Crown of Thorns is a Symptom of Reef Decline: Let’s Address the Cause

Great Barrier Reef (Photo: Wikipedia)

by Dr Terry Hughes, Federation Fellow, ARC Centre of Excellence for Coral Reef Studies at James Cook University, The Conversation: http://theconversation.edu.au

A recent report on coral loss from the Great Barrier Reef has pointed the finger at cyclones and Crown of Thorns starfish.

The real culprit is human activity, and until we reduce port activity and pollution, coral will be unable to bounce back.

Three recent studies, published in 2004, 2007 and this week, have shown that at least 50% of the corals on the Great Barrier Reef have disappeared in recent decades.

Last year, another report claimed the declines were more modest and the result of a natural cycle. But the latest report, from the Australian Institute of Marine Science, confirms earlier studies - the Great Barrier Reef is in trouble.

Corals are the backbone of the reef, providing habitat for many other species. Measuring coral cover on a reef is the simplest way to monitor its condition.

But other metrics - like counts of sharks, dugongs and turtles - also show alarming downward trajectories. The decline in coral cover highlights UNESCO’s concerns about the dwindling Universal Heritage Values of the Barrier Reef.

The key question now is, what are we going to do about these losses?

First, we need to consider why coral cover changes. The amount of coral goes down when they reproduce less, grow more slowly or die more frequently. Even under ideal conditions, about one-quarter to one-third of a coral population dies each year from background mortality.

They can die from old age, disease, predation, competition with a neighbour, erosion of their skeleton, smothering by sediment, severe coral bleaching, and from storms.

On a healthy reef, loss of cover is balanced by new recruitment of young corals and by new growth. It’s just like a human population - we measure births, deaths and net migration to track demographic changes. Measuring mortality alone won’t help us to plan for schools or new roads.

Next consider where the loss of coral cover is greatest. The 50% decline in coral cover is averaged over the whole Great Barrier Reef (GBR). However, there has been no net loss of coral cover in the remote north beyond Cooktown or on reefs far from shore. Consequently, most reefs that are close to the coast (and to people) have lost far more than 50% of their cover.

To read further, go to: http://theconversation.edu.au/crown-of-thorns-is-a-symptom-of-reef-decline-lets-address-the-cause-9932?utm_medium=email&utm_campaign=Latest+from+The+Conversation+for+4+October+2012&utm_content=Latest+from+The+Conversation+for+4+October+2012+CID_f854c801de6c785bfe260d692fd58edc&utm_source=campaign_monitor&utm_term=Crown%20of%20Thorns%20is%20a%20symptom%20of%20reef%20decline%20lets%20address%20the%20cause