It had been thought that clown-fishes were somehow immune to the anemone's stinging nematocysts. Close observations, however, have shown this not to be the case. The fish, through a series of brief—and careful— encounters with the actinian, picks up a substance in its mucous that the anemone recognizes as its own. The nematocysts don't fire when touched by the fish for the same reason one tentacle doesn't sting another.
Some cold-hearted experimenters tested this theory by scraping the mucous off a clown-fish and placing it back with its anemone. The hapless fish was immediately and unceremoniously stung.
Juvenile Clark's anemone-fish, in the distinctive bulb-tentacled anemone. 15 meters, Bunaken Island, Sulawesi.
Clownfishes are protandrous hermaphrodites; that is, all mature as males, and then a few sex-reverse to females. A typical anemone will contain a pair of clownfish, and perhaps a few young ones.
The largest fish in the group is the female. If she should die, the reigning male sex-reverses, and the dominant juvenile becomes the functional male. Juveniles sharing an anemone with an adult pair are hormonally stunted, and remain small.
Although clownfish are the only fishes to require an anemone host, other small damsels will opportunistically occupy anemones as juveniles, especially various species of Dascyllus.
Young Clark's anemonefish, Amphiprion clarkii, in the distinctive sand anemone, Heteractis aurora.
The spine-cheek anemone-fish, in the bulb-tentacled anemone. The spine-cheeked anemonefish varies from red to almost black.
A pair of Amphiprion ocellaris, in Haddon's anemone. This is not a known association in the wild.
Sea Anemones
Some of the giant reef anemones can reach a meter in diameter. All have zooxanthellae, and are thus found in relatively shallow water. They derive most of their nutrition from the algae, but also consume plankton and any other small animal unlucky enough to blunder into their tentacles.
Anemones can live to a ripe old age. In the 19th century, British naturalist John Dalyell kept a coldwater Actinia sp. anemone for 66 years. Over this period, it produced 750 young (by budding), 150 of these after the age of 50. The anemone eventually outlived the scientist.
Some 10 species of Indonesian anemones, in three families, host clownfish. The systematics of this group was in some confusion until Dr. Daphne Fautin reorganized it in 1981.
Cryptodendrum adhaesivum. Lies flat; very short tentacles. Hosts only Clark's anemonefish.
Entacmaea quadricolor. The bubble anemone. (See photo at left.) Hosts 11 species.
Macrodactyla doreensis. Very long, widely spaced tentacles. Usually dull color, buries column in sand. Hosts 2 species.
Heteractis aurora. Dull color, buries column in sand. Distinctive tentacle shape (see top photo above.) Hosts 7 species.
H. crispa. Long, thin, almost pointed tentacles that often seem tangled. Hosts 11 species.
H. magnifica. Brightly colored column, blunt tentacles. Often photographed. (See small photo opposite.) Hosts 10 species.
H. malu. Buries column in sand, fairly short tentacles, limited range. Hosts only Clark's.
Stichodactyla haddoni. Haddon's carpet anemone. Short-tentacles. Grey, with white radial stripes. Hosts 6 species.
S. gigantea. Bludru anemone. Longer tentacles, larger than Haddon's. Hosts 6 species.
S. mertensii. Merten's anemone. Colorful; largest carpet anemone, to lm across. (See bottom photo above.) Hosts 10 species.
— David Pickell
One of the piscivorous cone shells (Conus sp.) devouring a small goby. Most cone shells eat worms, but the relatively few fish-eating species are very dangerous.
The octopus has highly developed eyes and a very sophisticated nervous system. It is thus considered "intelligent," and people find it hard to believe that it is a mollusc. The white color of this specimen suggests exhaustion, and perhaps the photographer was a bit overzealous in getting this shot.
Trochus. Top shells (Trochus spp.) are relatively large (6-8 cm.), and conical. Before the advent of plastics they were widely collected for the manufacture of buttons. Removing the grubby outer layer of shell reveals the lustrous nacre, or mother-of-pearl beneath. Until the invention of Bakelite, and the many plastics that followed, shell nacre for buttons was an important business in Indonesia. Today they are still collected, most to be used in souvenirs and to supply the small market for "real" buttons.
Clams and Oysters
The bivalves include such familiar forms as clams, oysters, mussels and scallops. All have two articulated shell halves that can be closed with a large muscle. It is this muscle that makes bivalves so prized as seafood. With a very few exceptions, bivalves cannot move, like gastropods, and thus most have adapted to filter-feeding. They draw water in through one tube or "siphon" and pass it out through another. This stream of water passes through the animal's gills, which serve the dual purpose of respiration and filtering out food particles.
All bivalves must hold their shell halves at least slightly ajar to maintain water circulation through their bodies. But when danger threatens they are clamped shut. Some Indonesian bivalves gain further protection by boring into corals and reef rock, so that predators cannot reach them. The boring is achieved by a combination of chemical action and rasping with the two shell haves. Eventually, reef bivalves become so encrusted with sponges, coralline algae, bryozoans and cnidarians that they are barely visible.
Giant clams. The giant reef clams, Tridacna spp., have a different means of feeding. Like reef-building corals, Tridacna clams harbor zooxanthellae in their fleshy mantles, and can thus "manufacture" most—or perhaps all—of their own food. Like corals, they require lots of light, and tend to be found in the shallows. They grow with the hinge of their shells down, and their rippled gape facing the sun.
There are seven species of Tridacna, of which the giant clam, T. gigas, is the most dramatic. These animals can reach a meter and a half in diameter. An animal that big could be a century old. Although smaller than T gigas, T squamosa has a beautiful ruffled shell. The fleshy mantles of Tridacna clams are beautiful, varying in color from brown to yellow to green to blue, with contrasting spots or mottling.
Tridacna clams are a great delicacy in Asia, particularly in Taiwan, and their shells are made into terrazzo in factories in Surabaya. Over-harvesting has greatly reduced their numbers throughout Indonesia. Shallow reefs in Eastern Indonesia that used to support literally fields of giant clams have been stripped in just the past few years. There is fear that the population in many areas is no longer at a self-sustaining level.
Recently, however, researchers at the Micronesian Mariculture Demonstration Center in Palau, headed by Gerald Heslinga, have discovered a method of "farming" giant clams by inoculating the veliger larvae with zooxanthellae. Once the symbiotic algae is in place, the clams need only a good supply of sea-water and plenty of light to thrive. The farming operation requires little room, and the clams reach 10 centimeters across in just two years. Because of the commercial potential for these clams, a number of pilot farms have recently been established in the Pacific region.