Parasite is causing masses of sea urchins to die worldwide

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The mass extinction of sea urchins caused by a parasite is increasingly becoming a global pandemic. Researchers see this as a threat to the underwater world – especially the coral reefs, which are already suffering greatly from climate change.

The deadly disease has now been discovered in the Indian Ocean, a team of researchers reports in the journal ‘Current Biology’. Images show numerous dead sea urchins on a beach on Reunion Island. The outbreak poses an immediate threat to coral reefs worldwide: sea urchins eat algae that would otherwise overgrow and kill corals.

The Mediterranean Sea has also been affected
In January 2022, a mass death of diadem sea urchins caused by ciliates was noted for the first time in the Virgin Islands. In the following months, similar observations were made in much of the Caribbean. Subsequently, the Mediterranean Sea and soon the Red Sea were also affected.

It is estimated that as of December 2022, most populations of affected sea urchin species in the Red Sea, as well as hundreds of thousands of sea urchins worldwide, have been destroyed. For example, in the reef system near the Israeli coastal city of Eilat, the two species of sea urchins that were previously most common in the Gulf of Aqaba have completely disappeared.

Ciliates are responsible for mass extinctions
A team led by Omri Bronstein of Tel Aviv University has now identified the pathogen responsible for the mass death of common diadem sea urchins (Diadema setosum) – long-spined black sea urchins – in the Red Sea: a ciliate similar to the species Philaster apodigitiformis. The single-celled parasite is also the cause of the mass extinction of the Atlantic diadem sea urchin (Diadema antillarum) in the Caribbean about two years ago.

A devastating population decline was already observed in this region in 1983. Both coral and sea urchin populations in the Caribbean never fully recovered, the scientists report.

It is suspected that the pathogen, which has now been identified, was the cause. According to the researchers, the ciliate also attacks Echinothrix sea urchins, a group of species closely related to Diadema.

Researchers consider coral reefs to be critically endangered
The parasite causes the animals to become a tissueless shell within two days (top left of the photo), unless predators prey on the weakened animals beforehand. The deadly pathogen is water-borne and can affect large areas in a very short time, it was said. The stability of coral reefs is under unprecedented threat, Bronstein said.

The disease is spreading along human transport routes, data from the Red Sea shows. It’s scary to watch thousands of sea urchins become skeletons on the seabed and disappear within a very short time, Bronstein says. So far, there is no way to help infected sea urchins.

Trigger changed environmental conditions?
Breeding populations of endangered species in reproductive systems separated from the sea is urgently needed so that healthy animals can later be released back into the wild. In addition, it is necessary to investigate which factors led to the outbreak. Changing environmental conditions are considered a possible reason.

Ciliates consist of only one cell and have hairs on their surface that allow them to move. They are commonly found in water and are usually harmless. However, relatives of the ciliates now found are already being held responsible for the mass deaths of other marine animals, such as sharks.

Source: Krone

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