Saving Nemo: how climate change threatens anemonefish and their homes

Jean-Paul Hobbs, Curtin University and Ashley J Frisch, James Cook University

Anemonefish, or clownfish, were made famous by the 2003 Disney-Pixar film Finding Nemo, and are about to 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 anemonefish face a number of threats. Some researchers have warned of an increase in the wild-caught anemonefish trade, as happened following Finding Nemo.

Anemones, on which anemonefish depend, are threatened by warming seas in a similar way to corals. In fact anemones were affected by the recent coral bleaching on the Great Barrier Reef, which recent updates show has left a third of coral colonies dead or dying in the north and central parts of the reef.

So will Nemo be left homeless?

A healthy (left) and bleached (right) bubble-tip anemone (Entacmaea quadricolor) on the Great Barrier Reef.
Ashley Frisch

Nemo and his 27 cousins

There are 28 species of anemonefish. Although some people call this group “clownfish”, technically this name is only used for one species, Amphiprion percula. “Nemo” (A. ocellaris) looks similar, but is actually known as the “false clownfish”.

Anemonefish are famous for their special relationship with anemones. Although they can survive in aquariums without anemones, in nature they rely on anemones for protection from predators.

The pink anemonefish (Amphiprion perideraion) in a bleached anemone (Heteractis magnifica) at Christmas Island.
JP Hobbs.

In return for providing a safe home, the resident anemonefish will provide nutrients and defend the anemone from predators such as butterflyfish. Both the number and size of anemonefish is linked to the size and number of anemones – and vice versa. Therefore, any decrease in one partner affects the other.

The collection of anemones and anemonefish for the aquarium trade has to be managed properly to ensure the future of anemonefishes. Anemonefish can be easily bred in captivity and this provides a reliable source for aquarium enthusiasts without impacting wild populations.

Cinnamon anemonefish (Amphiprion melanopus) in a bleached anemone (Entacmaea quadricolor) on the Great Barrier Reef.
Ashley Frisch

Ten species of anemones are inhabited by anemonefish. The highest diversity of anemonefish occurs in Indonesia, where anemonefish species outnumber anemones. As a result, different species of anemonefish have learnt to share the same anemone.

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

Clark’s anemonefish (Amphiprion clarkii) in a bleached anemone (Cryptodendrum adhaesivum) at Christmas Island.
JP Hobbs.

Clark’s anemonefish (A. clarkii) can live in all ten anemone species and is widely distributed throughout the Indian and Pacific Oceans. In contrast, McCulloch’s anemonefish (A. mccullochi) inhabits only one species of anemone and occurs only on reefs around Lord Howe Island.

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

Anemones in hot water

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 ten species of anemones are susceptible to bleaching, which can result in a decrease in the size and number of anemonefishes and reduced reproduction.

McCulloch’s anemonefish (Amphiprion mccullochi) in a bleached anemone (Entacmaea quadricolor) at Lord Howe Island.
Justin Gilligan.

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 anemonefish.

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.

Marine biologist Jean-Paul Hobbs studying anemonefish (Amphiprion mccullochi) and their host anemones (Entacmaea quadricolor) at Lord Howe Island.
Justin Gilligan.

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 recently been reported elsewhere in the Pacific Ocean, Indian Ocean and in the Red Sea.

The future of the bleached anemones and their resident anemonefish will depend on how quickly the water temperature returns to normal. If the temperature decreases swiftly, bleached anemones can regain their colour (reabsorb zooxanthellae) and survive.

However, the frequency and intensity of bleaching events are predicted to increase as the climate changes. Consequently, there are serious concerns about the ability of anemones and anemonefish to cope with rising water temperatures.

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

Jean-Paul Hobbs, Research Fellow, Department of Environment and Agriculture, Curtin University and Ashley J Frisch, Postdoctoral Fellow in Marine Ecology, James Cook University

This article was originally published on The Conversation. Read the original article.

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Ten years on: how Al Gore’s An Inconvenient Truth made its mark

John Cook, The University of Queensland

Ten years ago, An Inconvenient Truth opened in cinemas in the United States.

Starring former US vice president Al Gore, the documentary about the threat of climate change has undoubtedly made a mark. It won two Academy Awards, and Gore won the 2007 Nobel Peace Prize for his efforts to communicate human-induced climate change.

