Clock gene and moonlight help corals to co-ordinate a mass annual orgy

Every month, at the full moon, tourists and students gather on the beach at Koh Phangan, Thailand for a night of booze, dancing, and debauchery. But the moon-themed antics of these party-goers look positively tepid when compared to those of the Great Barrier Reef’s corals. With the help of two genes and a spot of moonlight, the corals synchronise one of the greatest spectacles of the natural world – a mass annual orgy.

When it comes to sex, corals play a numbers game. Encased in their rocky shells, direct contact is out of the question so they reproduce by releasing millions of eggs and sperm directly into the surrounding water.

This strategy only makes sense if all the corals release their sex cells en masse and sure enough, every individual within a third of a million square kilometres of reef does so during the days after the October full moon.

The corals’ co-ordination would put even the most organised flash-mobs to shame and until now, scientists had no idea how they did it, especially with neither eyes nor brains. Aside from the obvious contribution of moonlight, the only other available clue was that corals seem to be especially sensitive to blue light.

Bleached corals recover in the wake of hurricanes

Hurricanes can physically cool coral reefs but they can also save them, by cooling the surrounding ocean and reversing the effects of bleaching.

In 2005, corals in the large reef off the coast of Florida were saved by four hurricanes. Tropical storms seem to be unlikely heroes for any living thing. Indeed, coral reefs directly in the way of a hurricane, or even up to 90km from its centre, suffer serious physical damage. But Derek Manzello from the National Oceanic and Atmospheric Administation has found that corals just outside the storm’s path reap an unexpected benefit.

Hurricanes can significantly cool large stretches of ocean as they pass overhead, by drawing up cooler water from the sea floor. And this cooling effect, sometimes as much as 5°C, provides corals with valuable respite from the effects of climate change.

Rising temperatures, dying corals

As the globe warms, the temperature of its oceans rises and that causes serious problems for corals. Their wellbeing depends on a group of algae called zooxanthellae that live among their limestone homes and provide them with energy from photosynthesis. At high temperatures, the corals eject the majority of these algae, leaving them colourless and starving.

These ‘bleached’ corals are living on borrowed time. If conditions don’t improve, they fail to recover their algae and eventually die. But if the water starts to cool again, they bounce back, and Manzello found that hurricanes can help them to do this.

Together with scientists from the Universities of Miami and the US Virgin Islands, he measured the extent of bleaching in reefs off Florida and the US Virgin Islands over the course of 2005.

By September, both reefs were suffering from equal amounts of bleaching. But while the situation continued to worsen in the storm-free Virgin Islands, the advent of four hurricanes in Florida turned the tide in the reefs’ favour.

Hurricanes vs bleaching

The storms – Dennis, Rita, Wilma and the infamous Katrina – each left behind an imprint of cooler water and the seas within 400km of their paths cooled by up to 3.2°C and stayed that way for up to 40 days. Two weeks after the fourth hurricane, Wilma, had passed, the corals had almost completely recovered.

Manzello’s study shows that the benefits of hurricanes on coral reefs can sometimes outweigh the localised physical wear and tear they cause. The question now is whether this is an isolated incident or a common occurrence.

Manzello isn’t sure. Based on the numbers of bleaching events and hurricane landfalls in Florida since the 19^th century, the odds of both happening at the same time (as in 2005) is about one in seven. But the actual probability is likely to be higher especially since the same factors that cause bleaching, such as warmer water, also encourage the growth of hurricanes.

Even so, it would be extremely foolish to expect hurricanes to bail corals out completely – only conservation projects and addressing rising temperatures can do that.

Reference: Manzello, Brandt, Smith, Lirma, Hendee & Nemeth. 2007. Hurricanes benefit bleached corals. PNAS doi.10.1073/pnas.0701194104.

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Hope for corals – swapping algae improves tolerance to global warming
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Corals survive acid oceans by switching to soft-bodied mode

Biologists fear that the world’s beautiful coral reefs may be early victims of climate change, succumbing to the increasing acidity of the planet’s oceans. But new research provides a small glimmer of hope, by showing that corals may be able to weather the upcoming storm by shifting to a temporary soft-bodied lifestyle.

Climate change is not just about surface warming and glacial melting. The carbon dioxide that human activity is pumping into the atmosphere also dissolves in the world’s oceans, slowly increasing their acidity over time. And that spells trouble for corals.

Corals may seem like immobile rock, but these hard fortresses are home to soft-bodied animals. These creatures – the coral polyps – build their mighty reefs of calcium carbonate using carbonate ions drawn from the surrounding water.

But as the water’s pH levels fall, these ions become depleted and the corals start to run out of their chemical mortar. The upshot is that in acid water, corals find it hard to build their homes.

Scientists have predicted that if carbon dioxide levels double, the reef-building powers of the world’s corals could fall by up to 80%. If they can’t rebuild quickly enough to match natural processes of decay and erosion, the reefs will start to vanish.

Now, Maoz Fine and Dan Tchernov from the Interuniversity Institute of Marine Science, Israel, have found that they have a way of coping with homelessness.

