Understanding Change on the Reef: Past and Present

Dr. Tara Clark (UQ)

Researchers from NERP Project 1.3 are well on their way to uncovering many of the Great Barrier Reef’s secrets by studying fossil and dead coral remains.

Their results have documented long term changes on coral reef ecosystems spanning thousands of years, as well as more recent change that coincides with human settlement on the Queensland coastline.

Using cores taken through the reef using a percussion coring technique (put simply, aluminium tubing hammered into the reef similar to a star picket for a fence), the researchers are able to examine how coral communities have changed through time. By dating coral fragments within the cores using the highly precise uranium-series dating method, they are able to determine the timing of significant changes in community structure, storm events, as well as reef accretion rates.

So far, more than 140 reef matrix cores have been collected over the entire length of the inshore region of the Great Barrier Reef, including the far north, central and southern regions.

Cores taken through reefs in the southern Great Barrier Reef have revealed a long history of reef development for several millennia. However, close examination of the corals present in the cores suggest that at some locations there have been reef turn on/turn-off events throughout the reefs history that coincide with the rise and fall of past sea-level. At other sites, changes in coral community composition occurred several centuries ago - well before European settlement - suggesting that other non-anthropogenic factors (e.g. climate) were the major drivers of abrupt change in coral communities in the past.

More recent changes in coral community structure have been seen within cores taken from reefs adjacent to the Wet Tropics region. Preliminary evidence suggests that these changes coincide with the timing of a shift in coral community structure observed in cores taken from Pelorus Island, central Great Barrier Reef. These results imply that significant changes on inshore reef ecosystems may have occurred over a much broader spatial scale. At Pelorus Island, coral communities were found to have switched from an Acropora dominated community to that characterised by corals typical of turbid water environments between 1950-1970 AD. While the exact cause of this change is unknown, the researchers speculate that the lack of Acropora recovery is due to the chronic increase in sediment and nutrient delivery to the region since European settlement.

These case studies are just an example of the many exciting discoveries emerging from this research, and demonstrate the need to understand both long (centennial, millennial) and short-term (decadal) changes in coral reef communities, as well as local (e.g. water quality) and global scale (e.g. El Niño Southern Oscillation) drivers of change in order to appropriately assess the current state of the Great Barrier Reef as well as the effects of existing management strategies.

For more information, contact Prof. John Pandolfi (j.pandolfi@uq.edu.au), Prof. Jian-xi Zhao (j.zhao@uq.edu.au) or Dr. Tara Clark (t.clark1@uq.edu.au)