A fulsome bloom of sargassum, aided by evening monsoons of wintry discontent, threatens to wrack what little opportunity remains this year to plunge into the flats that surround Singapore's southern islands. The sunken rims of Pulau Semakau, St John's Island and Pulau Hantu throb with thalli that sprout from benthic holdfasts to smother the reefs with unruly layers and vie with the corals for the power of the sun, which runs out early in the day during this season of swift, sullen clouds. The algae, which erupt with no regard for the polyps, sponges and bivalves that share their bed and similarly survive on scattered rays, are governed by rhythms of murky provenance; nutrient spikes or heatwaves may fuel their spread, but whatever the trigger, the macrophytes surge and sink with a frequency that defies prediction, withering at the end of each cycle to stew on rubble or embark on secret trysts from apparent sterility.
While they grow, the lamellae provide the substratum for minute communities that scour the weed for edible filaments. Lurking in the dense clumps for prey and protection are coin-sized filefish, wary scorpionfish, prowling octopuses, paddling crabs and caridean shrimps with no hint of colour save in their eyes and freshly stuffed bellies. Colonies of hydroids may also set foot on the sargassum, the better to snare passing zooplankton with their stinging arms; in turn, they draw the appetites of at least one nudibranch which mows the cnidarians with toothy jaws and conceals its own presence via dorsal parapodia that mimic the tips of tattered blades. There was, alas, no sign of these dendronotids at St John's Island last Friday, despite the oppression of a thick brown belt that cloaked the reef edge and left little room for trod. The only opistobranch to emerge from the fronds was a hairy sea hare that gave itself away when its mantle flaps separated to unleash a siphonal gasp. More commonly seen on northern shores subject to estuarine inundations and cyanobacterial blooms, Bursatella leachii is a creature of low estimation with a body of branching papillae and bright blue ocelli that usually escape notice when the slug flops on muddy bottoms or forages on dull seats. Small individuals, perhaps the issue of larvae who were too eager to settle down, show up at times in the south, but these grazers never reach the lengths of animals from softer flats and fail to swamp these shores before their food runs out and the survivors march to close the gap between life and breath.
A somewhat less ephemeral aplysiid inhabits vegetation of firmer mien. Finding Phyllaplysia is nonetheless still an exercise that strains the eyes and taxes the limbs, for this slug's abode, Enhalus acoroides, seldom occurs in sprawling meadows by smaller islands. Each outpost of tapegrass must therefore be scrutinised, its legion of hermit crabs disregarded and dismissed, and aberrations on the leaf surfaces discounted only when doubly inspected. And there is always the constant threat of distraction from more charismatic beasts that beckon from the peripheries of torched vision.
Pale longitudinal striations and a slim, compressed body help to mask these sea hares on the narrow confines of their habitat, reducing molluscan forms to indiscernible pads that meld with the veins of a vascular plant. Two dark spots near the base of the rhinophores probably do little more than offer a stereoscopic sensation of light and allow the animal to maintain its desired plane of existence on a world of few dimensions. The fibres of Enhalus are almost certainly too tough for the slug, but the straps, especially older foliage, usually attract an ample population of microalgae and other fouling organisms. For Phyllaplysia, the rights to this bounty and its disposal in good taste are fair trade for the privilege of living unseen and unchecked on a platform that's always green but never truly clean.