The annotated budak

Reef of rolling stones

We first noticed these little crabs about a year ago during surveys of the Cyrene Reefs that began, as the season dictated, a couple of hours before day broke and the dredges of the port authorities became evident in the waters between these patch reefs and the container ports of Pasir Panjang. There is a gap in the rubble near the northern rim of Terumbu Pandan, where a tongue of sand breaks the lime barrier and invades the meadow at the heart of the flat. Here, the inflatable finds a gentle slope and intertidal explorers enjoy a soft launchpad to begin their wanderings across the shore.

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Protoreaster nodosus prowl the edge of the seagrass meadow in rude droves and unrestrained colours. Some are hunched over pieces of rubble, with their extruded innards making short work of encrusted organisms. Others sprawl on the grass, exchanging invisible messages with their mates or awaiting the signal to emit cells of mutual, meotic attraction. As the sky brightens, unfortunate individuals that fail to languish in deeper pools greet the sun with deflated crowns and cringing arms as the source of their strength and rigidity seeps out of their grooves. On the sandier stretches of the flat are slightly less imposing echinoderms: purplish sand dollars, spiny Archaster in pre-coital assemblies, sea urchins with a sartorial bent, and cucumbers with hides in the shapes of stones and snakes. Amid these familiar bodies, we find at times a few rarities – cakes, cushions and oreasterids distinguished by cones on their marginal plates and a striking network of spines and tubercles on their aboral discs. Here, too, are carpet anemones with sticky tentacles and smaller creatures within their folds, as well as free-wheeling polyps with fair names and foul rubs.

As expected during visits on tropical springs, the waters of Cyrene last Tuesday were ruffled by a chill wind and brooding clouds that rushed in from the southwest to battle the eastern light. The storm line just missed the reef, though, and unleashed its wrath instead in a shroud of grey that turned the city invisible but spared the crew who arrived to collect specimens for the southern leg of the Comprehensive Marine Biodiversity Survey of Singapore. Among those who sampled the flat were Len McKenzie of Seagrass-Watch, who was trying to determine why tape seagrasses at Cyrene were suffering severe foliar damage compared to other nearby Enhalus beds, and Gretchen Lambert, a veteran taxonomist specialising in ascidians, dense colonies of which dot parts of the meadow. 

The crabs in question betrayed their presence in the rockish strand a little to the left of the landing site, where patches of fine sand and grass intermingle with substrates of coarser material. Slightly more substantial outcrops provided refuge to the odd Eriphia ferox, which must lack for cover and companionship in these isolated ridges far from richer fields of rubble, while tiny broken-back shrimp in glassy shades of green and brown paddle in futile loops around shallow pools until they tire and fade from sight on a strap of turtlegrass. These crustaceans easily command attention for their disarming charm and delicate meanderings, but it became hard to ignore a regular series of lurches that took place in the same torch beam and which could not be handily explained by a rogue wavelet. The movement came from clods of rubble that wobbled or jerked with no visible source of animation. Turned over, each piece of coral rock gave up its true identity as the extended phenotype of a small brown crab with strongly built chelipeds.

Not a few groups of higher crustaceans have evolved the habit of using bits and pieces of their environment, whether inorganic, dead or still living things, as additional layers of armour, the better perhaps to stay ahead in an arms race between those that hide and those that bite, harder. Hermit crabs are arguably the most well-adapted of these decapods, having developed twisted, vermiform abdomens that fit the coils of dead gastropods as well as primary chelae that effectively plug the apertures; these mobile retreats may even have an offensive element in sea anemones that settle on or are transplanted by the crab onto the shell. In the deep sea, where empty shells are scarce, this relationship has become obligate; one genus of actiniarians secretes a chitinous roof over its parapagurid vehicle, which obtains protection in return for transporting its stinging rider to fresh pastures.

Among the true crabs, dromiids are the best-known backpackers. These rotund animals snip and don befitting fragments of sponges or colonial tunicates, which are held by modified legs and continue to grow over the carapace of their bearer. Sea anemones are the preferred armament of Lybia, which wields the polyps like boxing gloves on its claws, and Hepatus box crabs, which carry the cnidarians on their carapace. Certain spider crabs sport hydroids or corallimorphs on their limbs and flanks, while larger majids such as Camposcia retusa turn their entire bodies into a motley array of sponges, polyps, seaweed, bryozoans and other sessile taxa. Another group of brachyurans, the dorippids or porter crabs, enjoys modest fame for their use of dead leaves or other debris as lightweight cloaks; larger members of the family unabashedly press into service hapless creatures such as fire urchins, sea anemones, biscuits stars and even nudibranchs.  

