Going soft

Food fight: fairy basslets and Dendronepthya soft coral vie for planktonic food carried by strong currents past Fiji’s rainbowed reefs All photos: Douglas David Seifert Family trees: Dendronepthya soft coral... Gorgonian sea fans... And sea whips... are all members of the Alcyonaria family that do not lay down calcium carbonate skeletons On the up: soft corals utilise spicules to form a temporary skeleton created through hydrostatic pressure in their tissues Crowded house: coral reefs are the most diverse ecosytems on Earth; Sinularia soft corals and anthias thrive in Fiji’s waters

When the talk turns towards coral reefs, generally speaking, the corals that come to mind are the reef-builders: the hard or stony corals of the order Scleractinia. These corals are well known not so much because of what they are like when living but rather because of what they leave behind when they die – a calciferous carbonite (limestone) skeleton built upon generations of earlier skeletons, with differing species forming a variety of shapes reminiscent of terrestrial life: tabletops, the brain, animal horns, mushrooms, lettuce, pillars and so on.

Corals are in fact colonies made up of thousands of tiny individual – but genetically identical – invertebrate animals known as polyps. The polyps are essentially miniature versions of the familiar sea anemone design: a tubular, sac-like body cavity with a central single opening (which serves as mouth as well as anus) surrounded by tentacles with a base attached to the substrate. A unifying living tissue called the coenenchyme, which allows food to be transferred throughout the colony, interconnects each individual polyp.

In the Indo-Pacific, there are 23 families of soft corals with 90 genera, and 18 families with 89 genera of hard corals; in the Atlantic, the hard corals significantly outnumber the soft. The greatest number of coral species is found in the Pacific Ocean and possibly the best all-around concentration of both hard and soft corals is to be found in Fijian waters (certainly, the Fijian dive operators and tourism board think so, proclaiming Fiji ‘the soft coral capital of the world’ in their marketing campaigns). Fiji boasts 200 species of coral of both persuasions; the Great Barrier Reef has some 450-plus, but more hard corals than soft.

According to the examples from a study of the theory of island biogeography, remote oceanic islands generally have fewer species and more endemics than islands not separated by an effective water barrier of thousands of miles of ocean (and separated by millions upon millions of gallons of sea water). French Polynesia has no soft coral, none, yet, interestingly enough, Fiji has a super abundance. Why? A theory currently being debated is that the Fiji Islands sit atop the Fijian Plate, which was once part of the Coral Triangle (present-day Indonesia, Malaysia, the Philippines, Palau, Papua New Guinea and the Solomon Islands) and, following the mechanism of plate tectonics, broke away as the sea floor underwent transformation. Over time – say, seven to 12 million years – the Fiji Islands rode the Fijian Plate like a skateboard across the back of the Pacific Plate, bringing many of the endemic tropical species (including multiple species of soft coral) to their present position and the relative isolation of Fiji’s contemporary location. Fiji is now a separate ecosystem with surviving species remnants from its original location, but has also had sufficient time for its own distinctive species to develop. This new theory is a subject of heated debate, but for whatever reason, Fiji does have soft coral in many varieties and colours.

My cover was to come to Fiji to celebrate my friend Stan Waterman’s (the legendary underwater film producer and photographer) 85th birthday with a diving cruise on board the liveaboard Nai’a, but my secret agenda was to see if Fiji’s reputation for abundant and colourful coral was deserved or just a lot of hyperbole. I am cynical by nature – although I suppose I could have simply taken Stan’s word for it – still, there was serious investigating to do and I would investigate seriously. The other passengers on the trip were unaware of my plan. We had all dived together before in various places and although everyone was more experienced than I – well, at least older and members of the order of diving dinosaurs – I can bluff with the best of them.

But from the moment I entered the cool, clear, blue waters off Fiji’s northwest coast and the bubbles cleared from my entry, there was no question that Fiji’s coral reputation was well founded. A current was carrying me towards the reef at alarming speed. The reef rose from the depths to 5m and was as wide as a rugby field. Its sheer walls were studded with the branching arms of all manner of gorgonians, sea whips, sea fans, and wire corals. Fleshy, tumescent Dendronepthya soft corals coloured in shocking pinks, vivid yellows, flamboyant purples and bold scarlets swayed in the current and vied for reef space with the, by contrast, subdued-looking but healthy hard corals and sponges.

