Horseshoe Reef first flank

Surveyed 26 September 2018.

The first flank of Horseshoe Reef is exposed to the prevailing wind and sea conditions found within the lagoon of the Great Barrier Reef. Manta tow surveys were conducted on the reef slope. The reef slope is generally vertical dropping off into approximately 20m of water to a moderate sloping reef base composed mainly of soft coral, rubble and reef framework. The reef structure has many features including gullies, caves, overhangs, bommies and continuous wall.

The benthic community was dominated by coralline/turf algae, but soft coral and hard coral were also common. Hard coral cover on the reef first flank was low composed mainly of Porites species. The dominant coral lifeform was massive, but other forms such as encrusting, sub-massive and digitate corals were also present in decreasing order of abundance. Coral bleaching was not present.

The fish abundance on the first flank of Horseshoe Reef was moderate. Conspicuous groups of reef fishes included parrotfish and surgeonfish. Crown-of-thorns starfish were observed on the first flank of Horseshoe Reef at active outbreak levels that may be expected to significantly reduce live coral cover.

Changes in zone-wide live coral cover through time. Points indicate median coral cover in a given survey year. Solid line indicates a moving average taken over three (preceding, actual and following) survey years.

View of the reef slope showing the results of a COTS outbreak. This is a similar scene to that left after a severe coral bleaching event.
A crown-of-thorns starfish (COTS) on the reef slope.
Almost no coral goes untouched by a COTS outbreak.