The little crabs that use chunks of rubble as roving shelters are in quite a different class altogether. For one, the animal must conduct the business of foraging for food and mates while lifting a rock many times its bulk and weight. The crab grips its home using its final pair of legs and gets about by pushing against the seabed with its robust chelipeds. The hollow occupied by the carapace is also peculiar; each concavity has a wall with distinct impressions, the likely result of sustained rasping by the crab's chelipeds, which have rough, beaded granules on the outer surface. Beyond this sculptured aperture is a passage that leads to a deeper chamber, in which the crab nestles when the rubble is disturbed. When the coast is clear, the crab creeps out of the rock towards the substrate and using deft legwork and leverage from stout claws, flips the slab back over its body in a fast and fluid stroke that recalls the spinning of a top.

Identified as Actumnus setifer by Peter Ng, this crab has long been regarded as an excavator of burrows in live and dead coral, sponges and soft stones. Two closely related species have been observed to carry living pieces of branching and massive corals, in which snug retreats are fashioned and which, when overturned, the crabs assiduously manœuvre to reposition the primary opening downwards. Similar behaviour was reported for A. setifer in 2008 by Australian authors who described how these pilumnids dwell in a "moveable coral shelter" consisting of a downward-facing entrance and feeding chamber, a habitation chamber and various other smaller openings which may aid in respiration and food detection. The crabs seldom, and only swiftly, leave their refuge, except to grab food and perhaps to mate. The conjecture of earlier observers that the arrangement is mutually beneficial is disputed, however, as there is little to suggest that the corals gain in mass and survival from being dragged across the reef or rubbed bare by rough claws.

Local specimens inhabit colonies that are already dead or have perished after persistent bumping against other rocks, and the observed habitat at Cyrene, with its mosaic of fine sediments and sheltered outcrops, appears similar to that of crabs in Moreton Bay. How this mode of carriage emerged, and whether it is exhibited by discrete populations within the species' range or only when conditions permit it, is still unclear.  The gap between creating fixed galleries and gallivanting on unobstructed flats is perhaps one that is forded by crabs beholden to a calculus that juggles the availability of environmental resources, the cost of a heavy burden and the risks of life in the holes of exposed reefs.

Snaked trysts

Two banded file snakes were fucking on the flat off the northern rim of Pulau Semakau, where the perimeter bund of a bulging landfill meets a wall of artificially planted mangroves, one evening when their union was interrupted by a gaggle of explorers who stalked and stumbled over the shore, torch in hand and hopes in thrall to a day of late tidings. The male, who kept his coils in a tight spiral around the nether regions of his mate, was a clean-living fellow, though his stripes were rough on the edges and had little of the sheen of a recently moulted individual. The lady, to her credit, was a tramp who had allowed her hide to hang loose and become a habitat for green filaments.

A snake at sea but confined, it seems, to the zone below the pools of bockadams and before the reefs of true sea serpents, Acrochordus granulatus may venture, and even thrive, in freshwater reservoirs via tidal gates or estuarine channels. Locally, they may be encountered on the fringes of untamed islets such as Pulau Sekudu or the skirted slopes and seagrass beds of Pulau Semakau, where their glum and sluggish disposition belie an ability to intercept, constrict and swallow good-sized gobioids and goatfish, which let their guard down before the jaws of a reptile whose low metabolic rate allows it to remain submerged and still for long periods. As with other squamates, the males wield paired hemipenes that are extruded from a cloaca at the base of a surprisingly short tail. With his lower torso suitably entwined around the female, the male everts one of his hemiphines, which latches onto the inner walls of his mate to facilitate prolonged coitus while the unused hemi-organ swings freely. This physical bond probably accounted for the reluctance of the pair to break loose and cut short their consummation, even though they failed to consult each other on which direction to take in sidestepping the spotlight.  

Keen eyes are not an asset for file snakes, which hunt in murky pools and plunge their heads into dim lairs in search of demersal prey. Yellow-lipped sea kraits, on the other hand, swim in clear waters, using their paddle-like tails to propel themselve through seaweed and benthic growth as they pursue eels and other fish. For all the power of their bite, these elapids are vulnerable to predators such as sea eagles, sharks and even swimming crabs – their eyes are hence attuned to detecting motion, be it by food or foe and, as if to make up for an anatomical chink in their armour, their tails have evolved photoreceptors, prototypic eyes as it were, that tell the animal, during attempts at taking cover, if its rear end remains in sight and at risk of flightful talons. Snakes at sea, it seems, still slither with secrets that suffer not the soft stabs of intertidal missions at shining a harsh, hollow light at beasts we love to hate and never hope to know.

