The Trees of the Coral Jungle
The saying “can’t see the forest for the trees” refers to a person’s tendency to focus on the details to the point of missing the big picture.
Divers certainly have no problem seeing the big picture at Wakatobi. The clear, sun-dappled waters reveal a vast landscape of coral jungle. Sometimes, however, it is the details of the seemingly infinite collection of marine organisms – from fish life to the smallest of invertebrates – living within the corals and sponges that are easily overlooked. Some are well camouflaged, but many more are simply small, and lost amid the riotous colors and activity of the surrounding reefs.
In order to really grasp the depth of the forest we stop to marvel at the majestic beauty of an individual tree. Following this mindset, as we admire the underwater landscape, let’s slow down and focus on the trees—or in this case the trees of the coral jungle, sea fans.
If a tropical reef could be considered a coral jungle, the sea fans would definitely be the trees. Some sea fans grow as large as 4 meters in diameter, and while they are listed as coral, technically they are not true reef-building corals. True corals, sometimes called stony corals, produce a hard calcium-based skeleton as they grow. Sea fans, along with sea whips, are Gorgonians, a colonial cnidarian with individual tiny polyps that generate a flexible skeleton like the branches of a tree rather than a hard, stony base.
There are about 500 species of Gorgonians in the world’s oceans, most are found primarily in shallow waters. Of course shallow to a gorgonian is anywhere between 2 and 200 feet deep.
It’s hard not to get passionate about sea fans when there are so many in vibrant hues like some of the tall purple beauties found at Fan Garden, a site that truly lives up to its name.
While some Gorgonians contain symbiotic zooxanthellae algae (usually characterized by brownish colored polyps), which assist corals in getting nutrition via photosynthesis (the sun), those without zooxanthellae usually have more brightly colored polyps. Hence, sea fans of this nature ten to sport an array of vibrant color schemes – from purple, red, pink, and orange to rich yellows and gold.
Because they lack the additional nutritional source from the zooxanthellae, sea fans are more dependent on the nutrition they derive from filter feeding, making Gorgonians a more active predator than most other corals (yes sea fans eat other animals). While most hard corals primarily feed at night, Gorgonians are more active during changes in water flow, primarily when currents pick up.
The size, shape, and appearance of sea fans are highly correlated with their location. The more fan-shaped, flexible types of gorgonians tend to populate shallower areas with strong currents, while the taller, thinner, and stiffer branched relatives typically dwell in deeper, calmer waters.
Like some trees, sea fans are extremely slow growing and can take hundreds of years to reach a good size. And just like a big tree, a large sea fan is often home to a long list of animal life – from the more obvious like the numerous crinoids (seven to be exact) and sponges on this beautiful specimen at Lorenzo’s Delight, another popular site, to the tiniest of fish and invertebrates. Look hard and you can see the tiny pinkish coral hawkfish the diver has spotted perched on the edge of the sponge. And yes, sponges are animals too!
Living within the sea fan’s branches is a large variety of fish, including hawkfishes. One of the more notable and photogenic residents is the Longnose hawkfish. Typically two to four inches in length, they have a predominantly white body with pronounced red to orange striping, running both horizontally and vertically. As colorful as they are they can also be difficult to find as they are not very conspicuous against a sea fan of like color. The Longnose hawkfish likes to rest on the branches or in the midst of a sea fan typically seeking the high ground from where they can survey their surroundings. Perched from a good vantage point like a hawk on an outstretched tree branch, they can dart out to grab small crustaceans or other invertebrates, as well as fish swimming by. Sadly, one of their favored meals is the Pygmy seahorse, especially if one is highlighted by a diver’s camera strobe or hand held light.
Since we’re on the subject of the diminutive members of the Syngnathidae family, did you know that four of the seven species of pygmy seahorse are found at Wakatobi? And two of these are solely dependent on gorgonians, living their entire adult lives on a single sea fan; the Bargibant’s and the Denise’s (pictured at the top of the page), which looks like an extension of the brilliant orange network of the sea fan’s branches. Isn’t camouflage evolution wonderful?
With most pygmies reaching less than 1cm from head to toe, a sharp eye is required to witness this amazing spectacle. That’s when the assistance of Wakatobi’s eagle-eyed dive guides really pays off. Finding these little darlings of the sea fan can present a challenge. They are marvelously camouflaged – often having the same color and texture as the branches of their home. If pygmies feel threatened they are known to turn their backs to anything that approaches, making them even harder to distinguish from the fan’s tiny polyps. Patience and making slow and deliberate movements is always recommended for a positive view of this little celebrity.
While you’re looking for pygmy seahorses you just might encounter a close relative, the ornate ghost pipefish. Also small and highly colorful, the ornate, aka harlequin ghost pipefish, are regular sea fan dwellers and rank among the most exotic creatures in the Indo-Pacific. Their spike-shaped fin rays give them a jagged appearance like the arms of a crinoid. In addition to finding them hovering close to the crinoid’s arms, they will also make themselves indistinctive by drafting off the waving motion of a sea fan as it sways in the current.
One thing you can be sure of is that sea fans will grow with the broad side of their ‘fan’ oriented to prevailing currents. This maximizes their polyp’s ability to snare microorganisms from the water as it flows though the fan. For the host of small animals that take residence on the fan’s branches, this prime real estate makes food gathering easy without drawing attention. While not concerned about being inconspicuous, crinoids (a relative of starfish and sea cucumbers) will also capitalize on the sea fan’s strategic location, at the same time hosting numerous animals themselves.
The sea fan’s billowy branches also serve as effective sanctuaries for hosts of other sea creatures during the their juvenile development. Some of the most tantalizing finds for those with a keen eye are baby cuttlefish and squid that are no bigger than a grain of rice. Without using the sea fan’s protective forest of branches this little guy would more easily become somebody’s fast food lunch.
So, next time you are on the reef feeling the need to take in the forest, the big picture, simply explore a lone sea fan or two. Look closely, branch by branch, and see what wonders it may be harboring; you just may find you’ve grasped an even bigger picture of the coral jungle’s ecosystem.