An Inconvenient Truth (AIT for short) is the 11th-highest-grossing documentary in the United States. According to Texan climatologist Steve Quiring:

AIT has had a much greater impact on public opinion and public awareness of global climate change than any scientific paper or report.

But has the film achieved what it set out to do – raise public awareness and change people’s behaviour in order to reduce greenhouse gas emissions?

Measuring the film’s impact

A public survey by the Pew Research Center for People & the Press found that in the months following the documentary’s release, the percentage of Americans attributing global warming to human activity rose from 41% to 50%. But how do we know whether AIT contributed to this increase?

Several studies have experimentally tested the impact of viewing the film. A UK study found that showing selective clips from AIT resulted in participants feeling more empowered and more motivated to make lifestyle changes to fight climate change.

Similarly, surveys of moviegoers and students found that watching AIT increased knowledge about the causes of global warming and willingness to reduce greenhouse gases. However, this increased willingness didn’t necessarily translate into action. A follow-up survey conducted a month later found little change in behaviour.

One novel approach found a 50% increase in the purchase of voluntary carbon offsets in areas where AIT was shown. This is encouraging evidence that the film did lead to tangible behaviour change. But again, the effect wasn’t long-lasting. A year later, there was little difference in carbon offset purchases.

An analysis of drivers of public attitudes towards climate change found a significant relationship between media mentions of AIT and public perception of the urgency of climate change. In other words, the film produced a significant positive jump in the general public’s perceptions of the issue.

This study also found that polarisation decreased after the release of AIT, pouring cold water on the claim that Al Gore polarised the climate debate. Rather, the polarised positions on climate science among Democratic and Republican leaders (one party broadly accepting the science, the other significantly rejecting it) was found to be the key driver of public polarisation on climate change.

This led the study’s author, Robert Brulle, to state:

I think this should close down forever the idea that Al Gore caused the partisan polarisation over climate change.

This body of research underscores the difficulties confronting any public awareness campaign. AIT was successful in raising public awareness of climate change, increasing willingness to change behaviour and, in some cases, actually changing behaviour.

However, the effect didn’t last long. This indicates that persistent communication efforts are required to promote sustained behaviour change.

Scientists critique An Inconvenient Truth

While AIT was effective among the general public, there is no tougher crowd for a science documentary than scientists. A survey of members of the American Meteorological Society and the American Geophysical Union found that among the scientists who had seen and rated AIT, 72% said the film was either somewhat or very reliable.

To put this in perspective, only 12% of scientists who had read Michael Crichton’s contrarian novel State of Fear rated it as somewhat or very reliable.

Going into more detail, an edition of GeoJournal had four scientists critique the scientific accuracy of AIT. Unfortunately, the panel was made up of two mainstream scientists and two contrarian scientists – a false-balance form of coverage that actually causes confusion rather than increases literacy in the context of media coverage. (For an incisive look at false-balance coverage of climate change, watch John Oliver’s statistically representative climate change debate.)

A statistically significant climate change debate

The outcome is somewhat predictable, with mainstream scientists reporting a more positive assessment of the accuracy of AIT than the contrarian scientists. Nevertheless, a useful overview of the exercise is provided by Texan climatologist Gerald North, who concluded that while there were some inaccuracies in AIT, on the whole it represented mainstream scientific views on global warming.

Ultimately, the factual inaccuracies in AIT were deemed inconsequential and don’t undermine the main message of the film.

Inspiring others

While most of the research into the impact of AIT investigates the direct effect on viewers, a potentially more significant impact is the film’s role in inspiring others to follow Gore’s example in communicating the issue of climate change to others.

Personally, I can attest to this influence. Before 2006, I hadn’t given much thought to the climate change issue. Watching AIT raised a number of questions about the human role in global warming.

With the issue salient in my mind, I got into conversations with family members who happened to reject the scientific consensus on climate change. This precipitated the founding of Skeptical Science, which led to me becoming a researcher in climate communication at the University of Queensland.

I’ve spoken to or know of many other climate communicators whose awareness of the issue dawned with their viewing of AIT. While the direct effect of the original screening of the film may have dissipated, the impact of those inspired to communicate the realities of climate change persists.

For me, the film precipitated a series of events that ultimately redirected the course of my life. An Inconvenient Truth wasn’t just behaviour-changing, it was life-changing.

No lab experiment can quantify that level of impact.

John Cook, Climate Communication Research Fellow, Global Change Institute, The University of Queensland

This article was originally published on The Conversation. Read the original article.