Channels or Kandus

These are gaps or breaks in the outer reef of the Atoll where the tidal and ocean currents wash onto and off the central lagoon, often creating a hot spot of action especially during periods of good current. It is not uncommon to see large numbers of Grey or White tip sharks or large squadrons of Eagle Rays effortless riding the incoming ocean streams in the channel mouths.

A Tila is a submerged Coral Reef, typically with a flat surface coming to between 9 and 12 meters of the surface. The sides often have small caves and overhangs. These present some of the most interesting and exiting dive sites as they attract a huge number of schooling fish and hard and soft coral growth. Tilas are found both inside the Atolls and in the channels.

These are generally smaller round coral reefs that come within a few meters of the surface, although still submerged. Similar rich environments to a Tila, often with caves, overhangs and swim throughs.

The fringing reef generally starts at around 2 meters depth, shelving down to a forty meter shoulder and then plunging into the ocean depths. Being on the outside of the Atoll, the Outer Reef is subject to passing traffic. This is where Whalesharks, Mantas, Hammerheads and giant Tuna cruise above the deep water on the outer fringes of the Maldives.

DIVE SAFETY

To enhance the enjoyment and safety of a dive, consideration of the direction and strength of currents is extremely important, wherever you are diving; whether it is in the 'Kandu', a pass between the atoll reefs or 'Tila', a shoal, inside the Atolls. The success of a dive almost always depends on these variables.

The Maldivian archipelago is swept by ceaseless currents caused by the monsoons; generally East to West during the Northeast monsoon, from December to April, and West to East during the Southwest monsoon, from May to November. However this is not a hard and fast rule, as changes in wind directions and tides can offset the influence of the oceanic currents - especially so during the transitional period between the two seasons.

Further, the location of islands, reefs and 'Tilas' cause great irregularity in the flow of current streams inside Atoll passes. Many local boat captains show great skill in telling the direction of the current by observing tiny ripples or wave patterns on the surface. However, the dive guide often jumps into the water to determine the exact strength and direction.

Strong currents often make a dive site livelier, and that makes the additional effort worthwhile.

Tides

Tides are an important aspect to consider when diving. Tides often determine the strength and direction of the currents and often visibility depending on where you dive. A rising tide brings in clear waters from the ocean into the atoll, while receding tides carries out less clear water from inside the Atolls. For instance a drift dive through a channel, taking advantage of rising tide and clear water flowing into the Atoll would offer an exciting dive with high visibility. Therefore, even though it may be easier to dive in slack waters at high or low tide, it does not always provide the most exciting of dives.

The time between successive high tides is approximately 12 ½ hours and divers may take the advantage of the tides depending on the time of the day when the tide moves.

Spring tides cause the maximum variation in tides - highest at 110 centimeters. On the other hand during neap tides the variation can be just a few centimeters.

CORAL BLEACHING

Coral bleaching refers to a process in which corals expel the algal cells that normally live within their tissue. These algae give corals their characteristic brownish colour and once they have been expelled, the white skeleton shows through a coral’s transparent tissue, giving it a bleached white appearance. Bleached coral looks very similar to coral that has recently died, but can be distinguished (on close inspection) by the presence of small polyps and tentacles on the coral surface.

Coral bleaching can be caused by stressful environmental conditions such as extreme temperature, low salinity, extreme light and various toxins. However, large scale bleaching episodes are usually associated with unusually high sea temperatures. This relationship has led to the suggestions that coral reefs are showing early signs of stress due to global warming caused by green house gas emissions.

Bleached corals are still alive and can recover fully if the stressful conditions are not too severe or prolonged. However massive coral mortality is a feature of many severe bleaching episodes. The events of 1982/83 and 1998 in particular resulted in wide spread mortality of some coral in some areas around the world. Following milder bleaching events, most coral recover their health, but this may take several months, and can result in lower growth and abnormal reproduction for some time after normal colour has returned.

Coral Reefs are made up of millions of tiny sea creatures called polyps. Polyps are very closely related to the jellyfish and sea anemones and like the anemones they possess tentacles for catching their prey. They are colonial creatures with hundreds of polyps in a single coral colony and they co-exist with algae in a symbiotic union. Each polyp secretes an exoskeleton of chalk which forms the basis of the reef and they are filter feeders catching tiny food particles with their tentacles. The algae are able to produce nutrients by photosynthesis and give each coral its distinctive colour.

Coral reefs are almost exclusively located in tropical seas. This is because of the conditions required by the corals in order to sustain growth, which are:

• Bright sunlight - to enable photosynthesis
• Warm water - optimal growth is between 24 - 32 °C
• Clear water - allows light penetration. Heavily silted water will choke the corals
• Shallow seas - sunlight cannot penetrate sufficiently below 100 meters to allow reef growth

Coral reefs are unique structures built up over many years. They flourish in the warm waters of the tropics, fringing islands and continents, and forming Atolls far out in the ocean. Some are like beautiful gardens, paved with delicate corals and home to innumerable brightly colored fish. Others are full of drama, with massive coral formations extending into deep water with sharks patrolling along the reef edge.

CONSERVATION

Sadly, like virtually every other natural habitat, coral reefs are coming under intense pressure. Many have been polluted and choked with sediment and rubbish washed from the land. Others have been damaged by coastal development, coral mining, over-fishing and collection of reef animals. Tourism too has an impact, but you can help to minimize the damage.

Nowadays more and more people are visiting coral reefs, to look at their amazing variety of colorful life. Unfortunately, all over the world reefs are suffering from too many visitors. Corals that take years to grow are being damaged or destroyed in an instant.

Remember these basic rules and help us to preserve the reefs around Addu Atoll.

• Don't touch corals, rest on them or kick them. Corals are living animals and are damaged even by gentle handling.
• Avoid kicking up the sand. It spoils the visibility for other visitors and damages corals and other reef animals when it settles.
• Do not spearfish. This is now prohibited in most countries and spear guns are usually confiscated by Customs officials.
• Leave all corals and reef animals where they are. Corals are the 'building bricks' of the reef. In many areas shells and other reef animals have become rare because too many people are taking them. Many tourist resorts and dive operators ban collecting.
• Make sure you are properly weighted!
• Take great care in underwater caves and caverns. Avoid crowding into a cave and don't spend too long there. Bubbles collect in pockets on the roof of the cave and the delicate reef animals there can 'drown in air'.