Scientists warn sea anemones are vulnerable to bleaching

The World Today Stephanie Smail ABC News 20 Aug 13;

An international research team is warning that sea anemones are bleaching on a large scale.

The anemones are home to 28 species of fish, including the clownfish, which could also be at risk.

Researchers from the United States, Saudi Arabia, Australia and France surveyed 14,000 sea anemones from the Red Sea to the Pacific Ocean and found huge patches of the usually vibrant coral had bleached white.

While scientists have been studying coral bleaching for years, this is the first time a study has focused solely on whether or not anemones are bleaching too.

The study looked specifically at the species of sea anemones that shelter fish.
Audio: Are sea anemones bleaching? (The World Today)

It found seven out of 10 are vulnerable to bleaching and in some places entire anemone beds had turned white.

Dr Ashley Frisch from the ARC Centre for Excellence for Coral Reef Studies at James Cook University says the researchers were alarmed by what they found.

"Normally anemones are relatively brightly coloured, they're rich in colour," he said.

"They can be brown, they can be pink or purple. They're just always rich in colour. A normal, healthy anemone is never white.

"What we find is when you go to places where there's been an increase in temperature in recent times the anemones are white like a piece of paper and that is not normal.

Dr Frisch says sea anemones living in Australian waters were not the worst affected and the Great Barrier Reef only had small patches of bleaching.

"In some places anemones form a significant proportion of the habitat or the cover of the sea floor," he said.

"In some places it's measured on a scale of tens of metres squared where you'll just be [seeing] enormous patches of white where the anemones have bleached.

"It's not like that on the Great Barrier Reef, fortunately. It's more isolated cases. But in some other places of the world where there's a significant and sustained increase in temperature, we've seen vast fields of anemones become bleached."

Dr Frisch says there is evidence some anemones can survive bleaching and recover but there is also a risk some will die off.

He says that poses a risk to 28 species of anemone fish that can not survive anywhere else.

"They might [survive] in an aquarium, but out there in the wild you never see anemone fish without an anemone," he said.

"The simple reality is without them they are exposed to predation and they just get eaten. We've done experiments to prove this. We've covered up an anemone and deprived the anemone fish of access to its house and very quickly that anemone fish gets eaten.

"We've also captured them and translocated them to a different place, dozens of metres away and within a very short time they just get eaten. So they are really dependent on that anemone for their survival."

The short-term study did not reveal exactly what is causing the bleaching.

Dr Frisch says that is the next step for him and his colleagues, along with finding out how the bleaching impacts anemone fish.

"Why is it that fish on bleached anemones appear skinny? Why do they decline in number? And what are the long term consequences for the fish?" he said.

"And of course, that has flow on effects for the aquarium trade and for the wellbeing of lots of fisherman who catch anemone fish for their livelihoods."

'Nemo' won't go home
Science Alert 21 Aug 13;

Round the planet the loveable clownfish Nemo may be losing his home, a new scientific study has revealed.

Research by an international team of marine scientists has found that sea anemones, which provide shelter for clownfish and 27 other fish species, are facing the same worldwide threat as coral reefs – bleaching and loss due to rising water temperatures.

“Our study showed that at least seven of the ten anemone species suffer from bleaching when water temperatures get too high,” says Dr Ashley Frisch of the ARC Centre of Excellence for Coral Reef Studies at James Cook University, a co-author of the report which has highlighted a potential crisis for two of the world’s most popular marine species.

“Importantly, we found bleaching of anemones occurring wherever we looked – from the Red Sea and Indian Ocean to the Indo-Australian region and the Pacific. Sometimes it was on a massive scale.”

The bleaching appears to be due to the same cause as coral bleaching – loss of the anemone’s symbiotic algae, which supply an important part of its nourishment. This happens when the surrounding water becomes too warm.

But it also involves the loss of the brightly coloured fishes which the anemone protects – and which in turn protect it. The result is a collapse in the delicate three-way partnership between algae, anemone and fish.

“Anemones are naturally tough and live for many years. As a result their rates of reproduction are slow – and when they are hit by a killer bleaching event, it can result in their complete loss from an area over a period of time. It appears they cannot reproduce fast enough to make good the loss, especially if the fish are also gone,” Dr Frisch explains.

“Bleaching causes the loss of anemonefish, like nemos, which have nowhere to hide and without the anemones to protect them are quickly gobbled up by predators.

“Also, because the fish appear to perform useful services for the anemone like protecting them from grazing fish, it may also be that the loss of anemonefishes following a bleaching event means the anemones themselves are much less likely to recover.”

The researchers, from Australia, Saudi Arabia and the USA surveyed nearly 14000 anemones worldwide and found 4 per cent were bleached. However bleaching rates ranged from 20-100 per cent, following five major bleaching episodes.

They conclude that in some areas, anemone “population viability will be severely compromised if anemones and their symbionts cannot acclimat(is)e or adapt to rising sea temperatures.

“Anemone bleaching also has negative effects to other species… including reductions in abundance and reproductive output of anemonefishes.

“Therefore, the future of these iconic and commercially valuable coral reef fishes is inextricably linked to the ability of host anemones to cope with rising sea temperatures associated with climate change.”

The study concludes “If host anemones (and their symbiotic algae) cannot acclimate or adapt to rising sea temperatures, then populations of host anemones and associated anemonefishes are anticipated to decline significantly.”

Dr Frisch says that apart from their roles in coral ecosystems, anemones and their fish are of economic importance to both tourism and the aquarium trade, and many poor coastal communities depend on the income they bring.

The report “Taxonomic, Spatial and Temporal Patterns of Bleaching in Anemones Inhabited by Anemonefishes’ by Jean-Paul A. Hobbs, Ashley J. Frisch, Benjamin M. Ford, Michele Thums, Pablo Saenz-Agudelo, Kathryn A. Furby and Michael L. Berumen appears in the journal PLOS One.