As usual, the Knobbly Sea Star (Protoreaster nodosus) was the main highlight of every intertidal walk. There is a good population - more than 300 of them - on the island, coming in various colours.
We usually got the participants to take a group shot with the Knobbly Sea Stars.
Here's another group I guided on another date.
And this one was just taken earlier this morning!
The Sand-sifting Sea Star (Archaster typicus) is probably the most common sea star on Semakau, and possibly for Singapore as well. They can be found in huge numbers on many of our shores.
In recent years, we had been seeing more Cushion Stars (Culcita novaeguineae) on Semakau, especially juveniles. These sea stars apparently feed on corals, but interestingly we have been finding the really small juveniles among the seagrass. Wonder what they feed on when they were little...
The Rock Stars (Asterina coronata) on Semakau come in a wide variety of colours. So far I have seen pinkish ones, bright red ones, orange ones, black ones and brown ones.
Here's one of the greyish brown ones.
Several species of sea cucumbers can be found here, and we could usually see at least 3 or 4 species per trip. The above is a Stonefish Sea Cucumber (Actinopyga lecanora).
Many of the participants were amazed that huge sea anemones, such as the Giant Carpet Anemone (Stichodactyla gigantea), can be found in Singapore. These sea anemones have stinging tentacles to paralyse their prey.
However, some animals have adapted to the situation such that they can live among the stinging tentacles for protection, such as the Anemone Shrimp (Periclimenes brevicarpalis). This shrimp coats a layer of mucus around it which prevent the sea anemone from stinging it, and at the same time, gain protection from predators among the venomous tentacles.
Related to the sea anemones are hard corals, which are also stinging animals. The hard corals are able to build a hard skeleton from calcium carbonate for protection. Most of them, like the Faviid Coral (Family Faviidae) above, are colonial animals, and a colony like this can house thousands of little coral animals (polyps).
The soft corals, on the other hand, do not build a hard skeleton. Most of them can secrete chemicals to protect them from predators or prevent other animals from growing over them.
Often mistaken for corals, this pretty sponge (Neopetrosia sp.) is much simpler than the former. It is poisonous though.
The Funeral Nudibranch (Jorunna funebris), however, is not afraid of the poison, and feeds on the blue sponge. In fact, it is able to retain the chemicals from the sponge to make it distasteful to predators. Nudibranchs are sea slugs - somewhat like snails without shells.
We also have many snails (of course, with their shells) on Semakau. The above is a Pear-shaped Moon Snail (Polinices mammilla), which feeds on other snails and clams. It can secrete acid to soften the shell of its prey, create a hole, then feed on it while the prey is still in the shell.
A much bigger snail will be this Spider Conch (Lambis lambis), which got its name from the spines on its shell, which makes it resembles a spider (with lots of imagination).
The biggest shell we have on Semakau would be the Fluted Giant Clam (Tridacna squamosa), which can grow to about 40cm long!
It's interesting to note that the octopus belongs to the same group as the snails and clams - they are all molluscs. The former, however, has lost its shell. In fact, the only hard part of the octopus is its beak, and it can give a nasty bite with it.
Another interesting mollusc would be this Chiton. Instead of a one-part shell like the snails, or a two-part shell like the clams, or no shells like the octopus and slugs, it has an eight-part shell!
The flatworm is sometimes mistaken for a mollusc, but it is a lot flatter. The above is a a Pseudoceros sp.
There are many fishes too. This goby, Amblygobius stethophthalmus, was exceptionally cooperative and stayed still for us to take photos of it.
Several Blue-spotted Fantail Rays (Taeniura lymma) were spotted during the recent trips. These rays can give painful stings.
We were rather lucky to see a Tigertail Seahorse (Hippocampus comes) on one of the trips. It got its name from the stripes on its tail.
We saw Marine Spiders (Desis martensi) on several of our trips. These spiders hide in trapped pockets of air among cracks and crevices during high tide, and come out to hunt for small animals during low tide.
Semakau has many different species of crabs. The above is a Crenate Swimming Crab (Thalamita crenata). It's last pair of legs are flat and paddle-like, enabling it to swim. It is sometimes collected for food in the region by the locals.
The Mosaic Crab (Lophozozymus pictor), on the other hand, is said to be the most poisonous crab in Singapore. One single crab can kill 42,000 mice!
During the plant survey, we saw several of these crabs. I believed we have the ID some where...
My top find for the plant survey will be this young Xylocarpus rumphii, which is critically endangered in Singapore!
The locally critically endangered Grey Nicker (Caesalpinia bonduc) is both flowering and fruiting!
Interestingly, the Yellow Flame (Peltophorum pterocarpum), which is commonly planted on roadsides in Singapore, is also critically endangered in the wild here.
As a matter of fact, there are so many critically endangered plants and animals here on Semakau, that it would really be a shame if the authorities decide to reclaim more parts of the island.
Certainly hope that this island can be protected as a Marine Park some day.
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