There are some examples of recovery from disturbance. For example, while coral cover is still very low in the Herbert Tully sub-region following the severe reductions caused by cyclone Yasi in 2011, increases in the density of juvenile corals indicates reefs are now showing some level of recovery.36 Similarly, two and a half years after cyclone Yasi caused high to severe destruction on a number of reefs between Townsville and Cairns, reef health surveys found some mid-shelf and offshore reefs showing the promise of recovery, with moderate to high levels of small coral colonies evident.58
There is an overall, long-term decline in coral reef condition and resilience.
Figure 8.2 Changes in coral health of inshore reefs, 2008—2013
The coral health index aggregates cover of corals, cover of macroalgae, density of juvenile corals and the rate of coral cover increase. For corals to be considered in good or very condition, they would have a score of 0.6 or more. The figure presents information for inshore reefs only for the Reef as a whole and for the four areas indicated. Source: Reef Water Quality Protection
Plan Secretariat 2014 59
Despite some positive examples of recovery from disturbance, the overall trend for coral reef habitats within the Region is one of long-term decline in health and diversity 36,39,60,61 and therefore resilience. The causes include chronic disturbances such as poor water quality and outbreaks of coral disease, as well as a recent series of acute disturbances such as crown-of-thorns starfish outbreaks, coral bleaching events and cyclones36,39,62,63,64, which have left insufficient time for many coral communities to recover between events (Figure 8.2). In addition to the disturbances mentioned above, at a local or individual reef level many lower risk threats, such as anchor damage and vessel groundings, can also impede recovery (see Section 9.3.7).
Frequent disturbances and chronic stresses reduce the potential for reef recovery.
Despite recent reductions in the loads of nutrients and sediments entering the Region (see Sections 3.3.1 and 7.3.11), there is a lag before improvements in catchment management translate into improved marine condition, particularly given the strong influence of extreme weather events in recent years. The projected vulnerability of coral reef habitats to changing climate variables (see Section 6.3.2), combined with other cumulative impacts, means coral reef habitats will face chronic effects plus more frequent and more severe disturbance events.9,42,65,66,67 This will reduce their resilience.15,68