Diving Indonesia Periplus Adventure Guid. David Pickell
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Название: Diving Indonesia Periplus Adventure Guid
Автор: David Pickell
Издательство: Ingram
Жанр: Биология
Серия: Periplus Adventure Guides
isbn: 9781462909155
isbn:
— David Pickell
MARINE LIFE
The Varied Inhabitants of Indonesia's Reefs
The waters surrounding the islands of Indonesia form the richest marine habitat on earth. Indonesia lies at the epicenter of species diversity for the entire tropical Indo-Pacific region, which stretches from Madagascar and the Comoros islands in the west to the easternmost of the Pacific islands—a vast 12,000-mile sweep through the Indian and Pacific Oceans.
Perhaps 3,000 species of fish, and several hundred species of coral populate the reefs off the larger Indonesian islands. A 19th century Dutch ichthyologist cataloged 780 species of marine fish just in Ambon Bay alone, almost as many as can be found in all the rivers, lakes and seas of Europe. (Alas, this reef has been destroyed, dredged after World War II to provide building materials for booming Ambon town). Even the healthiest Caribbean reef has just 10-20 percent of the species diversity of a comparable Indonesian reef.
The islands that now make up Indonesia are likely to have been the genetic "source" of Indo-Pacific marine life. This region has remained tropical for 100 million years, exposed to the strong sunlight that makes tropical waters so much richer than temperate waters, giving the animals a long time to diversify.
Although ocean currents distribute fish widely, the further across the Pacific one goes from Indonesia, the fewer species will be found. For example, 123 species of damselfish are found in Indonesia.* (see note at right.) In the Philippines, 118. In Papua New Guinea, 100. In Fiji, 60. In the Society Islands, 30. In the Galapagos, just 18. The entire Caribbean holds just 16 species.
One million years ago the Ice Ages began, periodically tying up much of the earth's water in ice. This lowered sea levels by as much as 130 meters, reducing the tropical Atlantic to a small refuge in the south Caribbean, decimating the animal population. The Indo-Pacific never suffered such an extinction.
But volcanism and continental drift caused similar disruptions in Indonesia, and it is probably because the islands provide such a wide variety of habitats— deep sea trenches, rocky shores, sand and mud flats, sea grass beds, mangrove swamps and, of course, coral reefs—that the fauna here is so diverse.
While muddy turtle grass beds, mangrove swamps and estuarial waters are of immense interest to the biologist, divers usually find little in these shallow, turbid waters to hold their attention. When divers talk about tropical water diving, they mean coral reefs.
A long-nosed hawkfish, Oxycirrhites typus, sitting among the lacy antipatharians encrusting a wreck, just off Molas beach near Manado, Sulawesi.
A Compendium of Reef Life
There are so many species present on the Indonesian reefs that even specialists can not give an exact tally of their numbers here. With this in mind, the aim of this chapter is to provide an introduction to the major groups of animals that will be seen when diving on Indonesian reefs. No attempt at comprehensive coverage is made.
Algae
Although people often mistakenly think of many of the reef animals—corals, gorgonians, sea "anemones"—as plants, what is perhaps most striking about the coral reef is the apparent lack of plant life. Other rich coastal marine environments, for example the kelp forests off California or the sea-grass beds and man-grove swamps off some of the Indonesian islands, are obviously based on the photosynthetic production of oxygen and nutrient-fixing by algae or higher plants.
Turtle grass, Thalassia sp., is one of the very few true marine plants. Although not found on reefs, back-reef areas may have beds of turtle grass, which nourish crustaceans and juvenile fishes as well as the dugong.
The marine algas Udotea (top) and Halimeda can both be occasionally found on the reef. Udotea is only lightly calicified, but the calcium carbonate disks of Halimeda are in some areas a major component of the reef substrate.
On the reef, however, despite its teeming life, plants seem absent. In fact, plants are the primary producers on the reef, just like every other environment. Most of the algae found on the reef grows as a short "turf," a fine carpet of hairs that is a mix of dozens or hundreds of species of brown, red and green algaes. While diving, look closely at an area of bare coral rock and you will probably see a fine carpet of "hairs" growing on it.
The algal turf grows at a prodigious rate, but a herd of grazers—tangs, parrotfish, damselfish, sea urchins, snails and many others—keeps it clipped short. If an area of reef were caged off to prevent the entry of herbivores, the turf would quickly sprout into a thicket. The farmerfish damsel (Stegastes lividus) does just this, by force of personality keeping out all intruders from his own luxurious green patch of hair algae.
Some reef algaes, the so-called coralline algaes, are calcified, providing them with protection both from grazers and physical damage by surge. These appear as small pink "trees," or flat, encrusting pink or lavender growths on old chunks of coral. Some of the coralline algaes grow in areas of very high wave action, indeed preferring areas that are too turbulent for even corals to survive.
On reefs facing the open ocean, it is a ridge of coralline red algae that receives the full force of the crashing ocean waves, dissipates their energy, and allows less robust organisms including corals to thrive. Other varieties of coralline algae grow deep on the reef, below the level at which reef-building corals can survive, where they contribute significantly to reef growth and sand production.
One recognizable green macro-alga that can sometimes be seen on shallower reefs is Halimeda, a heavily calcified alga made up of chains of green disks, each the size of a small button. These disks are calcium carbonate, like coral, and in some areas Halimeda rubble is a major component of the reef substrate.
Sometimes an inshore reef will merge with shallow beds of turtle grass, one of the very few true marine plants. These grassy beds provide an environment for seahorses, pipefish, damselfish, wrasses, and the young of some reef fishes, including butterfly-fish, as well as small crustaceans, mollusks and worms. The sea grass also provides forage for the rare dugong (Dugong dugon), or sea cow, which ranges across Indonesian waters.
Plankton
The diver will rarely see plankton, and if he or she does, it will usually be apparent as a cloudiness of the water, or an irritating backscatter in photographs. But plankton is an important link in the reef food chain. Reef areas rich in plankton will be characterized by an abundance of filter-feeders, animals that have evolved methods of sifting or snaring plankton from the current—including soft corals, mussels and oysters, anemones, crinoids, gorgonians and sponges.
Plankton consists of both "plants"—phytoplankton—and "animals"—zooplankton, and the larger zooplankters are predatory on the diatoms and algae of the phytoplankton. The plankton also contains some temporary members, the meroplankton, which consists of the larval stages of fish and invertebrates. As these grow, they settle out СКАЧАТЬ