Nemo's home under threat from bleaching and rising temperatures

Reef HQ carpet anemone and clown fish
Sea anemones, home to the clown fish, the charismatic star of 'Finding Nemo', and as many as 27 other species, are facing the same worldwide threat as coral reefs – bleaching and loss due to rising water temperatures.

Research by an international team of marine scientists shows that at least seven of the 10 anemone species suffer from bleaching when water temperatures get too high.

The researchers, from Australia, Saudi Arabia and the USA surveyed nearly 14,000 anemones worldwide and found 4 per cent were bleached. However bleaching rates ranged from 20-100 per cent, following five major bleaching episodes.

Dr Ashley Frisch of the ARC Centre of Excellence for Coral Reef Studies at James Cook University was co-author of the report. '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.

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

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 tiny larvae of marine species such as the orange clownfish use their sense of smell to help find suitable adult habitat. Scientists from James Cook University have found that ocean acidification will impair this sense of smell, which could affect the ability of larvae to find the best habitat to live in. Photo courtesy of Dr Simon Foale, ARC Centre of Excellence for Coral Reef Studies

'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.

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.
They conclude that in some areas, anemone 'population viability will be severely compromised if anemones and their symbionts cannot acclimatise or adapt to rising sea temperatures.

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.'

More at www.plos.org