Nothing quite matches the surprise of a coconut crab dropping onto the dinner table and trying to steal your fish.

I subsequently learned from Chumbe Island ranger Yusuf Omar that he has seen coconut crabs - also known as robber crabs - carrying off dirty plates from the kitchen. Smelling food, one determined female, using powerful pincers normally used for husking coconuts, even sliced through an aluminium cooking pot to get to the rice inside.

Endangered elsewhere in the world, these ponderous crabs flourish on Chumbe, where they engage in nightly scuffles with hermit crabs for scraps of food.

Chumbe Island Coral Park (CHICOP) is the single-handed creation of German-born Sibylle Riedmiller who worked in many African countries before settling in Tanzania fifteen years ago. A specialist in educational studies with diving and sailing interests, Sibylle called at Chumbe during a visit to Zanzibar and, enthralled by its pristine state, set about gaining IUCN recognition to ensure its environmental protection. This was granted in 1994 under the auspices of the Zanzibar Department of the Environment.

The following year, she purchased the island on a 33 year lease.

While still largely unknown to tourists, visiting scholars are quick to recognise the value of Chumbe. Writing to Sibylle, the Chief Scientist at the Australian Institute of Marine Science in Townsville, Professor J E N Veron, had this to say:

"I have worked extensively on the major coral reefs of Australia, South East Asia, the Pacific, Red Sea and the Caribbean and in 3O years I cannot recall seeing the likes of the coral community I saw recently at Chumbe Island. Small though it is, it has at least 90% of all coral species that have ever been recorded from eastern Africa."

Chumbe is distinguished from other off-shore islands by a lighthouse soaring above its forest canopy. Raised in 1904, the tapering beacon was manned by Indians who built a tiny mosque, complete with a carved teak pulpit, on the southern headland. Thanks to the lighthouse Chumbe enjoyed army protection and, although thousands of people passed it daily on the way to Dar-es-Salaam, no one ever came ashore.

Today's only cause of potential stress to the sanctuary is when hydrofoils carrying ever increasing numbers of tourists to Zanzibar pass too close to shore. Departure for Chumbe is from the Mbweni Ruins Hotel beach. A motorboat picks you up for the 40 minute voyage passing traditional sailing boats. These are allowed to fish anywhere except off the west coast of Chumbe where an area of 200 metres seaward is gazetted as a Marine Reserve.

Snorkelling along one of the marine trails in the company of a ranger is the highlight of a visit to the island. An uninterrupted coral garden lauded by Professor Veron as "the best shallow water coral reef in the world", extends from the beach to a drop-off about 16 metres deep .

It is a snorkeller's paradise. Elsewhere in the world corals are dying at an alarming rate, but here they are regenerating: mauve, pink, yellow and blue coral; fan, fire, brain and mushroom coral growing in a well manicured underwater garden.

Living and breeding without harassment, 370 species of fish have been recorded on the protected reef. I saw damsel fish, batfish, butterfly cod, angelfish, parrot fish, moray eel, a big potato cod and hundreds of rainbow-like anemone fish in a morning's diving.

Where the turquoise water turns indigo, you look down on passing rays, schools of mackerel, caranx and an occasional turtle flapping lazily by.

Floating Information Modules - red inner tubes attached across the reef - allow you to hang on and marvel at pageant. SCUBA is not allowed and throwing out an anchor is strictly forbidden.

Covering 16 square hectares, Chumbe is composed entirely of deeply weathered coral limestone rag. A few mangrove trees, baobabs and coconut palms grow around the perimeter, but two-thirds of the island is covered by dense evergreen flora rooted in shallow sub-soil in the jagged crevices.

Trees including causarina and pinewood are able to survive on scant water since Chumbe has no natural supply. Snake plants funnel rain down their leaves and others trap droplets caused by the high humidity with aerial roots. Euphorbias display fluted stems designed to reduce water loss. In the central forest, crookedly growing saplings reach towards any light and looping lianas form an impenetrable barrier.

It is in every sense a jungle, but the insect population is low and there are few animals apart from a python brought by Sibylle to eat the rats. Duikers introduced last century for the sultan’s hunting parties are extinct. Only one frog is recorded, but butterflies are common, especially around the yellow flowering Psidia arabica during the long rains when they breed.

Chumbe's forest is explored along a narrow trail hammered out of the jagged coral. From the lighthouse, it winds across the island, around deep grottoes and past huge clams left gaping when the sea level dropped one-to-two million years ago.

Stations placed at regular intervals help to identify each area. Station 14 is a likely spot to hear the warble of the Sombre Greenbul, one of the three most common birds on Chumbe.

Although 60 species have been sighted, the majority of birds are migrants. These include the Spotted Flycatcher and Roseate Tern which breed on off-shore islets. Generally the forest is quiet with the only sound made by hermit crabs rustling the fallen foliage.

While protecting the island's natural assets, Sibylle is developing Chumbe into a unique eco-tourist resort to include accommodation, a restaurant, exhibition hall and educational centre.

The first four "bandas" (traditional huts) are completely constructed of natural materials using coconut fibre rope to lash the beams. Sloping roofs inspired by Toraja houses in Sulawesi act as wind funnels keeping them cool and airy .

Solar panels provide energy and rainwater catchments to supply water to individual cisterns with a 15-25,000 litre capacity. Compost toilets recycle sewage waste through sand filters for use in garden irrigation so that no pollutants run into the sea with its abundant marine life and sensitive coral.

Christine Osborne is a professional photojournalist who owns a successful photographic library in London.

Published in Travel Africa Edition One: Autumn 1997.Text is subject to Worldwide Copyright (c)