High power

Squirrels are more often heard than seen. Bird-like calls of 'chewit-chewit' pierce the understorey of forests in which saplings and lianas grow at a density that allows slender squirrels to leap between vine and branch without setting foot on the ground. Their larger cousins, Callosciurus notatus, are no less chatty, punctuating their foraging with shrill chirps and violent swipes of a proud, plush tail. The rodents, for all their justifiable wariness of primates that have ditched the high ground of a treesome life, can be remarkably tolerant of humans when they are busy stripping bark off trees, rooting in the foliage for fruit and insects, or engaged in death-defying pursuits of rivals or mates that involve ridiculous dashes, unmeasured leaps and blinding tumbles through secondary growth and mangrove corridors, accompanied by shrill oaths delivered with staccato fury.

Squirrels don't usually sit and stare, but when they do, few casual visitors to local parks and reserves suffer from the intrusion of arboreal mammals into their line of foresight or endure the disruption of small, warm bodies to their constitutional subroutines. But there was no escaping the high power of a pair of liquid globes a mere head above eye level by a trail through swampy backwaters overrun by sun skinks and skimming dragonflies. The animal's compact size and lack of an obvious streak on each flank suggested Sundasciurus tenuis, but the bushy tail and heavy build demurred. It took a few moments of misplaced focus for a second, rather larger, squirrel to become evident, perched on a limb that had been sawn off and cauterised to prevent the forest from attacking civilised intruders. Caught flat-footed perhaps as they scrounged by the path, the pair had taken flight in subterfuge, the subadult mimicking its parent or heeding a call to halt. It was, possibly, a nod to caution by the older beast on behalf of an offspring that is yet to earn its stripes and has not mastered the art of flinging its buff and brown frame through the undercanopy without missing a step or making a monkey out of a tribe that has never fallen to the level of naked apes.

Chained reactions

Only golfers and other idle souls have the wherewithal to spend the latter half of a cloudy day on the green by MacRitchie Reservoir, where men in loud orange vests labour by the banks to remove bog moss before returning to base in a municipal bathtub of a boat. A skimpy path runs between the singular holes and a shallow basin that supports an alien menagerie: cichlids from Africa, Central and South America, Malayan cyprinids, North American terrapins and freshwater clams that run riot in artificial lakes, though few venture into the streams that have survived a century of unsustainable croppings. Parts of this track, which skirts with visible menace the terrain of a distant club, are bisected by a low wall of fountain grass, an ornamental herb with invasive potential but whose habitus offers a refuge for orbweavers, which occupy nearly every gap between the stalks and many other, smaller, planes of existence in a hedge of brown and purple blades.

The dominant spider on this well-brushed fringe appears to be Argiope catenulata, one of five local members of a genus that spins vertical traps, to which they add the finishing touch of dense zigzags made from aciniform silk, a tough, non-sticky fibre also used to wrap eggcases and struggling insects. This species, which has been recorded from swampy fields in open country, is distinguished by a broad, oval opistosoma marked by an irregular, tapering, dorsal stripe that overlays three bands of variable colour –  a chained or catenulate combination said to meld with the silvery patterns of the animal's snare. In habit, though not in choice of habitat, Argiope catenulata deviates little from its kin, which variously occupy mangroves, scrubland and forest margins. The females, which hang head down on hubs marred by unruly gusts, blundering dragonflies or difficult prey, respond to disturbance by arching their bodies and, if pressed, shaking the web with arresting vigour, using their bulky abdomens as counterweights for a rhythm that may help to throw off the senses of wasps and warblers. Harassed further, the spider may slip to the other side of the web or drop into the undergrowth, where she will sit out the disruption to her routine before pulling herself back up to face a parlour of tiny mates and return the blow of pressures that refuse to let up on this shore of exposed and endangered waters.