They grew some fragments form two European coral species under normal Mediterrenean conditions, and others in water slightly more acidic, by a mere 0.7 pH units.

Those that spent a month in the acidic tank were quickly transformed. The skeleton dissolved and the colony split apart. The exposed and solitary polyps, looking like little sea anemones, still remained attached to rocky surfaces. When the going gets tough, the tough clearly go soft.

Even without their protective skeletons, they survived for over a year and seemed to be going about business as usual. They thrived, they reproduced normally and they still kept the symbiotic algae that allow them to produce energy through photosynthesis.

And when they were put back in normal conditions, they readily gave up their independence and re-formed both colonies and hard shells.

Fine and Tchernov’s findings suggest that corals may be able to survive upcoming climate changes by adopting soft-bodied, free-living lifestyles. And there is evidence that they have used this trick before.

The hard shells of coral reefs fossilise easily, but the fossil record still has large gaps where no reefs are found. These may represent periods of time when corals were biding their time in their soft-bodied phase instead.

But while this new discovery is cause for hope, it should not be cause for complacency. Even though the corals themselves may persist in another guise, the vast diversity of species that depend on them may go for good if their reefs disappear.

More about corals: 
Bleached corals recover in the wake of hurricanes
Hope for corals – swapping algae improves tolerance to global warming

More about the effects of climate change: 
Icebergs are hotspots for life
When the heat is on, male dragons become female
Climate change responsible for decline of Costa Rican amphibians and reptiles

Reference:  Fine and Tchenov. 2007. Scleractinian coral species survive and recover from decalcification. Science 315: 1811.

Technorati Tags: corals, climate+change, environment, science, coral+reefs, ocean+acidication, science,

Hope for corals – swapping algae improves tolerance to global warming

Corals are under severe threat from climate change as higher temperatures cause them to lose the algae that provide them with energy. But salvation may come in the form of a newly discovered ability of corals to swap their algal partners with strains that can take the heat.

Among all of the world’s animals, the two which have built the largest settlements could not be more different. The champions, humans, are intelligent and mobile, rapidly adapting to new conditions with technology and ever-changing strategies. In contrast, the runners-up, corals, seem unchanging and immobile, spending their lives ensconced in their impressive but stationary reefs. But it now seems that corals may have to adapt quickly in the face of looming extinction, ironically, brought about by humans.

Corals are hugely successful animals. Their reefs have endured across millions of years and today, they cover an area of 280,000 square kilometres, larger than the entire United Kingdom. Their success depends on a partnership with a group of algae called zooxanthellae. Over a million of these lodgers can live in a single cubic centimetre of coral, and they provide their landlords with both colour and energy through photosynthesis.

Despite their benefits, the algae are expensive to maintain. During periods of environmental stress, the corals eject them to make ends meet, losing their colour in the process. These ‘bleached’ corals (below) are free to regain their partners at easier times, but if conditions don’t improve, they die.

This is the doom that they now face as global warming threatens to send oceanic temperatures soaring to record levels. The existence of the corals and the biological riches they support is under severe threat. But new research from by Ray Berkelmans and colleagues at the Australian Institute of Marine Science shows that some corals may be able to buy themselves some extra time by swapping their algal partners.

There are 8 different lineages of zooxanthellae (labelled A to H) and it is becoming increasingly clear that how a coral reacts to its environment depends on which of these groups it harbours. In particular, corals with group D algae seem to be particularly good at dealing with high temperatures, and this might prove to be their salvation.

Berkelmans tested this idea by transplanting 22 colonies of the stony coral (Acropora millipora) from a cool inshore reef on the eastern coast of Australia, to a warmer bay about 400 miles away. The colonies contained group C algae, and within half a year, they had all bleached and seven had died. But a few months later, about half of them had recovered and regained their colour. Every single survivor had replaced their partners with those from group D.

Further experiments revealed that the corals’ ability to tolerate temperature was based almost entirely on their choice of partners, with their own biochemistry had no detectable effect. In this partnership, the algae proved to be the weakest link. The key difference between the various groups lies in the membranes of their chloroplasts – their in-house photosynthesis factories. Those that can take the heat have membranes that are stable across a larger range of temperatures.

It isn’t clear from this study alone whether the ability to evict less hardy tenants is widespread among coral species, or even among other populations of stony coral. Even if it is, it may not be enough. Berkelmans found that corals that made the swap could tolerate temperatures about 1-1.5°C higher. With the temperatures of the world’s oceans set to increase beyond that, the corals are living on borrowed time.

We can only hope that this newly discovered ability of corals to rapidly adapt to environmental change gives us enough time to curb carbon emissions and halt climate change.

More about corals: 
Bleached corals recover in the wake of hurricanes
Corals survive acid oceans by switching to soft-bodied mode

More about the effects of climate change: 
Icebergs are hotspots for life
When the heat is on, male dragons become female
Climate change responsible for decline of Costa Rican amphibians and reptiles
Reference: Berkelmans & van Oppen. 2006. Proc Biol Sci 273: 2305-2312.

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