Butterflyfish May Face Extinction


February 25, 2008

A beautiful black, white and yellow butterflyfish, much admired by
eco-tourists, divers and aquarium keepers alike, may be at risk
of extinction, scientists have warned.

The case of the Chevroned
Butterflyfish is a stark example of how human pressure on the world’s
coral reefs is confronting certain species with“blind alleys” from
which they may be unable to escape, said Morgan Pratchett, a
postdoctoral research fellow at the ARC Centre of Excellence for Coral
Reef Studies and James Cook University.

In a study published in the journal Behavioural Ecology and Sociobiology, Pratchett
and Michael Berumen, a postdoctoral scholar in the biology department of
the Woods Hole Oceanographic Institution, warn that the highly
specialized nature of the feeding habits of this
particular butterflyfish – the distinctively patterned Chaetodon trifascialis
make it an extinction risk as the world’s coral reefs continue
to degrade due to human over-exploitation, pollution and climate change.

“The
irony is that these butterflyfish are widespread around the world, and
you’d have thought their chances of survival were pretty
good,” Pratchett said. “But they only eat one sort of coral – Acropora hyacinthus – and when that runs out, the fish just disappear from the reef.”

The team found it hard to believe a fish would starve rather than eat a mixed diet, so they tested C. trifascialis in tank
trials on a range of different corals. The fish grew well when
its favorite coral was available, but when this was removed and other
sorts of corals offered, it grew thin, failed to thrive and some died.

“We
call these kinds of fish obligate specialists.  It means they have
a very strong dietary preference for one sort of food, and when that is
no longer available, they go into decline. We still don’t have a
satisfactory scientific explanation for this, as it seems like rather a
risky tactic in evolutionary terms – but it must confer some advantage
provided enough of its preferred food is available,”Pratchett said.

The A. hyacinthus coral,
which the butterflyfish feeds on, is itself highly vulnerable to attacks
by plagues of crown-of-thorns starfish (thought to be triggered by
humans releasing excess nutrients onto the reef as sediment, fertilizer
or sewage), to storms and to the coral bleaching caused by the heating
of ocean surface waters to 32 degrees or more, which is thought to be
linked to global warming.

“Although extremely widespread, the
Chevroned butterflyfish may be at considerable risk of extinction
following ongoing degradation of coral reefs around the world, because
the coral itself is exceptionally vulnerable,” Pratchett said. “It is
estimated that up to 70 percent of the world’s coral reefs are now badly
degraded, which usually involves the loss of this particular coral. And
when it goes, the C. trifascialis also disappear from the reef.”

To
make matters worse, butterflyfishes are one of the main families
of coral reef fishes being targeted by aquarium collectors. However,
the specialized coral-eaters are clearly not suitable for keeping
in aquaria and often die because they cannot obtain their main food
source.

A previous case in which a coral-dependent fish vanished occurred in the case of Gobiodon,a
specialized coral-dweller known only from one site, Kimbe Bay in Papua
New Guinea, which was thought by scientists to have possibly become
extinct after its habitat was destroyed.

Researchers consider
that such extinctions are likely to occur as part of the global mass
extinction of species now taking place, and that marine ecosystems may
be particularly vulnerable in that small changes in habitat or water
quality can have a big impact on their species.

Pratchett and
Berumen said the study is one of the few so far to consider the
evolutionary and ecological basis of dietary versatility, and has
implications for the fate of specialized feeders throughout the animal
kingdom.

Courtesy of James Cook University Media Office.
James
Cook University is Australia’s leading tropical research university.
Areas of research focus include: biodiversity, sustainable management of
tropical ecosystems, global warming, tropical agriculture, tropical
health care in remote communities and cultural diversity.

The
Woods Hole Oceanographic Institution is a private,
independent organization in Falmouth, Mass., dedicated to marine
research,engineering, and higher education. Established in 1930 on
a recommendation from the National Academy of Sciences, its
primary mission is to understand the oceans and their interaction with
the Earth as a whole, and to communicate a basic understanding of
the ocean’s role in the changing global environment.