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Improving Water Quality May Help Save Coral Reefs

August 20, 2012
Image Caption: Low nutrient stress promoted the loss of symbiotic algae (bleaching) in a staghorn coral. Credit: University of Southampton

redOrbit Staff & Wire Reports – Your Universe Online

It has been found that an unevenness of nutrients in reef waters can increase the bleaching vulnerability of reef corals according to Research from the University of Southampton and the National Oceanography Centre, Southampton.

Numerous polyps jointly forming a layer of living tissue that cover the calcareous skeletons make up the corals. Single-celled algae called zooxanthellae, which live within the coral polyps, is what they depend on.

Dependence between the coral animal and the associated zooxanthellae survive in a symbiotic relationship, where the coral supplies the algae with nutrients and a place to reside. Accordingly, the algae offer the coral some products of their photosynthesis, providing them with an important energy source.

Survival in a symbiotic relationship, where the coral supplies the algae with nutrients and a place to live, is the coral animal and the associated zooxanthellae depending on each other.  In turn, the algae offer the coral some products of their photosynthesis, providing them with an important energy source.

High water temperatures can block photosynthetic results in the algal cells causing a build-up of toxic oxygen compounds, which threaten the coral and the outcome can result in a loss of the zooxanthellae.

Photosynthetic reactions in the algal cells can be blocked by high water temperatures causing a build-up of toxic oxygen compounds, which threaten the coral and may result in a loss of the zooxanthellae.

Corals appear white without the algae, a state which is often referred to as ‘bleached’. Coral can die because of the bleaching. Coral reef ecosystems have already had devastating effects due to coral bleaching.

Nutrient enrichment of the water can increase the probability of corals to suffer from heat-induced bleaching according to the study of University of Southampton, which was published in the latest issue of the journal Nature Climate Change.

The growth of zooxanthellae is restricted by the limited supply of nutrients within the coral. This lets the algae transfer a considerable amount of their photosynthetically fixed carbon to the coral, which is necessary for the symbiotic relationship.

When the availability of a specific nutrient decreases compared to the cellular demand, a condition called nutrient starvation, algal growth becomes unbalanced.

“It was found that an increased supply of dissolved nitrogen compounds in combination with a restricted availability of phosphate results in phosphate starvation of the algae. This condition is associated with a reduction in photosynthetic efficiency and increases the susceptibility of corals to temperature and light-induced bleaching,” according to researchers from the University of Southampton based at the Coral Reef Laboratory in the National Oceanography Centre, Southampton

Dr Jörg Wiedenmann, Senior Lecturer of Biological Oceanography at the University of Southampton and Head of the Coral Reef Laboratory, who led the study, says: “Our findings suggest that the most severe impact on coral health might actually not arise from the over-enrichment with one group of nutrients, for example, nitrogen, but from the resulting relative depletion of other types such as phosphate that is caused by the increased demand of the growing zooxanthellae populations.”

Dr Wiedenmann also states: “Our results have strong implications for coastal management. The findings suggest that a balanced reduction of the nutrient input in coastal waters could help to mitigate the effects of increasing seawater temperatures on coral reefs. However, such measures will be effective only for a short period of time, so it is important to stop the warming of the oceans, which will otherwise destroy most of the reefs in their present form in the near future.”

“Finally, our results should help the design of functioning marine reserves.”


Source: redOrbit Staff & Wire Reports - Your Universe Online



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