Schools of anthias swirled and danced among the underwater forest plucking plankton from the water and darting here and there to evade predators: lionfish, grouper, snapper and others. Gaudily coloured wrasse flitted past meandering pairs of butterflyfish. Silvery jacks rocketed in from the midwater to ambush small fish caught out from coralline sanctuaries. The reef was so alive that the senses were overwhelmed: all manner of fish and invertebrate life going about their business in a flurry of activity defying comprehension. Absolute beauty in nature; a true illustration of the oft-used word biodiversity, but at its most magnificent and entrancing.

All corals are part of the phylum Cnidaria (from the Greek word cnidos, meaning stinging nettle), a classification of more than 9,000 aquatic species that includes jellyfish and whose members are all distinguished by having nematocyst stingers. Modern corals evolved nearly 200 million years ago, though they have been in existence for 450 million years and have survived many mass extinctions. Corals are further categorised in the class Anthozoa, which is made up of nine orders and contains some 6,000 species in three subclasses: the Ceriantipatharia (tube anemones, black corals and wire corals); the Zoantharia or Hexacorallia (hard corals, mushroom anemones/corallimorphs and sea anemones); and the Alcyonaria or Octocorallia (blue corals, sea pens, sea fans and soft corals).

Hexacorallians and octocorallians (including sea fans – according to coral scientists, there is no distinct dividing line between soft corals and gorgonians) share the same environment but have evolved separately and developed distinctly different strategies to exploit different niches. Hexacorallian polyps have six tentacles (or multiples of six, hence the name; a few have no tentacles at all), and lay down a calcareous carbonite cup encasing the polyp called a calyx, into which it can retract for protection. Octocorallian polyps, on the other hand, have eight tentacles and no discernible hard skeleton; instead, they have minute, spiny, needle-like particles (spicules) made of calcium carbonite called sclerites embedded in their tissue. These give their tissues support, as they use hydrostatic pressure – pumping water into their mesogleal tissues and maintaining it – to achieve a rigid scaffold-like framework or hydroskeleton to give them a massive structure when necessary for feeding. When not feeding, the water pressure is reduced, causing the soft coral to shrink. Sclerites also give the soft coral a thorny texture to deter would-be predators and are essential in identifying soft coral varieties, for it is only at the microscopic level that many of the species can be differentiated. Gorgonians (sea fans and sea whips) lay down a fibrous, horny organic material called gorgonin, upon which the individual polyps are sited, as well as the stalk framework that forms a living net above the reef.

All corals are nocturnal plankton predators – anyone who has ever seen a reef at night when all the polyps are out feeding understands the truth of the phrase ‘wall of mouths’ – but daytime feeding is a different matter. Hard corals remain in relatively shallow, warmer water that is comparatively deficient in nutrients. To augment their nutritional requirements, hard corals have evolved into living greenhouses for tiny one-celled plants called zooxanthellae, which they cultivate in a symbiotic relationship. The zooxanthellae are given protection from predators and in return, as the tiny plants convert sunlight energy and carbon dioxide into chemical energy, the coral polyp is fed a diet rich in carbohydrates and fats, and the waste returns to fertilise the zooxanthellae in the forms of nitrogen, phosphorus and carbon dioxide.

The zooxanthellae also give coral polyps their pigments and colours, as is evidenced by the very real threat of extended elevated sea temperatures and coral bleaching – where the zooxanthellae die off, leaving only a white or translucent polyp behind, itself on a slow path to demise unless water temperatures return to within the zooxanthellae’s tolerance. This partnership enables the hard coral to lay down a permanent limestone skeleton, to grow, and to reproduce at a rate greater than erosion or acidification can inhibit the coral’s growth. This partnership accounts for 90 per cent of the hard coral’s nutrition and is the reason why large coral structures can grow to extraordinary size and flourish over generations.

