24 April 2011

Signs of dugong at Chek Jawa?

We notice several furrows in Chek Jawa's seagrass meadows as we did TeamSeagrass monitoring early this morning.
Were these made by feeding dugongs on Chek Jawa?!

Here's another series of furrows. They were seen on the Southern tip of Chek Jawa. The same area where we thought we saw a dugong from the Jejawi Tower during an incoming tide last month. And also where we saw dugong feeding trails in 2007.
And yet another series of furrows. Dugong feeding trails are formed when dugongs chomp up seagrasses. Spoon seagrasses (Halophila ovalis) are among their favourites and these furrows were seen in meadows of Spoon seagrasses.
Dugong feeding trails are often the only signs we might have of dugong presence on Chek Jawa! How exciting! More about dugongs in Singapore and dugong sightings. Update: Dr John Yong commented on facebook "Ria, based on what I saw at Florida, these gaps look similar to the manatee feeding trails. Best to set-up remote, water-proof and underwater cameras, within these seagrass beds, to obtain direct evidence of dugong browsing."
While most of the seagrass meadows that I saw seemed lush and fine, I did come across areas with 'burnt' Fern seagrasses (Halophila spinulosa) and Spoon seagrasses (Halophila ovalis). Their leaf blades were blackened. I saw these burnt seagrasses on various parts of the shores including the area near the beacon, as well as near the Southern tip of Chek Jawa.
There were also large patches of bleaching Spoon seagrasses (Halophila ovalis). Bleaching results when seagrasses lose their chlorophyll. This happens when they are stressed. I'm not sure what is causing the stress to them.
Update: Dr John Yong commented on facebook "Burnt seagrasses - Chlorophyll fluroresence technique can be used to assess this situation. "Burnt" or photo-inhibition, as it is scientifically term, can be rapidly assess by measuring the Fv/Fm ratio, and some other established physiological parameters. For seagrasses, the "burning" may be due to unusually strong sunlight exposure during a low tide (coincidentally occurring at one time), higher water temperatures, and possibly rapid changes in nitrogen (and/or phosphorous ?) status of the marine water, in which these seagrasses grow. It is noteworthy that CJ "sits in" a nutrient rich-freshwater influx from S. Johor. So, I'm not sure whether the changes infreshwater-salinity may cause "osmotic adjustment" issue in these seagrasses (esp those already weaken by higher surface temp during low tides; plus etc factors), thereby making the chloroplasts in these cohorts of seagrasses to "die". When chloroplasts die, there is no green colour, and that particular seagrass is considered "burnt" (devoid of chloroplasts)." Thank you Dr Yong for this valuable insights and suggestions!

Today, there is also a public walk at Chek Jawa! As TeamSeagrass arrives to begin monitoring, the Ubin volunteers and staff were busy setting up for the walk.
How lovely to meet Joseph Lai (left) with Alan Tan. Joseph Lai is the man who first raised the existence of Chek Jawa before reclamation was deferred and it's great to see him back on Chek Jawa! Alan looks after the volunteers at Pulau Ubin and was one of the first to volunteer as a Chek Jawa guide before joining NParks some years later!
Among the special finds prepared for the public walk visitors is a tiny sea horse (Hippocampus kuda), a tripodfish (Family Triacanthidae). And also a fish that might be a Crocodile flathead goby (Psammogobius biocellatus). My photo of it didn't come out too well.
Another special find, a fish that appears to be a kind of Worm eel (Muraenichthys sp.).
While TeamSeagrass monitors the meadows, a few of us do a quick survey to see how Chek Jawa is doing in general. I intended to check out the Northern shore, but the tide was too high. However, a quick look at the marine life encrusting the legs of the boardwalk suggest that marine life in this area is doing well. There were lots of colourful sponges, ascidians, hydroids. Also snails and several cowries. I also had a glimpse of a mantis shrimp!
Today I saw many Haddon's carpet anemones (Stichodactyla haddoni). Only one of those that I saw was bleaching. The peacock anemones (Order Ceriantharia) I saw were all tucked up into their tubes on this hot day.
This looks like one of the Mud crabs (Scylla sp.) that we regularly see on our trips to Chek Jawa. I didn't dare get a closer look at it as they are quite fearsome. Here's my encounter with a gianormous Mud crab three months ago. I also saw some Flower crabs (Portunus pelagicus) large and small.
Chek Jawa usually has a great variety of echinoderms. Today, we did see a good sample of them. There were several Common sea stars (Archaster typicus) and lots of Sand stars (Astropecten sp.) on display for the public walk. Richard found a Biscuit sea star (Goniodiscaster scaber) on the way back from monitoring. We also saw many brittle stars.
Chay Hoon found this Garlic bread sea cucumber (Holothuria scabra). We also saw several Smooth sea cucumbers. And lots of sand dollars (Arachnoides placenta).
I came across three Mangrove horseshoe crabs (Carcinoscorpius rotundicauda) buried in the sand on this hot hot day. And Chay Hoon found a baby one on our way back. Seagrasses are an important habitat for horseshoe crabs and other marine animals to reproduce and grow up into adults.
Wow, a small sea pen (Scytalium sp.) with a tiny Painted porcelain crab (Porcellanella picta) that usually lives in sea pens.
Others who also surveyed the shore were Kok Sheng, who did a study of the recovery on Chek Jawa following mass deaths there, and Chay Hoon who also guides regularly at Chek Jawa.

On the way back to Singapore mainland, I notice the water in the wake of the boat was rather brown. The colour of tea. I noticed this too, around the time when there were mass fish deaths at Pasir Ris in Dec 2009. Oh dear.
Chek Jawa is close to my heart and I hope it will remain well. Regular surveys of our shores are important for a better understanding of them, and early indication of any impacts on them.

Other posts about this trip
  • TeamSeagrass blog
  • Ivan on facebook with sea cucumbers, crabs and other critters on Chek Jawa.
  • Kok Sheng on his blog and on the Chek Jawa project blog: sea stars and other echinoderms, carpet anemones and more. But four years after the mass deaths in 2007, things are still not quite the same as they were before.

2 comments:

  1. Fascinating! I do hope you will find and photograph a dugong!

    ReplyDelete
  2. Thank you for you kind good wishes! I do hope so too!

    ReplyDelete

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