Fossil corals, up to half a million years old, are providing fresh hope that coral reefs may be able to withstand the huge stresses imposed on them by today’s human activity.
If reefs could persist through the massive changes imposed by sharply falling sea levels during the last ice age, they may equally be able to endure human impacts causing equivalent stresses, an international scientific team has found.
Huon Peninsula raised reef terraces (Photo: John Pandolfi).
In the world’s first study of what happened to coral reefs when ocean levels sank to their lowest recorded level – over 120 metres below today’s levels – a study carried out on eight fossil reefs in Papua New Guinea’s Huon Gulf region has concluded that a rich diversity of corals managed to survive, although they were different in composition to the corals under more benign conditions.
“Of course, sea levels then were falling – and today they are rising. But if we want to know how corals cope with hostile conditions, then we have to study what happens under all circumstances,” explains Professor John Pandolfi of the ARC Centre of Excellence for Coral Reef Studies and The University of Queensland. “We’ve seen what happens to corals in the past when sea levels rose and conditions were favourable to coral growth: we wanted to see what happened when they fell and conditions were adverse.”
“When sea levels drop you get a catastrophic reduction in coral habitat and a loss of connectivity between reefs. Well, those circumstances are in some respects similar to what corals are experiencing today due to human impacts – so there are useful parallels.”
“Although it is little asked, the question of where reef species go when faced with extreme environmental situations is highly relevant for understanding their prospects of survival in the future – and what we need to do to give them the best chance,” Prof. Pandolfi suggests.
In the Huon region, the team found, coral reefs survived the hard times low of sea levels with as much richness of species – but with a different composition to what they had during the good times. “As a rule the coral colonies during the period of low sea levels were lower and slower-growing in comparison with times of high sea levels.”
In other words, Dr Pandolfi says, today’s rising sea levels – provided they do not rise too fast and ‘drown’ the reefs – offer what would otherwise be ideal growing conditions for corals, were it not for all the other human impacts, such as polluted runoff and sediment from the land, overfishing, coral bleaching and ocean acidification.
“We somehow have to find ways of preventing or offsetting each of these impacts if we expect our reefs to ride out the major climatic changes of the 20th century in as good condition as they have in the past.”
Prof. Pandolfi says the submerged fossil reefs in the Huon Gulf region provide greater confidence that coral reefs will not be wiped out worldwide by climate change – as some researchers fear – provided other impacts can be kept in check.
Their paper “Community dynamics of Pleistocene coral reefs during alternative climatic regimes”, by Danika Tager, Jody M. Webster, Don Potts, Willem Renema, Juan C. Braga and John M. Pandolfi appears in the latest issue of Ecology.
Professor John Pandolfi, COECRS and UQ, +61 7 3365 3050 or +61 0400 982 301.
Jenny Lappin, CoECRS, +61 7 4781 4222
Jan King, UQ Communications Manager, +61 7 3365 1120