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A coral reef is a sea structure made out of living organisms which together form a wall.
Stony corals are usually the main organism found in a coral reef, but other types of skeletal material also join together to form the thick walls.
A coral reef is also "constructed" by the thousands of fish, sponges, and sea urchins grazing around the area. As these organisms move about, they actually help the coral reef settle and gain a more stable structure. Waves are also partly responsible for the size and format of a coral reef, as they affect the geology of the formation.
Coral reefs begin to form when free-swimming coral larvae (planulae) attach to the submerged edges of islands or continents.
A fringing reef is one of the three main types of coral reefs recognized by most coral reef scientists. It is distinguished from the other two main types (barrier reefs and atolls) in that it has either an entirely shallow backreef zone (lagoon) or none at all. If a fringing reef grows directly from the shoreline, the reef flat extends right to the beach and there is no backreef.
There are two main components that make up a fringing reef, the reef flat and the reef slope.
Reef flat
The reef flat is the shoreward, flat, broadest area of the reef. The reef flat is found in fairly shallow water, and can be uncovered during low tide. This area of the reef is only slightly sloped towards the open ocean.
Since the reef flat is adjacent or nearly adjacent to land, it sustains the most damage from runoff and sediments. Typically, few of the flat's corals are alive. Seagrasses, seaweeds, and soft corals are often found there.
Reef slope (Fore reef)
The reef slope is found at the outer edge of the fringing reef, closest to the open ocean. This area of the reef is often quite steep and descends either to a relatively shallow sand bottom or to depths too great to allow coral growth.
Coral grows much more abundantly on this slope, both in numbers and in species diversity. This is mostly because runoff and sediments are less concentrated here. Greater wave action disperses pollutants and carries nutrients to this area.
The upper portion of this slope is called the reef crest. The crest has the best balance between sunlight and waves, so coral grows fastest here. The base of the slope receives the least sunlight and has the least growth out of the whole slope.
Fringing reefs, which are the most common, project seaward directly from the shore, forming borders along the shoreline and surrounding islands.
The fringing reef coasts of Kenya and Tanzania, comprising platforms with bars at their ocean
margins, are modifications of a geomorphology created during the Pleistocene period by the
extensive coastal accretion and partial erosion of calcium carbonate sediments occurring now
as limestones.
The prime fringing reefs of Kenya and Tanzania are situated on coasts that are exposed to the open ocean, and where there is an insignificant discharge of terrigenous sediment from the hinterland.
In Tanzania, fringing reefs feature particularly on the eastern shores of the Zanzibar islands.
The present-day geomorphology of these reef coasts has been inherited from a long history of carbonate sedimentary development and degradation at the land-ocean boundary.
Threats
Humans are the biggest threat to the integrity of a coral reef. Because of pollution, boat traffic, and aggressive fishing, coral reefs are now considered in danger and are protected under the Great Barrier Reef Marine Park Authority, an Australia-based institution.
The illegal trade on saltwater aquarium fish is also a major factor on coral reef destruction, as little can be done to stop collectors from around the world to request exotic, pricey species.
A coral reef is also susceptible to major environmental changes, including global warming, which affects water currants and marine migration. Coral bleaching, a form of erosion, occurs when water temperatures reach higher-than-normal levels. This can prove disastrous for a coral reef.
Important
Avoid all contact with corals as they are very delicate animals and even a gentle touch can cause them harm. Corals can sting and cut .
Keep interaction to a minimum. Do not touch, handle or feed marine life.
Take nothing living or dead out of the water, except garbage.
TO LOG THIS EARTHCACHE:
- you NEED TO GO TO THE GIVEN CO-ORDINATES on Jambiani beach
(where you can easily log the regular cache 'Pakachi Borderline' also!)
- send in answers to the following questions and WAIT FOR APPROVAL
1. At the given coordinates you can even 'walk' from the beach to the reef at low tide. Estimate the distance between the beach and the coral reef at this spot.
2. There are basically no coral reef structures on the American west coast or on upper Asia, including Russia. This is mainly due to two reasons. What are these reasons?
3. How many different species of fish did you see when snorkelling the Zanzibar reefs?
Optional, log with a/some picture(s) of your snorkelling activities
Additional Hints
(No hints available.)