Nutrients fuelling problem of coral bleaching

| 22/08/2012

coral_bleaching_250373.jpg(CNS): New research from the University of Southampton and the UK's National Oceanography Centre points to an imbalance of nutrients in reef waters as one of the causes of corals susceptibility to bleaching. In common with the rest of the Caribbean region, the problem of bleaching has been identified throughout the Cayman Islands ocean environment. In 2009 local researchers from the Department of Environment reported that nearly all corals in the shallow reefs to about 30 feet now show signs of moderate to severe bleaching, with around 80% of corals in the deeper reefs exhibiting the early signs.

Although the DoE said bleaching is closely associated with global warming, they are also aware that other issues are at play, as revealed by this latest research. The University of Southampton study, published in the latest issue of the journal Nature Climate Change, has found that nutrient enrichment of the water can increase the probability of corals suffering from heat-induced bleaching.

Dr Jörg Wiedenmann, Senior Lecturer ofBiological Oceanography at the University of Southampton and Head of the Coral Reef Laboratory, who led the study, said the findings suggest that the most severe impacton coral health might be from the depletion of phosphate that is caused by the increased demand of algae populations.

"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,” he said.

Corals are made up of many polyps that jointly form a layer of living tissue covering the calcareous skeletons. They depend on single-celled algae called zooxanthellae, which live within the coral polyps.

The coral animal and the associated zooxanthellae depend on each other for survival in a symbiotic relationship, where the coral supplies the algae with nutrients and a place to live. 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 reactions in the algal cells, causing a build-up of toxic oxygen compounds, which threaten the coral and can result in a loss of the zooxanthellae.

Without the algae, corals appear white, a state which is often referred to as 'bleached'. Bleaching often leads to coral death and mass coral bleaching has had already devastating effects on coral reef ecosystems.

Within the coral, the growth of zooxanthellae is restricted by the limited supply of nutrients. This allows the algae to transfer a substantial amount of their photosynthetically fixed carbon to the coral, which is crucial for the symbiotic relationship.

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

Researchers 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.

Wiedenmann said balancing the nutrients in the oceans may help but it was important to stop the warming of the oceans, which will otherwise destroy most of the reefs in their present form in the near future. However, he said the results should help the design of functioning marine reserves in the short term.

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  1. Green Hornet says:

    The problem with deep well septic disposal is that the nutrients still leach into the ocean surrounding the island – hence the massive algae blooms in recent years. Once again we copied Florida with environmentally destructive planning guidelines and legislation. The first time was with canals – which Florida stopped approving and building more than a decade ago because they funnel storm surge from hurricanes (as we discovered during Ivan). The second was deep well sewage disposal, which Florida also stopped mandating several years ago.

    I have never understood why we blindly copy things that the US does and then continue to do them long after they have figured out that they are environmentally destructive.

    • Anonymous says:

      You can't blame the wells until you stop the direct raw sewerage discharge pipes that are grandfathered in all over the island. Not to mention the Turtle Farm outflow, Mount Trashmore runoff, golf course fertilizer, etc.

  2. Anonymous says:

    Just take a dive near the turtle farm outlets and the dolphin torture park if you want to see the effects of nutrient bleaching

  3. Anonymous says:


    Wonder if this might be a result of over 80% of our island's sewage trickling down into deep wells, or not so deep wells for that matter? From studies done by the Water Authority septic tanks and other onsite treatment systems are discharging relatively untreated sewage into our ground water. 

    This serious problem was first identified in 2003 and again studied in 2009. From the WAC's findings it does seem as if the problem is getting worse as our population grows.

    Water Authority’s own law is mandates them to mitigate this problem but have they yet addressed the weaknesses in managing the problem.

    For years well drillers have been handed licences to drill septic and water wells without proper due diligence. Inspections on wells or drilling practices are for the most part never performed until damage is already done. Violators, if identified get a slap on the wrist, so it is safe to say that enforcement of proper drilling practices and onsite treatment system scheduled maintenance is nil. Blame it on lack of staff, budget, or more to the point lack of management initiative. Be careful; don’t open a can of worms you may have to do something about it for once.

    Only the WAC has the legal power and responsibility to properly manage any source of contamination originating on land that finds its way into our territorial waters. Why the apathy??

    If anyone cares understand more read these:




  4. Anonymous says:

    Nice find, CNS. I wonder if these folk are going to suggest that we start dumping synthetic chemicals in the water to offset said imbalance?

    It's no wonder we are riddled with disease, cancer and allergies. Unfortunately if you get a bunch of boffins funded by the UN, they will conclude whatever the UN wants them to conclude.

    • Kung Fu Iguana says:

      Yes, that deep-seated neo-con fear of the UN, as sensible as denying global warming and advocating the benefits of easy gun access.

  5. Anonymous says:

    I have great respect for Southampton University's Oceanic Department and the National Oceanography Centre but in the case of the Cayman Islands their findings need to be qualified.

    Most of the worst coral damage I've seen in the Cayman Islands can be directly attributed simply to sand and other debris that has run off from ill-considered and poorly-executed developments along the shore-line. In simple terms the coral has died because no one bothered to factor in the effects of building solid structures on a beach.

    Strange as it may seem coral and sand do not mix. If you build anything that waves can break up against and wash sand from a beach out into the sea that sand will quickly clog the coral and kill it. Coral bleaching is, with property management, often reversible but the effects of sand, concrete dust and other similar materials is not.