SpecieS and climate change: - IUCN

ClownfiSh and Climate Change
Clownfish (family: Pomacentridae), also known as
anemonefish, are some of the most iconic marine fish in
the world. They are highly popular among SCUBA divers
due to their striking colour combinations of white, orange,
yellow and brown.
There are a total of 28 species of clownfish, which are all
very similar in their habits. Perhaps the most renowned
of these is the Common Clownfish (Amphiprion ocellaris),
which was popularised in the Walt Disney movie ‘Finding
Nemo’.
what do we know about clownfish?
Clownfish are found in tropical and subtropical areas of
the Pacific and Indian Oceans. The greatest diversity of
clownfish is found close to Papua New Guinea, although
the Great Barrier Reef in Australia is also known for a
number of unique variants.
Within their range, clownfish are restricted to shallow
waters due to their fascinating relationship with only a
handful of specific sea-anemone species upon which
they depend. While most fish are repelled by the
anemones’ poisonous stings, the clownfish acquires
immunity to this defence, and is therefore able to use
it for its own protection against predators. In return,
clownfish keep their host anemone in a healthy state, and
prevent them from being attacked by angelfishes and sea
turtles, (which are also immune to the sea anemone’s
stinging tentacles).
A single sea-anemone may support several clownfish,
all of which, excluding one single female, are males at
various stages of development. Should the sole female
die, then the largest male turns into a female and
continues breeding.
Clownfish lay their eggs beneath the oral disc of their
host sea anemone and these are guarded by the male.
When the eggs hatch, larvae are carried away by ocean
currents and most perish.
As a larva develops, it begins to use chemical signals
present in the water to detect a suitable anemone to be
used as its new home. These signals permit the young
fish to select the right type of anemone, and ensure that it
is different from its place of birth to avoid inbreeding. The
period between hatching and seeking a new anemone
‘home’ is notably short (around 8–12 days), meaning
that they do not disperse very far from their parents’
anemone.
how is climate change affecting clownfish?
The most significant impacts of climate change on
clownfish are those affecting their coral reef habitat, and
water temperature and chemistry. Such changes may
affect clownfish in a number of ways.
Loss of habitat as coral reefs decline:
At today’s level of 387 ppm CO 2 , coral reefs are seriously
declining and time-lagged effects will result in their
continued demise. If CO 2 levels are allowed to reach 450
the iUCn Red list of threatened Species
ppm (due to occur by 2030–2040 at the current rates
of increase), reefs will be in rapid and terminal decline
world-wide from multiple synergies arising from mass
bleaching, ocean acidification, and other environmental
impacts (more details are available in the staghorn coral
account).
© Alfonso Gonzalez
Clownfish depend on sea-anemones, which are most
frequently found on coral reefs. Reef-dependent species
such as the clownfish will undoubtedly be affected by the
decline in coral reefs. In 1998, one of the most severe
global coral bleaching events in recorded history led to
the complete disappearance of several sea-anemone
species used by clownfish in the corals reefs around
Sesoko Island, Japan, causing local population declines.
Disruption of navigation as ocean acidity rises:
Increases in ocean acidity levels have been shown to
affect clownfish’s ability to detect the chemical signals
necessary for navigating to and locating their anemone
homes. This effect is known to be particularly severe
in juvenile fish. Fish that are unable to locate a suitable
hiding place are at a much higher risk of predation, and
are much less likely to find other clownfish with which to
mate.
Juvenile fish that are unable to locate new anemones to
inhabit also have a much greater chance of returning to
their original place of birth. While such individuals may be
considered fortunate for at least finding protection, the
likelihood of inbreeding in these fish is greatly increased.
Adult clownfish, although less susceptible to the loss of
chemical cues, can still become confused and lost when
venturing away from their host anemone. An extended
period away from their host commonly leads to the loss