Octocorallia, for the most part, do not rely on zooxanthellae for their nutritional needs. While they do contain zooxanthellae in their tissues, they are generally inefficient at photosynthesis and rely on the chance capture of passing plankton. Unlike stony corals, most soft corals thrive in deeper, nutrient-rich waters with less light intensity where there is a substantial current flow or upwelling. If they are situated on a steep slope with a strong current and the passing food is abundant and not a matter of chance, soft corals can reach massive sizes: up to 2m for some species such as Dendronepthya, or larger in sea fans such as Subergorgia, which can reach 3m in height and 4m in width!

Octocorallians go with the flow – or more precisely, against it. For the suspension-feeding soft corals seeking planktonic prey, the current acts as natural Viagra. As the current builds in intensity, the individual polyps in the colony pump sea water until their cells are taut. At full extension, the soft coral takes on the characteristics of a terrestrial bush or tree: a stalk elongates, the branches and lobes stretch out into the current, and the structure is rigid with hydrostatic pressure and every polyp on the soft coral colony is out and feeding. With the loss of the current flow and the diminished food occurrence, the pressure is released and the tree branch deflates until the time to feed is at hand again. In a matter of minutes, the soft coral can go from flaccid to erect or the inverse as is required by feeding or for defence.

Octocorallians secrete a mucus containing a stew of various chemical compounds called secondary metabolites, which perform a multitude of functions to ensure the colony’s survival. The metabolites act as an anti-fouling mantle to protect the coral from algae invasion and microbacterial infection; they contain an amino acid that functions as a natural sunscreen for protection against ultraviolet radiation; and they include chemical deterrents toxic to would-be predators and an allelopathic substance, such as found in some plant species, to inhibit the growth and spread of neighbouring corals and other encrusting organisms in the fierce competition for reef real estate. Despite the presence of these repellent secondary metabolites, some soft corals and gorgonian species play host to a number of cryptic creatures in an apparent but undescribed symbiosis with the coral: the soft crab (Hoplophrys oatesii) is often found in Dendronepthya sp.; allied cowries on gorgonians and soft corals; the pygmy seahorses (Hippocampus bargibanti and Hippocampus denise) on specific sea fan species; and various nudibranchs are associated with soft corals and gorgonians.

Although different species of coral can exist in near temperate waters or at great depth, for the most part, hexacorallians only thrive in a narrow range of conditions: they must have warm water – a stable 21– 29°C temperature is preferable – which narrows its worldwide distribution between 30° north and 30° south of the equator (although there are exceptions); abundant sunlight; clear, pure sea water unpolluted by sediment or diluted by freshwater outflows; a relatively shallow habitat from just below the surface to 18–27m deep; and protection from violent crashing waves and pounding surf. Octocorallians are more tolerant of colder waters if those waters bring them an increased food supply, which is why soft corals can often be found in deep water and in caves.

The current pulled me along and propelled me past the face of the reef. There was nowhere to hang on: every centimetre of the reef was alive. I swam downward to where I imagined the current would be lessened. More species of colourful soft corals – Chironepthya, Muricella, Siphonogorgia – were attached to the undersides of ledges. Their branching arms projected out into the current as if waving to me as I helplessly passed by. The current flow lessened as I reached the backside of the reef. In the lee where the current abated, so, too, the reef changed dramatically. The lurid hued Dendronepthya shrivelled from its engorged cauliflower structure to a pile of fleshy, prickly knobs attached to the rock. No current, no parade. Eventually I would surface, then count the hours until I could dive back in to this vividly coloured, phantasmagoric living dream of a coral reef. Fiji’s reefs really do have the soft coral variety that makes every dive a sublime experience.

Douglas dived Fiji’s rainbowed reefs with Stan Waterman, courtesy of Rob Barrel and Cat Holloway, while on board the Nai’a liveaboard. Phone (+679) 345 0382, email This e-mail address is being protected from spambots. You need JavaScript enabled to view it or visit http://www.naia.com.fj