rate depends on many factors. Coral islands, made of living things, are not static dip-sticks against which sea level can be measured. We have to consider coral growth, erosion, transport and deposition of sediment and many other aspects of coral island evolution – not just the pH of seawater.


Wednesday, February 6, 2013

These corals would find global warming a snack

Hoagy and his friends screech about a 2 degree temperature rise killing off Australia's coral reefs.  In the Persian gulf, however an extra 8 degrees doesn't bother corals. And the Warmists below admit their confusion

We tend to associate coral reefs with tropical seas of around 28 degrees, where even slight warming can have devastating effects on corals. But in the Arabian/Persian Gulf, corals survive seawater temperatures of up to 36 degrees Celsius every summer, heat levels that would kill corals elsewhere.

In their study, the NOCS team worked closely with NYUAD researchers to select and characterise model corals from the Arabian/Persian Gulf, which will facilitate future molecular-scale investigations into why they can tolerate heat stress.

“We have established successful laboratory cultures of Gulf corals,” said Dr Jörg Wiedenmann, Head of the Coral Reef Laboratory and Senior Lecturer at University of Southampton Ocean and Earth Science, both of which are based at NOCS. “This will greatly accelerate the progress of unravelling the mechanisms that underlie their surprising heat resistance.”

Reefs are made up of many species of coral, each of which have a mutually beneficial, or “symbiotic”, relationship with algae living in their tissue. These algae supply vital nutrition to the host but are sensitive to environmental changes including increases in seawater temperature.

Even a temperature rise of just one degree Celsius can harm the symbiotic algae, which in turn can increase mortality in corals. The associated loss of symbiotic algae is known as “coral bleaching” because the white skeletons of the corals become visible through the tissue depleted from the algal pigments.

“In Gulf corals, both the coral host and the associated algal partners need to withstand the high seawater temperatures,” said Dr Wiedenmann who led the study.

But the scientists were surprised to discover that the algae in Gulf corals belong to a group not known for its thermal tolerance.

“We see that the algae are indeed special but in a way that we did not expect,” said Dr Wiedenmann. “The algae that we found in most of the corals in Abu Dhabi reefs were previously described as a ‘generalist strain’ that is usually not found in corals exposed to high levels of heat stress.”

“The system seems to be more complex than it is commonly thought but now we are in an excellent position to tackle these important questions.”

The Natural Environment Research Council (NERC) has recently granted funding to Dr Wiedenmann and the Coral Reef Laboratory, so that the team can do just that. The researchers will build on their previous findings and use their model corals to investigate the molecular mechanisms that allow corals to thrive at extreme temperatures.