Shark Point this morning was absolutely amazing! We saw a group of twenty bump-head parrot fish, at least fifteen turtles, a black-tip reef shark and tons of colorful reef fish! Continue reading
What is coral bleaching?
A coral colony is made up of numerous individual coral polyps. Corals use their tentacles to feed on zooplankton, but depend primarily on microscopic, algae known as zooxanthellae located inside their tissues to provide them with food. Corals are very dependent on this symbiotic relationship, receiving up to 90% of their energy from the zooxanthellae. Healthy corals usually appear tan, brown or green from the presence of the algae within their tissues. Some types of corals have additional pigments so may appear more blue or purple.
Coral bleaching is a stress response that occurs when the coral-algae symbiotic relationship breaks down. The term “bleaching’ describes the loss of color that results when zooxanthellae are expelled from the coral polyps or when chlorophyll within the algae are degraded. When the zooxanthellae leave the coral, the white of the coral skeleton is then clearly visible through the transparent coral tissue, making the coral appear bright white or ‘bleached’. Some corals, such as our lobe coral, have additional pigments in their tissue, so when they ‘bleach’ they may turn a pastel shade of yellow, blue or pink rather than bright white.
What causes coral bleaching?
Coral bleaching can be caused by a wide range of environmental stressors such as pollution, oil spills, increased sedimentation, changes in salinity, low oxygen, or disease. However, the primary cause of mass coral bleaching is increased sea temperatures. Corals are very sensitive animals so water temperatures need only increase 1-2 degrees Celsius above normal levels for bleaching to occur. The corals are still alive after bleaching but begin to starve. Most corals struggle to survive without their zooxanthellae. If the stressful conditions return to normal rather quickly, the corals can regain or regrow their zooxanthellae and survive. If the stressors are prolonged, the corals are more susceptible to disease, predation, and death because they are without an important energy source.
Not all corals are equally susceptible to bleaching. Fast-growing branching and plate corals are often the first to bleach and are more likely to die from bleaching. Slower growing massive corals usually take longer to bleach and tend to be able to survive for longer in the bleached state.
Past, Present… Future?
Localized coral bleaching has been recorded for over 100 years but only in the last 20 years have we seen mass coral bleaching events. Mass bleaching has now affected every reef region in the world. A particularly severe worldwide bleaching event occurred in 1998, effectively destroying 16 percent of the world’s reefs.
When coral bleaching causes extensive death of corals, recovery is very slow and dependent on new, young corals (called recruits) settling and growing on the reef. Regrowth of reefs that have been severely damaged by bleaching may take decades. Recovery is especially difficult for reefs in locations suffering from other stresses such as pollution, overfishing or other chronic pressures. The last coral bleaching event was in 2010 around the Gili Islands. A lot of corals specially in the shallow parts of Hans Reef, Halik and around Villa Ombak were highly affected.
Coral bleaching is predicted to occur much more frequently due to higher sea temperatures associated with global climate change. Human populations continue to grow placing more and more stress on the coral reefs. The time to protect our reefs is NOW before these valuable resources are lost forever.
When you are diving around the Gili Island you will spot them on every dive site. Some people loves them other one say this one of the most ugly fish in the sea. We are talking about the Parrotfish.
This herbivorous fish uses its strong beak-like mouthparts to scrape algae and other plant matter from the surface of the coral. This maintains the health of the reef by keeping algae in check, which could otherwise overwhelm the delicate reef ecosystem.
An unusual feature of parrotfishes is that they are able to change sex, with females becoming fully functional males. In a population, parrotfish start off as either females or males (known as primary males). Females may at some point in their life become male (secondary males). Populations that have these two types of males are called ‘diandrous’, meaning ‘two-males’. A terminal phase male defends a territory and a harem of females. If the male should die, the most dominant female will become the dominant male, her ovaries becoming functional male testes.
The parrotfish occurs in the western Atlantic, from Florida, Bermuda and the Bahamas to Argentina and the Gili Islands Indonesia.
