Although
the Crown of Thorns Starfish (COTS), Acanthaster
planci, is not something to be excited about in the slightest, it is worth
blogging about, as they are quite interesting creatures. There are actually over 2000 different species of
starfish or sea stars. Most have the remarkable ability to consume prey outside
their bodies and they can also regenerate entire limbs! The general consensus
about starfish though, are that they are nice, pretty, colourful little animals, but the COTS is far
from it. The second largest starfish in the world, it has a diameter of up to 3
feet and up to 21 arms! There bright colours make them quite beautiful and nice
to look at, but beneath their fortress of protective poisonous spines is
something quite deadly and destructive.
Crown-of-thorns starfish are one of the most damaging
creatures of tropical coral reefs. They are corallivores, preying on living
coral polyps! COTS especially like to eat the fast- growing Acropora species, particularly table
corals. With hundreds of sucker-like tube feet they climb onto living corals
and then throw out their stomach through their mouth to digest the coral tissue
alive so it can be absorbed! Not so nice! This leaves a white scar of dead
coral skeleton. One starfish can consume up to 6 square meters of living coral
reef per year. Natural numbers of these starfish on the reef are not a huge
problem, however, if there is a huge population boom, whereby their numbers are
increased in their hundreds, well they can ultimately devastate entire reefs.
So it
was not the best news when one of the dive instructors reported seeing many of them on the outside reef of the atoll! What to do? COTS do have natural predators, titan
trigger fish, napoleon humphead wrasse and the huge triton snail, but not so
many on the reef as to eat all the starfish. We decided the best plan of action was
to collect and remove the starfish from the reef before they wipe it out for themselves.
It was the right thing to do. During a 5 minute swim along the reef I counted
300 of them. I have never seen so many before, it was shocking. They had
devoured part of the reef leaving just the white skeletons of dead corals in
the wake of their feeing path. Our mission was on.... we did back to back dives and managed to collect most of the them so not bad for a days work!!
Though scientists do not know for certain what causes COTS outbreaks, there are a number of possibilities:
Though scientists do not know for certain what causes COTS outbreaks, there are a number of possibilities:
- the outbreaks
are part of a natural cycle
- overfishing and
the decline of the starfishes natural predators
- human disturbance such as agricultural run-off of nutrients from land leading to phytoplankton blooms which provide more food for the starfish larvae.
Hopefully that will be the last we see of them for a long time.
COTS devouring a large table coral. The white skeleton is the dead coral and the brown is still living, for the time being anyway!
Mission on - collecting as many as possible. We used fins or sticks to pick them up as they are covered in protective venomous spines which can give a nasty sting
So many on the reef consuming all the coral in their paths. It was heartbreaking :(
Greedy buggers! The coral has no chance...
Their sucker tube like feed to move around with a mouth in the middle
A dead white coral skeleton, Acropora clathrata, which use to be beautiful and alive!
All the dead white coral skeletons. It was like swimming over a grave yard!
Bringing them up to the surface
Whoop whoop, mission accomplished. They dont smell too good on the surface though
We collected about 250 all together. Was a great team effort
great job :)
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