ECO-EXPEDITIONS

Overview of the Great Barrier Reef

The are three reef types recognised on the Great Barrier Reef:

1. Mainland fringing reefs. These form directly adjacent to the mainland. They are relatively uncommon due to the turbid water conditions close to the coast. Examples of these reefs can be seen near Cape Tribulation, north of Port Douglas.
2. Continental island fringing reefs. These reefs form adjacent to rocky continental islands. There are numerous continental islands along the Queensland coast, mostly found within 25km of shore. Water conditions are often turbid in this zone due to the SE trade winds, and underwater visibility is often in the 5-10m range. There has been extensive reef development around the continental islands, and the reef communities are characterised by sediment tolerant hard corals and high proportions of soft corals.
3. Continental shelf platform reefs. These are massive calcium carbonate platforms that rise up to within a few meters of the ocean surface. Reefs of this type make up the vast majority of the GBR, and are found across the outer two-thirds of the continental shelf where water conditions are best.

In the Northern part of the GBR (north of Cairns), the continental shelf is relatively narrow (~60km), and the shelf edge is very sharp, dropping quickly into 1000m depths. Platform reefs form quite close to the coast (within ~10km), and the shelf edge is lined with an almost continuous line of "ribbon" reefs. The combination of the narrow shelf, restricted water flow due to the ribbon reefs, and frequent strong trade winds, means that underwater visibility is often low to moderate (5-15m) on the mid-shelf platform reefs of the northern GBR. Water quality is excellent on the outer slopes of the ribbon reefs, which are bathed by clear oceanic currents.

As one travels south of Cairns, the continental shelf becomes wider, and the shelf edge drops much more gradually into deep water. Hence, the platform reefs form further offshore, and there are no ribbon reefs along the shelf edge. Near Townsville, the first reefs are found ~60km offshore, and the outermost reefs are ~120km from the coast. At the southern end of the GBR, the first reefs are ~125km offshore, and the outermost reefs more than 200km from the coast! In these areas, the combination of long distance from the coast and free water movement over the shelf means that visibility is usually very good on the platform reefs (typically 20-50m).

Considering these facts, it is clear that trade-offs exist between reef type, water quality and accessibility. As you move south from Cairns, ribbon reefs disappear, platform reefs are found further from shore, water quality improves, and the cost and time involved to access the reefs also increases. Other factors to consider are the proximity of coastal towns that can provide charter vessel services, and the length of time since Crown-of-Thorns starfish affected an area.

Follow the links below to see more detailed information on the reef characteristics and Eco-expedition possibilities in each section of the GBR.

Far-Northern Section

Cairns Section

Central Section

Mackay / Capricorn Section

Coral Sea Atolls and Islands

Click here to see information on the Ecological themes we examine on Tevene'i Marine Eco-expeditions.

Click here to read about our Eco-expeditions Philosophy.