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The seas around Phuket hold a wealth of marine life including
a diverse range of anemone species. These flowerlike animals
come in many different colours. Anemones are found from the
edge of the beach at low tide to depths of less than 20m.
They do not live deeper than this because they contain' Zooxanthellae'.
These are microscopic organisms similar to algae. They photosynthesize
and provide the anemone with most of its nutritional requirements.
Zooxanthellae also produce much of the colour that anemones show.
If an anemone is kept in very low light conditions, the Zooxanthellae
die or evacuate in search of a better home,
just as happens with corals when the water temperature rises
to high. The result is a white anemone (or coral) that will
slowly starve to death even if fed. Small of fishes or prawns
will be accepted by the tentacles and be slowly moved towards
the central mouth, where they are ingested and after a couple
of days excreted though the same opening.
Flesh alone is not enough to sustain anemones. They need the vitamins
manufactured by the Zooxanthellae. All corals need these. Anemones
can be thought of as a coral polyp without a calcium carbonate exoskeleton.
The structure is fundamentally the same in all Coelenterates
The anemones we see at the beach, exposed at low tide, are mainly
brown but amongst the coral many small species can be found in a
range of colours. Some are quite remarkable with colourings such
as apple green with purple streaks, measuring up to 4" (or
10cm) across when fully expanded. Anemones expand and contract by
pumping water in or out of themselves. As they do so larval Zooxanthellae
are sucked in or blown out along with various body wastes.
Sea anemones reproduce by'budding'. Small anemones form below
the disk on the side of the column. When large enough they detach
and float away to fine a new place to live. If its not to their
liking they will detach, float off and try again.
Anemones have been kept alive at public aquariums for over
30 years. Estimates of their life span are up to 70 years
or more. Some Pacific specimens have been found with a diameter
of over a metre.
Nothing seems to eat them; they are all stings and slime. They
inside is just mush. However the islanders of Koh Samui do eat one
species. By wading knee deep at low tide, they collect a very beautiful
species that lives just offshore. This species comes in a variety
of colours, bright yellow or green being the most common. The anemones
are dried in the sun before being added to various recipes. Fortunately,
conservation laws have been introduced and this practice is fading
away. In Thailand at least, anemones are not at risk, as they cannot
be exported for the aquarium trade anymore.
Anemones catch their prey by using nematocysts. These stinging
tentacles work by having a small barbed arrowhead attached to a
thread that is coiled like a spring. When pushed against, these
sting cells release their arrows and capture the intruder, if small
enough. Larger animals break free. The stings from species around
Phuket are not to bad but Caribbean species can be quite dangerous.
Different people have varying degrees of sensitivity to the stings.
This writer can handle local anemones and suffer only minor skin
irritation for a few days. Some people have huge purple marks and
broken skin for up to 2 weeks afterwards. Experimentation is not
advised.
The best-known anemones in the vicinity of Phuket are the large
purple species; Heteractis magnifica 25 - 30 cm in diameter. These
are home to the common anemone fish or clown fish, Amphiprion ocellaris.
The Thais call them cartoon fish for obvious reasons.
These beautiful small fish are only about 7cm long and lay their
eggs on the side (column) of the anemones and guard them. Small
groups of clownfish of every size'hover' above their host. If danger
threatens or a diver approaches too near, they dive in amongst the
tentacles for protection. They have an extra thick layer of mucus
to protect them from the stings and are resistant to the toxins
used in the stings. However, the anemones are also adapted to the
fish and recognizing their mucus, tries not to sting them. If the
mucus is wiped of by a scientist, as in an experiment, the released
fish is killed by the anemones as soon as it seeks protection in
its former home.
The purple green-fingered anemones used by the common clownfish
are mainly found in coral reefs or, as at Hin Muang, they can be
the dominant species and actually fight off corals. Other species
of anemone fish live in different types of anemone. The Seabee clowns
with their black and white stripes can grow to 5inches and live
on top of sand anemones such as Heteractis aurora or Stoichactis
gigas. Only their surface disk, 8 - 16 inches in diameter, is kept
above the sand. These anemones bury their column and can contract
rapidly by ejecting water from within there body cavity and pull
their shrunken disk down below the surface when disturbed e.g. when
a shark decides to lie on that particular spot!
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A group of Ampiphrion sebae the yellow-tailed clown fish or Ampiphrion
clarkii, hover over their chosen home. When threatened, their leader,
the brood female, dives headfirst into the mouth of the anemone.
This causes it to rapidly contract and fold its disk, the smaller
clowns dive into the folds to wait for the danger to pass. Though
the disks are mainly brown or grey these buried parts are a bright
orange-red colour. The columns, hidden in the sand, go down 6 -
10 inches to anchor the anemone by its basal disk, which grips onto
pieces of buried coral.
Phuket has three other species of clown fish; the skunk clown which
is pinkish with a white dorsal line and two species of tomato clown.
Each has its own niche and they are seldom found together. Anemones
are also home to some species pf commensal shrimp. Commensal describes
a mutually advantageous relationship. These small shrimps such as
Periclimenes brevicarpalis are largely transparent with a few patches
of white and purple. They provide a service to the anemone by keeping
it clean and receive protection in return. It is not known quite
how they avoid being stung and eaten by their host?
Anemones are also hosts to an amazing species of porcelain crab,
Neopetrolisthes maculatus. At only about 12 mm across the carapace,
or shell, these crabs have two legs modified to be sweep nets and
they sit on top of the disk'sweeping' the water as it flows past.
Fish don't try to catch them, as the anemone would sting their
face. Where the anemone's advantage lies in this relationship
is hard to see. Possibly they lull small fishes into a false sense
of complacency that ends with the fish becoming the anemones dinner!
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