Nelly Bay Fringing Reef
The Nelly Bay fringing reef abuts the littoral scrub of the bird habitat reserve and is a dry tropics example of rainforest by the reef. The fringing reef of Nelly Bay is one of the most accessible reefs on the Island and has some of the best opportunities for snorkelling.
The Nelly Bay reef is a continental island fringing reef. Fringing reefs grow directly around the edges of rocky continental outcrops such as Magnetic Island and are characterised by wide reef flats followed by a short reef slope into deeper water. This reef runs parallel to the shoreline and is exposed at low tide, while at high tide is seen as a darker area extending out a few hundred metres from the beach. The reef has been built entirely by coral growth over the last 7000 years. Fringing reefs are quite different from the platform reefs found in the outer part of the Great Barrier Reef.
Starting from the beach, there are four major reef zones:
- Inner reef flat-the part of the reef closest to the shore, consisting of sand, coral rubble and algae. This zone is totally exposed at low tide so the animals here must be adapted to frequent exposure and re-immersion.
- Outer reef flat-the seaward half of the reef flat, where scattered live coral colonies grow close to the reef surface to avoid exposure at low tides. Algae is still abundant.
- Reef crest-the zone where the reef flat ends and the reef slope begins. This is the area of highest wave action and vigorous coral growth and is the best place for snorkelling.
- Reef slope-the part of the reef that descends into deeper water. The corals here are protected from waves and never exposed to the air so they may grow very large with many delicate branches.
Nelly Bay Cross Section
High Resolution Version (1.35MB! .pdf)
The reef community at Nelly Bay is composed mainly of corals that are adapted to the turbid water conditions close to the coast. Massive corals with a boulder-like form are common (families Poritidae and Favidae), as are branching and staghorn corals (family Acroporidae) and leaf-like corals (genera Turbinaria and Montipora). The brown seaweed Sargassum is also common, particularly in the summer months. Reefs in this part of the world are frequently affected by cyclones and bleaching events, so the abundance and size of corals on the reef is directly related to the time since the last major disturbance.
The fish community is composed of many species. Most are on the edge of their usual range and are more abundant on the offshore platform reefs. The major families of reef fishes are represented here and some species, such as the golden striped butterfly fish (Chaetodon aureofasciatus) and the bar-cheeked coral trout (Plectropomus maculatus), are specially adapted to these inshore fringing reefs. Large schools of plankton-feeding damsel fishes (Neopomacentrus spp., Acanthochromis polyacanthus) and fusiliers (Caesio cuning) are common along the reef crest and slope, while roving schools of parrotfishes, goatfishes and wrasses can be observed over the reef flat when the tide is high. Green turtles are also common here. The best time to see them is on high tide, early in the morning close to the shore.