Climate change interacts with pollution and overfishing to make bigger problem for reefs
The combination of climate change and ocean chemistry impart “significant and growing threats” to the world’s coral reefs, according to a report published yesterday.
“Reefs at Risk Revisited” involved 25 research, conservation and educational institutions and took three years. It found that three quarters of coral reefs are currently under threat from impacts such as fishing practices, pollution and coastal development and climate change.
The report concludes that the local processes present the most “immediate and direct risks” to coral reefs. However, it says that
“Coral reefs face a wide and intensifying array of threatsâ?¦ In addition, the global threat of climate change has begun to compound these more local threats to coral reefs in multiple ways”.
The interplay between local and global processes is complex, and the part played by global processes, most particularly seawater warming, should not be overlooked.
Warming seawater and ocean acidification arising from our changing climate particularly pose a serious threat to coral reef health.
Coral reefs consist of colonies of tiny marine organisms living in partnership with algae called zooxanthellae. The algae give the coral their bright colours as well as providing them with food.
When faced with long periods of environmental stress, such as unusually warm seawater or slightly more acidic conditions, the symbiotic algae are expelled from the coral tissue, causing “coral bleaching”.
Although coral reefs can recover from coral bleaching, frequent, extensive and widespread bleaching causes it to die. Ocean acidification also detrimentally affects the ability of coral reefs to form their skeletons.
The report predicts that by 2050 “nearly all” coral reefs will be affected by the combined threats of warming seas and ocean acidification.
Additionally, coral reefs can struggle to keep up with sea level rise, particularly if reef health is already compromised. Storm damage to reefs is common, and ailing reefs can struggle to recover from severe storm damage.
The conclusion that “global” impacts from climate change will interact with local impacts like overfishing or pollution in complex and sometimes unpredictable ways is supported by other recent observations.
Research by Dr Nick Graham and colleagues at the ARC Centre of Excellence in Coral Reef Studies and James Cook University published in Ecology Letters this month found that the pressures of climate change and overfishing can interact to put a single reef system under significantly more pressure.
For example coral bleaching causes habitat degradation, which could alter the biodiversity of reef fish, which could contribute to overfishing.
And a recent study by RW Buddemeier and colleagues, published in the Journal Climatic Change, used a model to investigate future coral reef cover over an area of the eastern Caribbean.
The authors used three scenarios developed by the IPCC and considered the effects of both ocean warming and acidification on the coral. The results make rather bleak reading, predicting that coral cover will drop below 5% by 2035.
Even if the coral reefs are able to develop some resilience, coral coverage drops below the 5% level by 2065. The authors say:
“Additional impacts such as storms or anthropogenic damage could result in declines in coral cover even faster than those projected here.”
Around 275 million people live in the vicinity of coral reefs – and a high proportion of those people depend on the coral reef for their survival. More than two thirds of those “most vulnerable” to reef degradation and loss are in Least Developed Countries (LDCs) including Haiti, Grenada, Philippines, Comoros, Vanuatu, Tanzania, Kiribati, Fiji, and Indonesia.
However, the authors of “Reef at Risk Revised” are keen to stress that all is not lost for coral reefs. One of the principal authors, Lauretta Burke, says
“Coral reefs are valuable resources for millions of people worldwide. Despite the dire situation for many reefs, there is reason for hope. Reefs are resilient, and by reducing the local pressures we can buy time as we find global solutions to preserve reefs for future generations.”