Finding Nemo: how climate change threatens anemone fish and their homes

ANEMONE fish were made famous by the 2003 film Finding Nemo and play a starring role in the sequel, Finding Dory.

They are well known for their special relationship with anemones, which provide a safe place to call home.

But anemone fish face a number of threats. Some researchers have warned of an increase in the wildcaught anemone fish trade, as happened following Finding Nemo.

Anemones, on which anemone fish depend, are threatened by warming seas in a similar way to corals.

Anemones were affected by the recent coral bleaching on the Great Barrier Reef, which current updates show left a third of coral colonies dead or dying in the north and central parts of the reef. So will Nemo be homeless? There are 28 species of anemone fish. Although some people call this group “clown fish”, technically this name is used for only one species, Amphiprion percula. “Nemo” ( A ocellaris) looks similar, but is actually known as the “false clown fish”.

Although they can survive in aquariums, in nature they rely on anemones for protection from predators.

In return, the resident anemone fish will provide nutrients and defend the anemone from predators such as butterflyfish.

Both the number and size of anemone fish are linked to the size and number of anemones – and vice versa. So any decrease in one partner affects the other.

The collection of anemones and anemone fish for Different types of anemone fish in a bleached environment, above and right. The Red Sea, Indian and Pacific oceans have been affected this year. the aquarium trade has to be managed properly to ensure their future.

They can be easily bred in captivity and this provides a reliable source for aquarium enthusiasts without affecting wild populations.

Ten species are inhabited by anemone fish. The highest diversity occurs in Indonesia, where species outnumber anemones. As a result, dif- ferent species have learnt to share the same anemone.

In most other locations, anemone fish aggressively prevent other species from entering their anemone. Anemone fish species differ in the number of anemone species they associate with.

Clark’s anemone fish ( A clarkii) can live in all 10 species and is widely distributed throughout the Indian and Pacific oceans.

In contrast, McCulloch’s anemone fish ( A mccullochi) inhabits only one species and occurs only on reefs around Lord Howe Island, a volcanic remnant in the Tasman Sea between Australia and New Zealand.

After hatching, anemone fish larvae use their keen sense of smell to find their preferred anemone species and avoid unhealthy (bleached) varieties.

Anemones are closely related to corals and get their colour from microscopic algae (zooxanthellae) that live symbiotically within the tissue of the anemone.

Like corals, anemones expel their algae and turn white when they become stressed.

This process – termed “bleaching” – is usually in response to periods of elevated seawater temperatures.

All anemones are susceptible to bleaching, which can result in a decrease in the size and number of anemone fish and reduced reproduction.

If seawater temperatures remain high for too long, then bleached anemones will die. In 1998, a prolonged period of elevated water temperatures in Japan resulted in mass mortality of bleached anemones and local extinction of anemone fish.

Temperature

In March 2016, the Great Barrier Reef experienced a severe bleaching event due to elevated water temperatures associated with a strong El Niño event.

There was mass bleaching of both corals and anemones.

In April 2016, elevated water temperatures also caused mass bleaching of corals and anemones off north-west Australia, including Christmas Island.

Bleached anemones have also been reported elsewhere recently – in the Pacific Ocean, Indian Ocean and in the Red Sea.

The future of the bleached anemones and their resident anemone fish will depend on how quickly the water temperature returns to normal.

If the temperature drops swiftly, bleached anemones can regain their colour (reabsorb zooxanthellae) and survive.

However, the frequency and intensity of bleaching events is expected to increase as the climate changes. So there are serious concerns about the ability of anemones and anemone fish to cope with rising water temperatures.

Reducing global greenhouse gas emissions will limit subsequent bleaching events and help ensure the future of Nemo and his relatives.

• Jean-Paul Hobbs is a research fellow at the department of environment and agriculture, Curtin University. Ashley J Frisch is a postdoctoral fellow in marine ecology at James Cook University.

Hobbs receives funding from Curtin University and Christmas Island Divers Association. Frisch has received funding from the ARC Centre of Excellence for Coral Reef Studies, James Cook University and the Great Barrier Reef Marine Park Authority. – The Conversation