The acanthaster, a coral-eating seafish

Brut America

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.

Transcript

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.

05:37LACANTHASTERE

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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.

06:11LACANTHASTERE

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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.

06:39LACANTHASTERE

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