Associated with coral reefs at depths of 3 to 25 metres. At night, parrotfish retreat into crevices. Juveniles tend to occur in mangroves adjacent to the reef. The mangroves act as important nursery areas and provide food-rich and predator free safe-havens for the growing young.
Porcupinefishes are on every dive site around the Gili Islands. You will find the for example when you are diving North Gili Air, on Hans reef. But is the Porcupinefish the same fish as a Puffer fish?
Porcupinefishes are similar to puffer with regards to their ability to inflate by drawing water into the addomen. They have additional protection in the form of sharp spines on the head and body. These are either three rooted or non movable as seen in the burrfishes or two rooted and erectile in Diodon. In the genus Lophodiodon both types of spines are evident on the same individual. Typically the spines of Diodon lie flat against the body with their tips directed posteriously, but if theatened the body is expanded and the spines are erected approximately perpendicular to the body surface, forming an obvious deterrent to potential predators.
Porcupinefishes and burrfishes further differ from puffers in having broader pectoral fins, in lacking a median suture on their dental plates and having larger eyes.
Most are nocturnally active, usually hidden in caves or beneath ledges during daylight hours. Their strong dental plates and powerful jaws are well suited for crushing the hard outer shell or test of sea urchins, gastropod molluscs and hermit crabs as well as exoskeleton of crabs. Care should be exercised when handling these fishes because of their obvious spines and capability of inflicting severe bites.
They are also reports of poisoning due to people eating diodontid fishes presumably from tetrodotoxin but they can also cause ciguatera.
The Family contains 6 genera and 19 species which occur in all tropical subtropical and warm temperate seas.
A lot of times you see them around when you are diving Sharkpoint, Gili Trawangan or Bounty Wreck, Gili Meno. Its the Batfish. They are so common when and we see then so many times around the Gili Islands, but what do we know about them?
Batfishes are recognisable on the basis of their distinctive shape, particulary juveniles, which have greatly elevated dorsal and anal fins. Other characteristics include a small, terminally located mouth, brush like jaw teeth (often with tricuspid lips), a continuous dorsal fin with 5-9 spines and 19-40 soft rays, anal fin with 3 spines and 17-29 rays, and typically a silvery adult colour pattern often with dark bars on the head and body.
Members of the genus Platax are extremely tame and curious, often approaching divers at close range.
Young fish are found close to the bottom, often around boat moorings, docks, jetties, and floating objects. Adults may form midwater feeding aggregation, frequently adjacent to steep outer reef slopes.
The diet consists largely of benthic invertibrates and zooplankton.
In their natural habitat the young of P. orbicularis mimic dead leaves, and those of P. pinnatus mimic toxic polyclad flatworms that are nearly identical in colour and shape.
Diving around the Gili Islands gives you the oppurtunity to see unusual fish, like the Razor fish. You will find the in the harbor of Gili Air, in the front of Oceans 5 dive resort.
These are small, unusually shaped fish that are related to pipefish and seahorses. They are characterised by an extremely thin or flattenend and nearly transparent body, which is encased in an integument of thin, sutured plates. The unusual appearance is further enhanced by their peculiar vertical orientation with the snout pointing downwards. However they are capable of rapid bursts of horizontal swimming when chased by a diver or preditor. Razor fish often occur in large synchronised groups, sometimes containing more than 50 individuals. The family is restricted to the tropical Indo Pacific region and contains two genera and four species, 3 of which occur in the East Indian region.
The fish’s diet consists of a variety of zoo-plankton and minute crustaceans. When in captivity, it is fed bait shrimp and a variety of small, live marine food. It swallows its food whole. This fish, like its closest relative, the seahorse, is toothless. As a young fish, it is prey to many larger fish. As an adult, however, the fish is thought to have little, if any, predators. This is thought to be because of its great camouflage and its “armor”. The life span of the fish, unlike the reproduction method, is unknown.
Maximium size to about 14 cm. Pale yellowish brown on the back and white on lower half with dark brown to black stripe from snout, through eye, to base of caudal fin. Sometimes seeks refuge among sea urchin spines.