Zoanthids of Kusu Island

4am and we're at Kusu! This time with Dr James Reimer, a zoanthid expert who is with the very cool sounding JAMSTEC (Japan Agency for Marine-Earth Science and Technology).Dr James is a great person to be with out in the field. Although he just arrived in Singapore a few hours before, he was bright and cheery and delighted us with all kinds of insights about our zoanthids.

What are zoanthids?

Zoanthids look like tiny sea anemones with tiny tentacles on a tiny oral disk supported by a tiny body column. But while sea anemones are solitary polyps, most zoanthids live in colonies like corals do. But zoanthids don't produce a hard skeleton like the hard coral colonies. Instead, their skin is leathery.

Each polyp has a smooth, flat oral disc with short tentacles, usually in two rows close to one another. When they are out of water, the tentacles are tucked into the body column so that the zoanthid may look like sausages or blobs. Dr James says he prefers to see them with their tentacles expanded to have a better idea of what they are.Zoanthids may have three different living arrangements. Each zoanthid polyp may be solitary but located near one another. These polyps are large with thick, fleshy polyps on tall columns. Or the zoanthid polyps are joined one another in the colony by stolons (tube-like structures that spread across the ground like a root or runner).

On one part of Kusu Island, the shores are thick with zoanthids. We are glad that Dr James finds this area interesting. They are mostly two diffent kinds of zoanthids.These small ones are Zoanthus species also sometimes called Button zoanthids. They can come in many different colours and patterns. Dr James says these generally don't incorporate sand in their bodies so they are smooth to the touch. He also said that although in the past, they were assigned different species by their shape, DNA studies show that many are actually the same species. The most commonly seen species on Kusu Island were Z. sansibaricus.
The bigger brown ones are Palythoa species (although previously called Protopalythoa, Dr James says DNA studies show that they are Palythoa). And most of them on Kusu's shores were Palythoa mutuki. Dr James says some of these incorporate sand into their bodies so they are more rough to the touch.

In some zoanthid species, the polyps may be embedded in a common, shared mat of tissue. The tissue may be strengthened by incorporating sand. The colony may form mats on the sand or encrust rocky areas. Like these Palythoa tuberculosa, which I call the Rubbermat zoanthid...haha.Here you can see some of the polyps open in the portions that are submerged.Dr James is quite intrigued to find many of these Palythoa tuberculosa on Kusu Island with 'fractures'. Each clump is actually a colony which might be clones of one another.Here is a comparison of the various kinds of zoanthids, with a 'fractured' Palythoa tuberculosa.

The shape of the same zoanthid species may vary depending on where they are found. Those inhabiting areas with strong waves tend to be short and hug the surface. Others found in deeper, calmer waters are taller, with longer tentacles. One the advantages of being a blob is to be able to take on different shapes.

Dr James found these other species of zoanthids quite interesting.He will have to study them more closely to determine exactly what they are.Some zoanthids contain powerful toxins to protect themselves against predators. The most toxic marine poison, palytoxine, was discovered in a zoanthid. Minute quantities of palytoxine can paralyse and even kill.

So we are careful not to handle zoanthids with open wounds on our hands or touch our mouth or eyes after handling them. However, some animals have adapted to the poison and even eat zoanthids. These include the Hairy crab (Pilumnus sp.). Dr James says he has seen them eating zoanthids.

Most of zoanthids feed on plankton, some also feed on finer particles. Many harbour zooxanthellae (symbiotic algae) inside their bodies. These carry out photosynthesis and may contribute nutrients to the host polyp. Dr James shared that his studies show the same species of zoanthids may have different kinds of zooxanthallae. But zoanthids also capture and eat food from the water. Dr James said some zoanthids he kept for study ate salmon!

We saw this poor Palythoa tuberculosa that was sick.The white portion is spongey and soft and rotting. Dr James says zoanthids can also bleach just like corals as they lose their zooxanthallae. As such, they are a good indicator species as they tend to be more sensitive and bleach before the hard corals do. However, bleaching in zoanthids is not as obvious as in corals. The only way to be sure is to monitor a bunch of zoanthids to observe changes in their colour.

Some photos and ids shared by Dr James can be seen on the CoralPedia website

Along the way, we also spotted many other creatures on this rich but narrow reef at Kusu Island.

For some reason, there were lots of cowries out and about this morning.I saw this Wandering cowrie (Cypraea errones) which I usually encounter more often on our Northern shores.
We saw two of these beautiful Onyx cowries (Cypraea onyx). This cowrie is listed among the threatened animals of Singapore due to habitat loss and over-collection and is rarely seen.And we also saw an Arabian cowrie (Cypraea arabica)! This large cowrie is rarely encountered and is also listed among the threatened animals of Singapore due to habitat loss and over-collection.

Dr James shared that in Japan, there are some times of the year when the villagers go out and collect cowries as they appear in numbers. Wow, could there be some Cowrie Event this morning that we still don't know about?

Another interesting snail is the Spider conch (Lambis lambis) which are still commonly seen on our reefs, although it is also listed among the threatened animals of Singapore.This one had an orange design on the inside of the shell. The animal is using its long muscular foot tipped with a knife-like operculum to turn itself back the right way.I also saw this lovely flatworm (Pseudobiceros fulgor) which I have not seen for many years.
And Chay Hoon spotted this well camouflaged Spotted-tail frogfish (Lophiocharon trisignatus)! Although it was quite large, it blends in perfectly with its surroundings and thus requires an eagle eye like Chay Hoon's to spot.

We also saw octopus, clown anemone fish and of course lots of hard corals and soft corals and the other amazing marine life on this little island.

All too soon, it was sunrise and the tide came in.Here's Dr James in green shirt having a last look at the zoanthids on Kusu Island before we break off for breakfast.

Looking forward to our trip tomorrow, in a few hours, to check out the zoanthids on Pulau Hantu!

(This entry is really late because yesterday, my desktop died. Then my backup laptop actually caught fire -- well it was smoking! Normality resumed just two hours ago. And only made possible thanks to Victor Ang, my PC Angel, who delivered a replacement laptop within 24 hours. Thank you Victor!)