19 August 2009

The Great Walls of the East Coast

T'was a Long March that started at ungodly hours. But the team thought we should spend the last of these super low tides to check out East Coast Park.
Often dismissed as dead reclaimed shores, we were quite impressed by the teeming marine life found on the seawalls there.

Every hard surface that is submerged in water for some time seems to eventually become thick with marine life. Oysters cram into every suitable spot, forming a crinkled zone full of crevices. Which are happily taken up by more mobile creatures such as limpets, onch slugs (Family Onchididae) and Purple climber crabs (Metopograpsus sp.).
While the flat walls were teeming with tiny unidentified crabs, there were bigger Sally-lightfoot crabs (Grapsus albolineatus) hiding in larger crevices among rocks of the seawalls.
Some walls had large Purple climber crabs that seemed unafraid of people. This one seemed to say "I don't like to eat duck for breakfast, please go away".
Other busy crustaceans included the Sea slaters (Ligia sp.). Often called sea cockroaches, sea slaters are NOT insects. If you ask me, sea slaters (photo on the left) look nothing like cockroaches (photo on the right). And there WERE cockroaches on the high shore, probably attracted by food litter left behind by park users.
One wall was teeming with tiny shore crickets! These ARE insects, and sometimes found on the shores at low tide. But I've not seen so many before in one location.
Another insect seen in large numbers was this strange little unidentified moth. Marcus says he's also seen this before at Chek Jawa. Read more about them on his blog entry about this trip. They don't seem to be eating anything on the wall, but many are seen applying their backsides to the lush carpet of tiny seaweeds on the walls. Are they laying eggs? The rest also saw spiders on the wall!
There were of course lots of marine life on the walls. Many are tiny and icky. Such as flatworms (Order Polycladida), ribbonworms (Phylum Nemertea) and other bristleworms. Others are larger and sturdier such as snails: mostly Drills (Family Muricidae), Nerites (Family Neritidae) but also some Spiral melongenas (Pugilina cochlidium). James has lots of lovely photos of these animals on his blog post.
My favourite hard surface snail are the periwinkles (Family Littorinidae), especially the tiny Knobbly periwinkles (Nodilittorina trochoides). These tough little snails can outlast and outcompete bigger snails and thus rule the higher and drier parts of the walls.
In some parts where there are rocks and small stones on the low shore, these are coated with a bewildering variety of marine life: on the left possibly an orange colonial ascidian, on the right a blue sponge?
These encrustations go berserk on the underside of a rock, where it is wetter, cooler and safer.
Here, the surface is coated in sponges, ascidians and other blobby and slimy lifeforms. They are all animals as the sun don't get down there. As well as tiny snails, limpets, keelworms and porcelain crabs.
Here's another look at a patch of life under a rock.
In crevices under a rock are less compressed animals such as these solitary ascidians (the white blobs) and a small banded bead anemone. After looking under a stone, we are careful to put the stone back exactly the way we found it. So that the animals are not squashed.
The porcelain crab (Family Porcellanidae) is very flat and almost looks like a two-dimensional cartoon of a crab. It is quite at home under a rock and we saw lots of them today.
In pools among the rocks were also many little banded hermit crabs in tiny shells. Marcus saw one large Striped hermit crab (Clibanarius sp.). Skipping about the wave-splashed rocks were mudskippers. Such as this small one which might be the Dusky-gilled mudskipper (Periophthalmus novemradiatus).
This frisky one playing the waves is a Gold-spotted mudskipper (Periophthalmodon chrysospilos).
Some unexpected encounters included this odd snail-like animal with a shell and a large foot which James found on the wall. It sure looks like a bubble snail (Family Haminoeidae). But I've only seen this kind of snails on silty sandy shores and so far have not encountered them on seawalls!
Another surprise, a tiny patch of what looks like living Pore hard coral (Porites sp.) encrusting a small stone.
And high and dry, wedged inside a dead oyster shell, was a fish! It was very much alive! I have no idea what kind of fish it is.
The seawalls jut out at regular intervals between vast stretches of sandy shores. The shore, however, was steeply sloping so there was very little alive encountered here. Besides very many skittish Horn-eyed ghost crabs (Ocypode ceratophthalmus) that would disappear into the waves when we came close.

But I did take a closer look at the remains of dead plants and animals washed up on the shore. Which is difficult to do in the daytime as the sweepers would have already removed most of this. There were lots of shells of bivalves of various kinds.
There were also bits and pieces of intriguing seagrasses! In one small area, I gathered bits of Tape seagrass (Enhalus acoroides), Needle seagrass (Halodule sp.), Sickle seagrass (Thalassia hemprichii), possibly Serrated ribbon seagrass (Cymodocea serrulata) and even Noodle seagrass (Syringodium isoetifolium)!
There were also many propagules of mangrove trees washed ashore. Including the very long propagules of Rhizophora mucronata, medium length propagules of other Rhizophora species, and squarish propagules of what might be Ceriops sp. Given a chance, mangroves can recolonise our shores!
Unfortunately, many of the natural flotsam is usually efficiently removed together with the litter that washes up on the shores by the armies of sweepers that work the Park.
Also, there were two stretches of shores where works were being done. It seems to involve redoing the seawalls as well as putting down little rocks on the shore and adding more sand. This of course, wipes out marine life there.
A disturbing sight far from freshwater inflows was a dead frog.
Is it the victim of an animal release? It is not unknown for freshwater animals to be mistakenly released into the sea and visa versa.

While the East Coast area was not as rich as we expected it to be, marine life is quite thick in places left alone. Once the works on the shores settle down, perhaps some of the more spectacular animals such as sea fans will return. We should continue to visit the shore to see how things go.

By the end of the low tide, we had walked a very long long distance! Indeed a Long March to check out the Great Walls. Sleep deprivation results in lame corny comments.

Other posts about this trip


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