Expedition 2023 South Seas

Perfect hard corals but hardly any soft corals

The stony coral formations were quite sensational! There were fields of Acropora table corals at a depth of 30 metres, stretching over 150 m and extending from the steep edge at 20 m down to a depth of 40 m. What was interesting was not only the size of the field, but the fact that there were NO other corals between them! The only organisms that had made it between the corals were black sponges.

These black sponges also appeared in large numbers at another location: Exactly where reef damage was visible on the outer reef, presumably caused by storms. The sponges appear to have an ecological advantage due to their lack of species or coral growth.

Although the species richness of the stony corals was large, we had seen more elsewhere. It was more the quantity of the corals and their intactness that impressed us. There was no sign of climate-induced coral bleaching anywhere (!). Whenever we spotted any white coral fragments, we usually found the culprits not far away.

The culprits were always the crown-of-thorns starfish (Acanthaster planci), whose feeding marks caused the white colour on the coral. At night, even more crown-of-thorns came out of their hiding places and went on their raids. However, we were unable to confirm it was a crown-of-thorns plague, as known from other oceans.

This may be because we also sighted some of their natural predators, such as the Triton's trumpets.

The largest soft corals were leather corals, which were found in a few places like patches in the stony coral reef. But then only ever ONE species had spread there. In addition to leather corals, we also sighted fields of coral anemones and some occasional black wire corals. The reason for this could be that there is simply not enough plankton, which many soft coral species feed on. Only those species that can also feed on light are to be found there.

Fiji, Bligh-Water (Vatu-i-Ra)

We never saw any Nephthea soft corals, not even on steep slopes with strong currents, where they are often sighted in Fiji (Bligh passage/Vatu-I-Ra), and other places. But then Fiji is 4400 kilometres away.

Anemones and their inhabitants were also a rarity! Even though there weren’t many anemones, we identified three species. Amphiprion chrysopterus usually inhabited the anemones. But we also found Dascyllus trimaculatus there.

At the oceanic threshold of the northern passage of Fakarava we photographed an anemone at a depth of 40 m (!). At this depth, anemones are normally no longer to be found, as the zooxanthellae (algae) living in their tissue are dependent on sunlight. But the clear water, which allows the sun's rays to penetrate to great depths, made it possible.

Expedition South Seas

JBL Expedition South Seas I and II

Perfect hard corals but hardly any soft corals

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Expedition South Seas

JBL Expedition South Seas I and II

Perfect hard corals but hardly any soft corals

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