The Duke group had the privilege of visiting Chek Jawa with RIA TAN, CHUA EE KIAM, RON, ALVIN, NPARKS, and the Sea Grass Volunteers. We were overwhelmed by the generosity, sensitivity and kindness of our Singaporean hosts. Thanks up front to Ria, NPARKS, RON and Dr. CHUA. We will not rest until we find a way to return the favors.
My specific mission was three fold, 1) get my group to take pictures that document the journey to complement a parallel experience to our temperate estuarine mud flat; 2) look closely at the flat and use the animals that are still there to support the hypothesis that the mass die off observed about a month ago was due mainly to the huge influx of fresh water from the rains; 3) make a prediction about the ecological future of Chek Jawa.
Singapore is ever changing. The new boardwalk that is being installed will enable many many more people to visit and appreciate Check Jawa . The new volunteer hub building is equally impressive.
The easiest animals to assess at Chek Jawa are the sessile or virtually sessile signature animals. All these animals are sensitive to low salinity beause they conform to the environment around them —carpet anemones, peacock anemones, sea cucumbers, and button shells. These have all been more than decimated. I saw two (20 cm diameter) small very healthy carpet anemones, several dozen Peacock anemones, two sea cucumbers and no button shells. Hopeful signs, the peaock anemones were clearly healthy and there were three new 3 cm carpet anemones.
The only echinoderm that appeared unimpacted was the cake sand dollars which were numerous and of all sizes. Perhaps being buried in the sand, enabled them to survive.
Crabs are the next easiest animals to assess because they are highly visible. Crabs are capable of with standing low salinity because they can regulate their ion balance. The fiddler crabs, bubbler crabs, and hermit crabs appeared unaffected. Most the flower crabs even the immature females were heavily parasitized. In my part of the world, crab parasites have their own salinity optimum . That may be true here also. The level of parasites was higher than in my previous 5 years of visits.
The burrowing snails also tolerate low salinity by burying in high salinity sediments. The presence of egg collars of moon snails everywhere, indicates that these snails are doing fine.
Animals that live in the sediment are harder to assess without digging them up. Two things told me the sediment dwellers are fine: 1) plenty of holes and worm tubes with growing ends; 2) Evidence of extensive sting ray feeding activity. If the sediment dwellers were gone the rays, which use electroreception and chemoreception to find their living prey, would feed elsewhere.
Every thing I saw support the idea that low salinity from fresh water killed the sensitive Chek Jawa animals. Will Chek Jawa return to it previous state? Only time will tell. However, intertidal sand flats are dynamic, a classic disturbed environment. Most of Chek Jawa has not changed. I’m betting the flat will return to its previous spectacular glory and relatively quickly. With luck I will be able to visit again next year with my Singaporean friends and be privileged to help report the return of the sessile signature species.