Preliminary results indicate that while all surveyed reefs are experiencing bleaching in this region, the level of community-wide bleaching ranges from ’minor’ to ’extreme’. The scientists have also noted that the extent of bleaching differs between reefs and between species in the same location
Scientists report that the bleaching severity on the central and northern GBR has varied between reefs. Mortality and severe bleaching was not observed until Saxon and HastingsReefs near Port Douglas.
On reefs off the coast of Townsville, bleaching is generally restricted to the shallow, high-light environment of the reef flat (upper 1-3m, on top of the reef). Reefs experiencing this ’minor‘ level of bleaching (1-10% of coral community bleached) are typically less likely to experience major loss to the coral community.
On mid-shelf reefs along the coast from Mission Beach to Innisfail, bleaching levels are ’minor’ to ’moderate’ with less than 10-30% of the community bleached and bleaching restricted to the upper reef flat (1-3m).
AIMS researchers have observed an increase in bleaching severity on reefs north of Cairns, with extreme bleaching (more than 60% of the community) observed at Saxon and HastingsReefs. Both of these reefs are reported to show bleaching of a wide range of species, extending beyond the reef flat to depths of 10-15m.
In addition, scientists have observed that different species of coral have responded to the same local (that is, reef level) heat stress conditions in different ways. On reefs with ’minor’ bleaching, bleaching is somewhat restricted to coral types known to be more sensitive to thermal stress, such as Seriatopora, Stylophora and Pocillopora species (see below). Reefs exhibiting a ’moderate’ level of bleaching appear to impact a higher diversity of taxa including branching and plating Acropora species, some massive Porites, and a wide range of moderately tolerant sub-massive species including Goniastrea, Favia and Favites