Recommended
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.
For a safe walk remember to bring with you a pair of plastic sandals.
Take nothing living or dead out of the water, except garbage.

Reefs of Zanzibar
Zanzibar is located close to the equator where the water temperature never falls below 16C. That has permitted the local coral reef to richness develop. The fringing reef, which is present on most of the islands forms a near continuous ridge that provide a breaker from the sea creating extensive lagoons of shallow clear water and warm sunny climates.
Islands of the archipelago do themselves consist of corals as these structures, built over millennia, have been left high by falling sea levels and uplifting land masses, now forming a significant proportion of the islands, especially in Eastern Unguja.
The reef protects the islands from erosion by the waters of the Indian Ocean and provides a habitat for marine life.
At low tide, villagers spread across the shimmering waters to fish and, in the seaweed cultivation areas, to tend their crops and walking out over the reef at this time is stunningly beautiful.

About corals
The familiar structures that we recognise as coral are actually the accumulation of the skeletons of billions of tiny coral animals, or polyps. Living polyps inhabit the surfaces of these structures atop successive layers of their ossified ancestors. They consist of a stalk, the bottom of which is anchored to the colony by a skeletal cup, created by the excretion of calcium and into which it will withdraw for protection. At the upper end of the stalk is a flattened oral disc with an opening, surrounded by tentacles and cilia, which is both the mouth and anus.
The food chain of the reef is focused around the symbiotic relationship between the coral animals and algae, providing the primary source of food production. Zooxanthellae for instance are single-celled, round algae which live inside polyps and generate their food energy by photosynthesis. At night, the coral feeds with zooplankton. The zooplankton is valuable for the phosphorus it contains which is cycled back and forth with the zooanthellae in return for food. This kind of symbiosis, where all parties benefit from and are often dependent upon the relationship is known as commensalism.The photosynthetic nature of the zooxanthellae means that the coral with which it undertakes this relationship must live in a location where adequate light is present, that's why coral reefs only thrives in shallow clear water and warm sunny climates. Other types of colonial coral which do not depend upon the zooxanthellae for food can be found in the deeper waters beyond the reef.
Coral reproduction is one of the great sights of nature. Unlike most animals, who specialise in the production and rearing of a small number of young, coral employs a very different strategy. Remarkably, the reproduction of every tiny polyp in the colony is timed to coincide, usually on one night each year, and synchronised by the motion of the moon. On the selected night, one by one each polyp ejects a puff of eggs and sperm until the water is clouded with billions upon billions of nascent animals drifting at the mercy of the current. The timing of the release is such that the eggs should catch an outward flowing current, taking them out to sea to both extend the existing colony and to colonise new shores.
The food chain of the reef environment continues upward with herbivorous creatures, such as sea urchins, sea cucumbers, molluscs and many species of often colourful fish, which feed on the coral algae. Amongst the fish commonly seen on local reefs are clownfish, moorish idols, angelfish, threadfin, snapper, sturgeon, wrasse and the poisonous lionfish. Predators hunting on the reef, such as crabs, eels and rays, make use of crevices and caves to surprise and capture their prey, whilst sharks, turtles, rays, dolphin and barracuda sweep the deeper waters.

Coral reef types
There are 3 main types of reefs. The fringing reef, the barrier reef, and atolls. Fringing reefs, which are located close to the shore, are separated from land by shallow water or no water at all. They border shorelines of continents and islands in tropical seas and are commonly found in the South Pacific Hawaiian Islands, and parts of the Caribbean.
Barrier reefs occur farther offshore creating lagoons that separate them from land. They form when land masses sink, and fringing reefs become separated from shorelines by wide channels. Land masses sink as a result of erosion and shifting crustal plates of the earth. Barrier reefs are common in the Caribbean and Indo-Pacific. The Great Barrier Reef off northern Australia in the Indo-Pacific is the largest barrier reef in the world. This reef stretches more than 1,240 miles (2,000 km).
Atolls are are ring-shaped reefs that surround a central lagoon and they are found far offshore. When the land mass of a small island disappear below the ocean surface the reef becomes an atoll. The result is several low coral islands around a lagoon. Atolls commonly occur in the Indo- Pacific. The largest atoll, named Kwajalein, surrounds a lagoon over 60 miles (97 km) long.
Existing coral reefs have been formed since the last glacial period in the Pleistocene epoch, 10.000 years ago. Seawater trapped as ice in enormous glaciers caused sea level to fall. Consequently, all previously formed coral reefs probably died from exposure. When the glaciers melted, sea level rose to its current position and present-day reefs began to develop.