Siaba Besar is located to the north of Rinca Island, and is home to another great drift dive. Best dived on a falling tide, when the currents will carry you south towards a beautiful coral garden, Siaba Besar can nonetheless be attempted in reverse with relative ease. With a falling tide, begin the dive at the northern tip of the island. Follow the reef slope down to 20-24m, where a series of dynamic overhangs wait to be explored. Moving on with the reef on your left, you will drift past strikingly colourful soft corals, delicate black corals, sponges and a huge diversity of hard corals. Batfish, grouper, snapper and sweetlips hide in and around the overhangs, while hawksbill turtles, whitetip reef sharks, and barracuda are regular visitors to this site. Towards the end of the dive there can be a moderate current drawing you away from the island. Remain close to the reef to avoid being drawn out into the channel. The coral garden is particularly vibrant at the southern end of the island, and is an ideal spot to explore during your safety stop. Patches of green, purple and brown staghorn corals extend as far as the eye can see. Hidden amongst them, careful observers may catch a lucky glimpse of the elusive Mandarin fish. Be warned—these little gobies are difficult to spot despite their bright colours, but patience rewards with the incredible sight of these vivid, multi-coloured fish. For the best chance to find them, hover stealthily over the corals and carefully watch the shadows amongst the branching corals. In the late afternoon you may even see Mandarin fish leaving the safety of their coral homes to mate.
The green sea turtle (Chelonia mydas), also known as the green turtle, black (sea) turtle, or Pacific green turtle, is a large sea turtle of the family Cheloniidae. It is the only species in the genus Chelonia. Its range extends throughout tropical and subtropical seas around the world, with two distinct populations in the Atlantic and Pacific Oceans. The common name comes from the usually green fat found beneath its carapace. This sea turtle's dorsoventrally flattened body is covered by a large, teardrop-shaped carapace; it has a pair of large, paddle-like flippers. It is usually lightly colored, although in the eastern Pacific populations parts of the carapace can be almost black. Unlike other members of its family, such as the hawksbill sea turtle, C. mydas is mostly herbivorous. The adults usually inhabit shallow lagoons, feeding mostly on various species of seagrasses. Like other sea turtles, green sea turtles migrate long distances between feeding grounds and hatching beaches. Many islands worldwide are known as Turtle Island due to green sea turtles nesting on their beaches. Females crawl out on beaches, dig nests and lay eggs during the night. Later, hatchlings emerge and scramble into the water. Those that reach maturity may live to eighty years in the wild. C. mydas is listed as endangered by the IUCN and CITES and is protected from exploitation in most countries. It is illegal to collect, harm or kill them. In addition, many countries have laws and ordinances to protect nesting areas. However, turtles are still in danger because of several human practices. In some countries, turtles and their eggs are hunted for food. Pollution indirectly harms turtles at both population and individual scales. Many turtles die caught in fishing nets. Also, real estate development often causes habitat loss by eliminating nesting beaches.
Bleaching occurs when corals expel their symbiotic zooxanthellae - pigmented, algae-like protozoa that live within the coral's cells. High temperature, pollution or other stresses can cause the coral to expel its zooxanthellae, leading to a lighter or complete loss of color.