They are huge, and they are one of the greatest threats to corals.
In New Caledonia, Brut nature followed scientists who intervene in areas infested with crown-of-thorns starfish.
In New Caledonia, Brut nature followed scientists who intervene in areas infested with crown-of-thorns starfish.
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AnimalsTranscript
00:00Here is a Lacanthastere, it is this starfish which, when it is too many, causes damage to the reefs while eating corals.
00:18We left for the spider reef, it is a reef that is half an hour away from Nomea's boat.
00:22It is the small area here, and we detected a Lacanthastere infestation 6 months ago.
00:27Today, we will try to look at the extent of the damage.
00:30Did the Lacanthastere leave behind the corals? Did they eat everything?
00:56A Lacanthastere is very easy to recognize.
00:58It is the only starfish with as many arms as there are more than 5 arms.
01:01It can reach up to 21 or 22.
01:03They are iridescent with venomous spines.
01:05It is very large, it can reach up to 70 cm, and it has quite varied colors.
01:09It goes from red to blue, through the arms.
01:26I take off the Lacanthastere of the coral on which it is fixed.
01:31It comes out, it is its intestine that it spreads on the polyps, on the coral.
01:37It even goes inside the small branches of the coral.
01:41It is its stomach that it exteriorizes, which digests the polyps.
01:49A band of dead coral, in fact, is an area in which there is no more color.
01:56We still see the shape of the coral, the branches, the fingers of the coral, the tabulae.
02:01But the animal, the organism itself, has been threatened by the Lacanthastere,
02:05and there is only the skeleton left.
02:20We can see very well the difference between the part that is still alive,
02:25which has not been touched, and the part that is completely dead.
02:28It is the difference in color between the two, in fact.
02:30LACANTHASTERE
02:46Globally, a third of the reefs of the Pacific zone are affected by the Lacanthastere.
02:51This does not mean that they are strongly affected, but we have detected them.
02:54For example, the Great Barrier Reef.
02:56The 25th, 21% of the Great Barrier Reef has been destroyed in the last 30 years by the Lacanthastere.
03:01We have areas in which we have very few Lacanthastere.
03:04This is the natural level.
03:05And we have areas like here, where the number explodes, without us knowing why.
03:09We will see them later.
03:13LACANTHASTERE
03:21Underwater, I unroll the decameter, which allows us to delimit the area on which we count the Lacanthastere.
03:31Behind me, I take a picture of all the meters.
03:33We took the GPS point.
03:36When we unroll the decameter on the point, we make a state of the place.
03:41This allows us to come back and take the same pictures and see the degradation or improvement of the reef.
04:07How many Lacanthastere did we get?
04:09There were 2 Lacanthastere on the first transect and 8 Lacanthastere on the second.
04:18Lacanthastere, like all species, have a role in their ecosystem.
04:22But it is not always a problem.
04:24It only happens when the density, the number, becomes so important
04:27that they consume the reef faster than the reef regenerates.
04:30I have been working for 12 years now.
04:32And we almost never saw it.
04:34There has been an explosion in recent years.
04:38Last year, there were so many Lacanthastere that they hit each other.
04:43We cannot predict when and why the Lacanthastere explosions will occur.
04:48We have a number of hypotheses, including the warming of the waters
04:52and also the enrichment of nutrients,
04:54in particular the fertilizers that arrive in the coastal waters and feed the Lacanthastere larvae.
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05:17The only solution we have against Lacanthastere,
05:20if we want to limit the pressure on a reef, is to remove them.
05:25In the Pacific, people have been collecting them for a long time.
05:28They will bury or burn them.
05:30We have developed systems where we inject them with a lethal product,
05:33which is much more effective.
05:35It can be lemon juice, it can be vinegar.
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05:57In these cases, we can intervene.
05:59It's a debate, because some institutions, some people,
06:02consider that it's not necessarily very effective.
06:05Everything depends on the area, everything depends on the scale.
06:07And we have shown that on some limited areas,
06:09on the contrary, it could work.
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06:23Nowadays, reefs are subjected to a lot of pressure.
06:26There is, what we know the most, climate change.
06:28So, warming, acidification of other surfaces.
06:31We have pollution problems.
06:33We have problems of overexploitation of reefs.
06:35And when we add on top of LACANTHASTERE,
06:37we are not sure that the reefs can regenerate.
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