Scientists surprised that reef that survived the hotter holocene is already recovering from 2016 bleaching

The ABC reports today that the Great Barrier Reef is recovering “surprisingly” fast.

Optimism is rising among scientists that parts of the Great Barrier Reef that were severely bleached over the past two years are making a recovery.

Scientists from the Australian Institute of Marine Science this month surveyed 14 coral reefs between Cairns and Townsville to see how they fared after being bleached.

The institute’s Neil Cantin said they were surprised to find the coral had already started to reproduce.

Who would have thought that after 5,000 years of climate change, sea level change, temperature change and super-storms every 200 years — that the Great Barrier Reef would have something left up its sleeve?

Much of the ABC reporting on the Great Barrier Reef damage uses vague terms. If I was feeling cruel, I might call them “weasel words”:

Nearly two thirds of the Great Barrier Reef was affected by bleaching in 2016 and 2017, killing up to 50 per cent of coral in those parts.

So which parts are “those parts”? Did 50% of the corals die in two-thirds of the reef? Or has two thirds of the reef been affected by a small amount of bleaching while a much smaller number of reefs were hit by the apocalyptic 50% death-rate? There must be a better way to describe the damage. As it is, it is a number mush. (If only the ABC had a dedicated science unit they would be able to make sense of difficult concepts like this.)

“What it means is the corals along the entire Great Barrier Reef, are survivors that are going to reproduce earlier than expected which could help drive quicker recovery if we don’t see another heat stress this summer,” he said.

“This is a positive news story for a change for the Great Barrier Reef. We’re seeing eggs and we hope those eggs will lead to somewhat of a successful spawning season this summer.”

When climate-sameness would be remarkable…

The Barrier Reef survived the Holocene peak for hundreds of years, so we might assume that the reef has ways to deal with hotter conditions and changing temperatures. Sea levels in Queensland were 1 – 2 meters higher 5,000 years ago. (Lewis 2012) Super cyclones have been hitting the coast of Queensland for the last 5,000 years and there is no sign that storms are getting worse. (see Nott 2001 and Hayne 2001.)

Corals have survived warmer periods and worse storms

Globally it was hotter 5,000 years ago, and sea levels were a lot higher in Queensland:

From a post in 2012 on 5000 year trends in storms in Australia:

Nott and Hayne studied a 5000 year history of super-cyclones along a 1500 km stretch of North East Australia and concluded that the big nasty ones hit roughly every 200-300 years in all parts of the coastline from 13° – 24°S.

Hayne and Chappell (2001) looked at deposits left from storm surges on Curacoa Island (one of the Palm Islands of far north Queensland). They found that large cyclones have been hitting the coast at a statistically constant rate for 5000 years. This includes the earliest times when the sea surface temperature appear to have been about 1°C warmer (Gagan et al 1998). At Palm Island, sea levels were apparently 70cm higher back in that warm Holocene era (Chappell et al 1983). Somehow the Great Barrier Reef survived.

h/t Dave B. Pat.

Australia’s Great Barrier Reef,

At times may get bleached, but its brief,

And for eons survived,

More than bleaching and thrived,

Which must cause alarmists some grief.

–Ruairi

REFERENCES

Gagan, M.K., Ayliffe, L., Hopley, D., Cali, J., Mortimer, G., Chappell, J., McCulloch, M., Head, M.J., (1998) Temperature and surface water balance of the mid-Holocene tropical western Pacific. Science 279, 1014–1018

Lewis, S.E., et al., Post-glacial sea-level changes around the Australian margin: a review, Quaternary Science Reviews (2012), http://dx.doi.org/10.1016/j.quascirev.2012.09.006 [abstract] (paywalled).

Jonathan Nott1 & Matthew Hayne2 (2001) High frequency of ‘super-cyclones’ along the Great Barrier Reef over the past 5,000 years, Nature 413, 508-512 | doi :10.1038/35097055

Hayne, M. and Chappell, J. (2001) Cyclone frequency during the last 5000 years at Curacoa Island, north Queensland, Australia. Palaeogeography, Palaeoclimatology, Palaeoecology 168: 207-219. [Abstract] [Discussion Hayne and Chappell (2001) ]

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