The sandwiched child of a trio of small patch reefs due west of Pulau Hantu and the smokestacks of Bukom, Terumbu Pempang Tengah is separated from its landward sibling by a channel rife with wrecks. The reef sits atop a crest of rubble that gives way to a broken basin of soft and stony corals along the northern fringe, while the eastern slope is relatively sparse and pierced through the knee by a tongue of sand. Low, branched colonies of Montipora form a grey plain near the centre of the flat, which is otherwise dotted by puddles of crabs and isolated outcrops.
The coralline rock, over which polyps once grew, now serves as a foothold for more primitive animals: sponges in the guise of thick chalices, awkward branches, hispid globes and layers of porous tissue that encrust the surface with a solid splash of primary colours. Within these glass chambers and siliceous channels dwell brittle stars, sea cucumbers and snapping shrimp that sip and sup from streams of water powered by inner walls of flagella, organelles in a state of perpetual flux and whose bearers offer a glimpse at how free-swimming cells might have traded their independence for collective benefits. Modern poriferans continue to thrive in marine and a few freshwater habitats, and hold their own in a fitness landscape of more advanced metazoans. Few predators, too, have the stomach for spicules, save sea turtles and pomacanthids. A good number of dorid nudibranchs also specialise on sponges, using extra-oral secretions to dissolve their prey in-situ into a proteinous soup, which is imbibed along with defensive metabolites that line the spawn and skin of the slugs. It probably pays as well to declare the presence of noxious goods before a fatal bite and nudibranchs such as Glossodoris atromarginata refuse to be wallflowers, creeping over the reef with folds that leave little to the imagination and gills in a whorl of their own.
The bloated coenosarcs of soft corals, resembling ruffled omelettes, lobed discs or leathery folds, pepper parts of the flat that receive ample servings of planktonic currents. Stranded colonies collapsed into untidy flaps or limp digits, but some portions, trapped in shallow water, still throbbed with a profusion of autozooids, minute polyps with eight pinnate tentacles and the wisp of a column, that hide the firm but flexible matrix under a bed of feeding bodies. Also present, but in smaller numbers, were nephtheids in the shape of weedy shrubs lined with pale-stemmed florets, by which hovered tiny filefish in similar shades but nervous garb.
Growing alongside the octocorallians are the true reef builders, the scleractinians who capture fluid ions to carve shells of aragonite that rise over time as each polyp lays down fresh ridges to create room for itself, buds off to form a new branch or simply expands to occupy a greater share of the seafloor. Beneath this living veneer of tentacles and inflatable tissue is a base of columns and dividing walls that support the colonies as they grow in girth, height and complexity. The reef, for all its rigid layers and tiny towers, is a trove of ecological niches whose inhabitants survive by mastering its rhythms and making alliances that maintain a balance of power between those who feed among the corals and those who feed on them.
The hub of the flat is a field of porous boulders and branching corals in the genus Montipora; the latter, with their grey stems and bare tips, resemble a garden of brittle lichen kept low by the dry mow of spring tides. In slightly deeper parts, the plate-like base of another acroporid supports an unruly array of stout branches that terminate in broad, blunt fingers traced by vein-like ridges, between which sprout masses of tiny, brown polyps. Meandering ridges also characterise Pachyseris rugosa, but the corallites of this species are part of the superstructure, with finely toothed columellae that serve as partitions between lines of barely discernible polyps. Dull green with white trimmings, the colonies are somewhat plastic in expression but here, they grow as thick forts that assault the surrounding rubble with new walls of territory.
Turbinaria may also form plates that creep over the substrate, but the typical members of this genus build raised discs with often ruffled edges, which in some colonies develop into arborescent complexes with broad tiers and overlapping canopies. The largish polyps are widely spaced and emerge from a common anchorage, which cloaks the corallites and envelops the colony in a skin of gaudy colours. These assemblies of warm browns, blues and greens stand in contrast with the pinks and purples of Goniopora, whose exuberant polyps stretch out from a submassive skeleton to swirl with the tide and swing to the waves. The hemispherical colonies appear impossibly dense and individual columns probably undergo some degree of deflation before they can retract into their shelters. A few, however, produce modest polyps from boulder-like or encrusting colonies that recall their poritid cousins.
A motley assortment of other hard corals shatter the contours of the reef with angular bulges and irregular masses. Some colonies are little more than a dozen strong and face an uphill struggle to outpace their neighbours and engulf the surrounding rock. Others have gained purchase on favourable spots and use this headstart to nurse a convex battery of soldiers who launch sting operations on nearby settlers. But for all its belligerence, Galaxea remains a brittle star on a stage where armoured mounds, clad in dense cones, stiff honeycombs or a maze of solid brain waves, have the upper hand in withstanding the depredations of polyp-phagous animals and the battering of tropical storms.
There are also corals that refuse attachment in adulthood, severing ties with their juvenile stalks to rest on the seabed in apparently random aggregations. It's not entirely clear if the individuals get around on their own accord or ride convenient surges, but fungids are certainly able to shake off the threat of burial under loose sand and avoid the pains of coralline scrums. The compact, parasol-like species seem to prefer siltier lagoons, but Terumbu Pempang Tengah, located as it is by the slipstream of a dire straits, is dominated by elongated fungids that bristle with septal rays and fleshy bits.
Structurally similar to scleractinians but lacking hard parts, corallimorphs inhabit somewhat sheltered nooks of the reef, where they may obscure the rubble with a layer of coelenterate rugs. Each cluster usually consists of individuals of varying size, the likely result of fissile offshoots from a lone pioneer. Conventional wisdom suggests that the order subsists on the byproducts of inhouse zooxanthellae, but the animals, which are known to snare fish and sweep their borders for would-be trespassers, probably harbour a reservoir of survivalist tricks within their broad oral discs, which house sparse, or non-existent, rings of stubby tentacles.
We try our best to sidestep these biotic elements of the reef flat as we scour the scene for tridacnids and other tantalising members of the intertidal community, for these ephemeral playgrounds, little touched and hardly trampled, are wont to attract creatures that shy away from the fringes of walled islands and have long skirted mainland shores. Patches of sand between the growing outcrops pose a modicum of risk, but the stingrays that invade the shallows to root out shellfish seldom allow themselves to be cornered and maintain a wide berth from clumsy waders.
The main victims, as it were, of rubbery treads were zoanthids, whose seemingly discrete polyps are joined at the foot by invisible mats that permeate unconsolidated sediments. From these stolons rise short columns topped by tentacular rings of green or brown, which double over when disturbed to become limp blobs of coenosarc. This cnidarian horde, overlooked on account of its near ubiquity and tendency to overrun every tract of exposed silt, endures and probably shrugs off the subconscious brunt of visitors who favour the more fragile architects of the reef and plot against time and tide to restore, or at least record, a fraction of the life aquatic that once coursed these waters and fed the forefathers of this maritime city.