About Coral Atolls

Atolls are low coral islands which lack volcanic or continental rock in their surface geology. Most of the worlds atolls are located in the tropic Pacific. Atolls have irregular but generally circular or semicircular reefs surrounding a lagoon. Some lagoons may be open on one side or there may be a single reef island without a lagoon. Most atolls in the Pacific lie in clusters or chains within a broad belt which runs in a generally south eastern direction.

Atolls are built by active coral and coralline algae growth on the tops of submerged inactive volcanoes and sea mounts, and their location and structure is influenced by ocean floor movements, changes in sea level and wave action. Some or all of an atoll's reef and sand flats are exposed during low tides and covered during high tides. The windward beaches have ramparts of scattered coral rubble and sand and/or cemented beach rock. Lagoons may be shallow or deep and may vary in the amount of formation of new coralline structures depending on depth, siltation, circulation, etc. The presence of deep ocean passes may allow ships to enter sheltered lagoons, but a few atolls have no passes, and at such islands, ships can only load and unload on the lee side during calm weather using small boats or canoes to lighter cargo across the reef.

Lagoon size, circulation, reef area and structure influence the availability of rich shallow marine resources that may or may not be intensively exploited, depending on the size of the human population. There are also a great variety of deeper water and pelagic fish that require investment in lines, sailing, canoes etc. Atoll dwellers have developed highly adaptive systems of sea and reef tenure to manage and conserve their marine resources.

To exploit the rich marine resource base requires land-based resources such as wood and plant-fiber as well as food plants. These, of course, depend on the amount of availability of fresh water and the nature of atoll sands and soils. Being low, atolls receive approximately the same amount of rainfall, and the evaporation rate, influence the thickness and the reliability of the fresh water lens, which is somewhat thicker towards the center of an island and thinner on the edges where the groundwater may be brackish. Wider islands in areas of adequate and steady rainfall generally have thicker and more stable freshwater lenses which support lush and more varied vegetation and the formation of somewhat thicker humus and soil. Salt tolerant plants like coconut and pandanus grow adequately on drier atolls but other important food plants like breadfruit and taro require a stable lens to be productive. Droughts and typhoons may have a devastating effect on atoll dwellers' food resources. Larger and wetter atolls support larger populations, but most atolls have heavy population pressure.

People living on atolls have developed complex and flexible land tenure systems with a variety of ways of managing and assigning land rights and other resource rights.

An issue of vital concern to atolls is world sea levels. Many climatologists claim that sea levels are rising owing to the melting of polar ice due to the reducing ozone layer in the atmosphere. Predictions vary, but some expect a one meter rise in the next 40 to 50 years. This could make many atolls uninhabitable in their foremost form because what matters is not the general sea level, but the level in times of vulnerability during spring tides, hurricanes, tsunamis etc. The other negative effect of such a rise is the reduction of the fresh water lens.

Compensation for this possible disadvantage is the increasing benefit atoll people are receiving from living resources in the area. This has been greatly facilitated by the recognition of the 200 miles Exclusive Economic Zones and by advances in technology - as well as by the shortage of protein foods in the Pacific rim nations. Tuna is the main product at present, but there are many other exploitable fish and other marine life species. Within the lagoons, pearl culture has become the main economic resource in some of the atolls, and seaweed is often grown for pharmaceuticals. Mineral exploration has demonstrated the existence of manganese, cobalt and other minerals on the Pacific seabed.

Background Photo: The Kio flower

Also See: Atoll Nation