25 January 2012

Lush reefs of Sisters Island with surprise crab

What a pretty crab! I've not seen one like this before! And Kok Sheng found a basket star too!
A small team surveyed Sisters Island yesterday. It was relief to see that the reefs seemed fine.

The crab had pretty blue markings on the underside!
Here's a closer look at the the crab. It  has dark eyes with white spots, and its pincer tips are crossed like scissors. There are blue spots near the mouth and on the pincers too. It looks like some kind of Swimming crab (Family Portunidae).
How wonderful to see this beautiful basket star (Family Euryalidae) which Kok Sheng found. We rarely see this animal on our shores. This is only the second time we've seen one on Sisters Island since Chay Hoon found a basket star here in 2007.
A closer look at the basket star. It has a tiny star-shaped thing on the upper side (upper left photo). The mouth in on the underside (upper right photo). I also noticed conical transparent things on the ends of the small curly branching arms. I have no idea what they are. The animal was producing a lot of slime!
Even though I'm half blind, I managed to see this Tiger-tail seahorse (Hippocampus comes)! It was quite lively and hard to shoot.
The only nudibranch I saw was this Phyllidiella pustulosa which is commonly seen on many of our reefs. Chay Hoon found two Bornella sp.
My main concern was to see how the corals are doing here since our last trip in Oct 2011. Although there is still a massive bloom of Sargassum seaweed (Sargassum sp.) on Sisters Island, the water is clear and the tide surprisingly lower than predicted. So we could carefully survey the island to see how the corals there are doing.
The first thing I noticed was lots of white spots on the rocks near the edge of the reef. These were pink coralline algae that had turned white. Coralline algae acts somewhat like a pink cement, encrusting dead corals on a reef. Oh dear. Is this something to worry about?
A closer look at the 'rocks' and it seems most of them are actually dead corals encrusted with coralline algae. Lots of long Sargassum seaweed are attached to the 'rocks'. Did the seaweed lift up the 'rocks'? Is that how so many 'rocks' build up on the reef flat?
It was good to see that many of the large hard corals were nice and brown and unbleached. Hurray!
Sisters Island has among some of the best reefs that are easily accessed by the public. With a wide variety of hard corals, including many that are not commonly seen.
The huge colony of Brain anchor coral (Euphyllia ancora) is still there. Although the centre portion of the colony is dead, the edges seem very much alive.
Here's a closer look at the U-shaped tips on the tentacles that distinguish this family of corals.
I also came across three small colonies of Acropora corals (Acropora sp.).
There were several medium to large Brain corals (Family Mussidae).
There were small clusters of Branching montipora corals (Montipora sp.).
I saw many colonies of the pretty Carnation coral (Pectinia sp.). This coral seems to be doing very well on Sisters Island. The coral has a delicate fluted skeleton which is hidden under the fleshy tissues.
I also saw several Ridged plate corals (Merulina sp.), which also seems to do well here.
I came across a small half-dead colony of Lettuce coral (Pavona sp.).
The gatherings of Circular mushroom corals (Family Fungiidae) are still there and they all look happy and unbleached. These corals grow unattached to a hard surface!
I also came across a small Bracket mushroom coral (Family Fungiidae) which grows attached to a hard surface.
The more common coral species were also abundant. There were many colonies of Favid corals (Family Faviidae) of all sizes. I saw several Tiny-ringed corals (Cyphastrea sp.). The colony with bumps looks unusual.
There were many Pore corals (Porites sp.) of all sizes. Most of them seemed healthy although I saw a few that were rather pale.
I saw a few small Flowery disk corals (Turbinaria sp.) and all of them were rather pale. There was also one nice delicate looking Thin disk coral (Turbinaria sp.).
I saw a few Crinkled sandpaper coral (Psammocora sp.), and one colony of Galaxy coral (Galaxea sp.). There were some small Anemone corals (Goniopora sp.) colonies, but I didn't manage to get to the big colony in the middle of the lagoon due to the Sargassum bloom. I also didn't see any Cauliflower corals (Pocillopora sp.).
I also saw a variety of healthy, small colonies of Leathery soft corals (Family Alcyoniidae).
I came across an enormous cluster of these Ridged corallimorphs which I don't often encounter.
The more commonly seen Carpet corallimorphs were also seen here and there.
I came across this large sea anemone wedged among the rocks. I'm not sure what it is. Could be the Bubble tip anemone (Entacmea quadricolor) as a few of the tentacles had a white band. Later on, we also saw one large Haddon's carpet anemone (Stichodactyla haddoni) on the sandy shore.
We left soon after sunset so we didn't see too many fishes. And we were very relieved NOT to find any driftnets on the island, unlike on our last trip here in Oct 2011.

Sisters Island lies next to major international shipping lanes in the Singapore Straits. Accidents can result in oil spills, such as the oil spill earlier this month near Pulau Senang and Pulau Pawai. Some container ships like this one, pass alarmingly close to Sisters Island. 
There was even a container ship that crashed into and got stuck on a rock near the Sisters Islands in 2009. Here's a photo of this ship in the distance, between the two Sisters Islands.
The two Sisters Islands are in the foreground with the ship in between the two islands.
There are indeed many things that can harm the reefs on the Sisters Islands. Thankfully, so far, they seem alright.

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