A berried passion

Keppel Island, which serves as a handy launchpad to the southern reefs, is now linked to the mainland by a sleek plank, on which privileged drivers and perplexed cabbies coast toward a club of fine dining and fancy yachts. The restaurants overlook a small marina where some degree of fouling is tolerated, as least on the pontoons and seawalls which suffer the stain of corals, gorgonians and sea anemones, and thus lure a scoundrous horde of fish that run rings around the boats and refuse to pay for their board. Behind the establishment runs a jogging track, by which manicured shrubbery obscures the native vegetation of an islet that provided refuge to green pigeons and guarded the passage through the dragon's gate into the docks of what used to be called New Harbour.

The island's former name, which invited confusion with namesakes further to the southwest, is admirably haunting, however. One account of its origin tells of an encounter between a domiciled fisherman and a decapod he had snared, a brachyuran of colossal proportions with whom he struck up a dubious acquaintance. This friendship came with strange benefits, including nocturnal companionship and, presumably, intimate strokes by the creature's maxillipeds and shell-shocked aftermaths. The crustacean was strangely non-plussed by its bedmate's marital status, an oversight that led to its downfall in the hands of a jealous wife, who reduced her rival to dismembered portions and invited her kin to a seafood feast. Thanks to unsanitary food handling or/and the dying curse of a crabby end, the villagers couldn't quite swallow their meal and soon died in loco motion. Upon returning to find his lover half-digested and his relatives well-disposed of, the fisherman was said to have mourned his leggy catch more than his legal spouse, and in the ways of nameless myths, "news of the crab's death spread rapidly across the ocean bed and piscatorial demolition parties were organised" to assail the island and render it unfit for habitation. The moral of the lesson, it seems, is that a prized catch can lead to a ménage with possessive spirits and wild affairs with no exit clawses.

Daylight robbery

For about a century, the phosphate mines of Christmas Island welcomed labourers from China and Southeast Asia, in particular Malaya and Singapore, who journeyed to this craggy isle, a solitary rock on the eastern reaches of the Indian Ocean, to dig, ship and die for the profits of colonial overlords. Aiding them in their, often final, tour of duty were chandlers such as Ong Sam Leong – Baba man about town, amateur mariner and tycoon extraordinaire – who rounded up recent, mostly Cantonese-speaking, migrants, ferried them to this coralline outpost and granted them all the rights of indentured men, coolies bound to the service of mining concessionaires and marked by a tattoo on their hand, who worked 74 hours a week to repay the debt of their passage and survived on little more than rice, salted fish and a dash of vegetables, for which they were charged a princely sum. Armed foremen caned laggarts, beri-beri culled the lame and those who had cash to spare sank into opiate dreams or plunged themselves into the flesh of painted ladies at a house of distant repute.

The settlement grew rather more complacent after the Second World War, though life on the island retained much of the social stratification of more glorious eras. Workers from Malaya and Singapore continued to drain the island's natural reserves, earning for their efforts the discrimination of second-hand employers and later, a battle of Conradian proportions that turned the colonists into citizens of a luckier state. There were, presumably, lots of coming and going, by steamer or flying boat, between the mines and Singapore in those decades, and it's possible that some of these commutes included the occasional free rider, oceanic wanderers that had reined in their pleopodal segments and would have never reached these parts on their own. Some probably perished in backyard kitchens, while a few may have eluded their handlers to roam local coasts until they ambled within sight of curious crowds, to which they almost certainly responded with backward lunges and the threat of stabby feet.

Widely dispersed in the Indo-West Pacific, Birgus latro is absent from the South China Sea, a biogeographical trait that may stem from a zoeal aversion to near-shore flavours or exist as a relict of once unhindered currents. Native fans of terrestrial decapods, who might fancy stumbling upon a beast in blue in ill-maintained coconut groves, must therefore content themselves with the rustlings of Coenobita, good-sized but markedly smaller anomurans that prowl unswept beaches and steal little more than the coils of dead snails. Young robber crabs also strap on – with the likely aid of their strongly chelate fourth pereiopods – empty shells, broken husks or film canisters, but as they grow, their naked abdomens deposit chitin to withstand danger and dessication, while layers of fat accumulate under the telson, the reserves of a diet of rich fruit, carrion and organic scraps. On Christmas Island, in the absence of now-extinct native rats, Birgus rule the slopes as the dominant non-bipedal predator, though this counts for little against the wheels of vehicles driven by dutiful visitors, which now squash a thousand or more crabs each year. In this age of climatic change and economic miracles, even the toughest of robbers must cede privilege to the laws of asylum, which offer a far more humane, though perhaps no less hopeless, end to desperate souls than that rendered to dispensable minions by long-dead barons and their heirs, now asleep and awaiting their fate in tombs on a hill.