In 1998, there was a global mass bleaching event where the Great Barrier Reef Marine Park Authority (GBRMPA) reports that 50 per cent of the reefs on the Great Barrier Reef suffered bleaching. The coral reefs around Magnetic Island were among those that were badly affected by this global bleaching event that was linked to El Niño and Global Warming. Sea temperatures in 1998 were the highest ever recorded at that time. There was another mass bleaching event reported in 2002 but this event was not evident on the reefs of Magnetic Island, possibly because those corals that are most susceptible to bleaching were killed off in the previous 1998 event and had not regrown or substantially recolonised.
Mass coral bleaching was again reported in the Great Barrier Reef (GBR) over consecutive years in 2016 and 2017 by the ARC Centre of Excellence in Coral Reef Studies. In 2016, severe coral bleaching was largely restricted to the northern GBR from Cairns to the Torres Strait. This year more bleaching has been observed in the central GBR, from around Townsville to Cairns, which the previous year had escaped widespread severe bleaching. Nearshore reefs in the Palm Island group, just north of Townsville, were included in those reefs most severely affected by coral bleaching.
Recent observations, in April 2017, indicate that the coral reefs around Magnetic Island may have dodged the bullet that has struck neighbouring island reefs. Previous surveys of Geoffrey Bay reef in 2014, fifteen years after the disastrous 1998 mass bleaching event, indicated that corals were recovering well. Many of the plate-forming and branching corals that were killed in 1998 were well developed again in 2014.
As of April 2017, no obvious evidence of recent coral bleaching was observed along a 1 km stretch of reef at Geoffrey Bay. This reef remains one of the best developed inshore coral reefs around Magnetic Island and a wonderland for snorkelers. Both coral species diversity and coral cover remains relatively high considering the nearshore location of the reef. Video footage of corals around the wreck of the Moltke can be seen by clicking here. However, the risk from more frequent and intense bleaching events caused by global warming and elevated water temperatures remains, made still more serious by water quality concerns from river runoff and dredging for a proposed port expansion in Townsville.
The corals in Alma Bay have not fared quite so well and there is some evidence of recent coral bleaching. However, partial or complete bleaching was only observed in five coral colonies out of hundreds and Alma Bay remains an accessible location to enjoy snorkelling. Both corals and fish remain abundant in this small bay. It may be that the small size of the bay and reduced water circulation increased its susceptibility to coral bleaching, over that of Geoffrey Bay.