Corals can sense what's coming

November 17, 2011

Australian scientists have thrown new light on the mechanism behind the mass death of corals worldwide as the Earth's climate warms.

Coral bleaching, one of the most devastating events affecting coral reefs around the planet, is triggered by rising water temperatures. It occurs when the corals and their symbiotic algae become heat-stressed, and the algae which feed the corals either die or are expelled by the coral.

There have been seven major bleaching events globally in the past 30 years, the most recent being in 2010 across the Indian Ocean and Coral Triangle. Australia's Great Barrier Reef has suffered eight events since 1980, the worst being in 2002 when 55% of the total reef area was affected. The frequency of these events appears to be increasing.

Now a team of scientists from the ARC Centre of Excellence for Coral Reef Studies and James Cook University has shown that a complex cascade of molecular signals leading up to the self-inflicted death of corals and their symbiotic algae is triggered as sea water begins to warm.

Working with Acropora corals from the reef at Heron Island, the researchers found the cascade begins at ocean temperatures as much as 3 degrees lower than those normally associated with coral bleaching.

And the process culminates in 'apoptosis' or programmed cell-death - a situation in which living organisms (including corals and humans) deliberately destroy their weakened or infected body cells, effectively a form of 'cell suicide' or amputation designed to protect the organism as a whole.

"Our results suggest that the control of apoptosis is highly complex in the coral-algae symbiosis and that apoptotic cell death cascades potentially play key roles in tipping the cellular life or death balance during environmental stress prior to the onset of coral bleaching," explains lead author Dr Tracy Ainsworth.

"It is also clear that this chain reaction responds significantly to subtle, daily changes in the environment and to sea temperatures which were generally thought till now to have little impact on the function of coral and its symbiotic algae."

Paradoxically, the team's research identified molecular signals both promoting and discouraging programmed cell-death in the corals.

This has led them to a theory that corals respond to the stresses caused by warming sea water by killing off some of the cells, while strengthening others in order to stage a possible recovery after the hot water has moved off the reef and conditions have returned to normal.

"This would explain why some corals are able to recover quite quickly from a bleaching event, if it has not gone too far.

"It is far too early to speculate, but understanding the recovery process for any living organism is always a big help, as human medicine has constantly demonstrated, Dr Ainsworth says.

"The next step in our research will be to see how we can use this new insight into the processes of coral bleaching to understand their recovery mechanisms. We also need to know more about how this process works at lower temperatures, or under varying temperatures.

"That in turn will lead us to explore ways that coral reef managers and users can perhaps minimise other stresses on the reef in order to give it the best possible chance of recovery from bleaching."

However the team cautions that "further study of the tissue function and cellular differentiation and recovery processes in coral is needed before this complicated cell death system can be fully understood".
-end-
The team's paper "Defining the tipping point. A complex cellular life/death balance in corals in response to stress" by Ainsworth TD, Wasmund, K, Ukani L, Seneca F, Yellowlees D, Miller D, and Leggat W is published in the latest issue of Scientific Reports published by Nature.

More information:

Dr Tracy Ainsworth, CoECRS and JCU, 61-7-4781-4442 or 0415253820

Dr Bill Leggat, CoECRS and JCU 61-7-47816923 or 0415253820 Prof David Yellowlees, CoECRS and JCU 61-7-47816248 or 0438164824

Jenny Lappin, CoECRS, +61 7 4781 4222

Jim O'Brien, James Cook University Media Office, 61 (0)7-4781-4822 or 0418-892449

http://www.coralcoe.org.au/

ARC Centre of Excellence in Coral Reef Studies

Related Algae Articles from Brightsurf:

Sprat, mollusks and algae: What a diet of the future might look like
Rethinking what we eat is essential if we hope to nourish ourselves sustainably and mind the climate.

Ocean algae get 'coup de grace' from viruses
Scientists have long believed that ocean viruses always quickly kill algae, but Rutgers-led research shows they live in harmony with algae and viruses provide a 'coup de grace' only when blooms of algae are already stressed and dying.

New science behind algae-based flip-flops
Sustainable flip-flops: A team of UC San Diego researchers has formulated polyurethane foams made from algae oil to meet commercial specifications for midsole shoes and the foot-bed of flip-flops.

Battling harmful algae blooms
In two separate studies, the University of Delaware's Kathryn Coyne is looking at why one species of algae has some strains that can cause fish kills and others that are non-toxic, while examining an algicidal bacterium found in Delaware's Inland Bays that could provide an environmentally-friendly approach to combatting algae blooms.

Algae as living biocatalysts for a green industry
Many substances that we use every day only work in the right 3D structure.

Algae in the oceans often steal genes from bacteria
Algae in the oceans often steal genes from bacteria to gain beneficial attributes, such as the ability to tolerate stressful environments or break down carbohydrates for food, according to a Rutgers co-authored study.

Algae team rosters could help ID 'super corals'
U.S. and Australian researchers have found a potential tool for identifying stress-tolerant ''super corals.'' In experiments that simulated climate change stress, researchers found corals that best survived had symbiotic algae communities with similar features.

Algae shown to improve gastrointestinal health
A green, single-celled organism called Chlamydomonas reinhardtii has served as a model species for topics spanning algae-based biofuels to plant evolution.

How do corals make the most of their symbiotic algae?
Corals depend on their symbiotic relationships with the algae that they host.

Algae as a resource: Chemical tricks from the sea
The chemical process by which bacteria break down algae into an energy source for the marine food chain, has been unknown - until now.

Read More: Algae News and Algae Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.