Environmental Records from Great Barrier Reef Corals: Inshore versus Offshore Drivers

• Published in: PloS one Vol. 8; no. 10; p. e77091
• Main Authors: Walther, Benjamin D., Kingsford, Michael J., McCulloch, Malcolm T.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 18.10.2013; Public Library of Science (PLoS)
• Subjects: Animals; Annual variations; Anthozoa - chemistry; Anthozoa - physiology; Australia; Barium - metabolism; Calcium - metabolism; Carbonates; Catchments; Climate change; Cold water; Continental shelves; Coral reef ecosystems; Coral Reefs; Corals; Depth indicators; Earth; Earth science; Ecological monitoring; Ecosystem; El Nino-Southern Oscillation; Environment; Environmental changes; Environmental conditions; Environmental monitoring; Environmental Monitoring - methods; Environmental quality; Erosion; Flooding; Floods; Fluctuations; Geochemistry; Geography; Interannual variability; Monsoons; Nutrients; Oceanographic conditions; Oceanography; Offshore; Offshore engineering; Offshore structures; Precipitation; Protection and preservation; Rain; Recorders; Reefs; Salinity; Seasons; Seawater - chemistry; Sedimentation & deposition; Temperature; Temporal variations; Terrigenous sediments; Trace elements; Upwelling; Variation; Water monitoring; Water temperature; Wavelet Analysis; Australia; Western Australia Australia; Canberra Australian Capital Territory Australia; Australian Capital Territory Australia
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0077091

The biogenic structures of stationary organisms can be effective recorders of environmental fluctuations. These proxy records of environmental change are preserved as geochemical signals in the carbonate skeletons of scleractinian corals and are useful for reconstructions of temporal and spatial fluctuations in the physical and chemical environments of coral reef ecosystems, including The Great Barrier Reef (GBR). We compared multi-year monitoring of water temperature and dissolved elements with analyses of chemical proxies recorded in Porites coral skeletons to identify the divergent mechanisms driving environmental variation at inshore versus offshore reefs. At inshore reefs, water Ba/Ca increased with the onset of monsoonal rains each year, indicating a dominant control of flooding on inshore ambient chemistry. Inshore multi-decadal records of coral Ba/Ca were also highly periodic in response to flood-driven pulses of terrigenous material. In contrast, an offshore reef at the edge of the continental shelf was subject to annual upwelling of waters that were presumed to be richer in Ba during summer months. Regular pulses of deep cold water were delivered to the reef as indicated by in situ temperature loggers and coral Ba/Ca. Our results indicate that although much of the GBR is subject to periodic environmental fluctuations, the mechanisms driving variation depend on proximity to the coast. Inshore reefs are primarily influenced by variable freshwater delivery and terrigenous erosion of catchments, while offshore reefs are dominated by seasonal and inter-annual variations in oceanographic conditions that influence the propensity for upwelling. The careful choice of sites can help distinguish between the various factors that promote Ba uptake in corals and therefore increase the utility of corals as monitors of spatial and temporal variation in environmental conditions.