Coral Skeletons Provide Historical Evidence of Phosphorus Runoff on the Great Barrier Reef

Mallela, Jennie; Lewis, Stephen E.; Croke, Barry

doi:10.1371/journal.pone.0075663

Cited by 26 publications

(12 citation statements)

References 34 publications

(42 reference statements)

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“…Excess river sediment, nutrient and pesticide loads to the GBR lagoon are derived from (i) surface and subsurface erosion, predominantly in rangeland cattle grazing settings; (ii) fertilizer applications in sugarcane and broad‐acre cropping; and (iii) pesticides (particularly photosystem II inhibiting herbicides) primarily applied during sugarcane cultivation (Kroon et al ., ). Signatures of increased river loads are observed in GBR coral cores for sediment since the 1900s (Mcculloch et al ., ; Lewis et al ., ) and for nutrients since the mid‐20th century (Jupiter et al ., ; Mallela et al ., ) and are associated with increased soil erosion and fertilizer application. Coral and sediment cores from the inshore GBR also show evidence of changes in community composition of corals (Roff et al ., ) over the last century, indicative of higher water turbidity and increased nutrient availability in the GBR lagoon.…”

Section: Status and Trends Of Gbr Water Quality And Ecosystem Conditionmentioning

confidence: 99%

Towards protecting the Great Barrier Reef from land‐based pollution

Kroon

Thorburn

Schaffelke

et al. 2016

Global Change Biology

189

111

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The Great Barrier Reef (GBR) is an iconic coral reef system extending over 2000 km along the north-east coast of Australia. Global recognition of its Outstanding Universal Value resulted in the listing of the 348 000 km 2 GBR WorldHeritage Area (WHA) by UNESCO in 1981. Despite various levels of national and international protection, the condition of GBR ecosystems has deteriorated over the past decades, with land-based pollution from the adjacent catchments being a major and ongoing cause for this decline. To reduce land-based pollution, the Australian and Queensland Governments have implemented a range of policy initiatives since 2003. Here, we evaluate the effectiveness of existing initiatives to reduce discharge of land-based pollutants into the waters of the GBR. We conclude that recent efforts in the GBR catchments to reduce land-based pollution are unlikely to be sufficient to protect the GBR ecosystems from declining water quality within the aspired time frames. To support management decisions for desired ecological outcomes for the GBR WHA, we identify potential improvements to current policies and incentives, as well as potential changes to current agricultural land use, based on overseas experiences and Australia's unique potential. The experience in the GBR may provide useful guidance for the management of other marine ecosystems, as reducing land-based pollution by better managing agricultural sources is a challenge for coastal communities around the world.

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Section: Status and Trends Of Gbr Water Quality And Ecosystem Conditionmentioning

confidence: 99%

Towards protecting the Great Barrier Reef from land‐based pollution

Kroon

Thorburn

Schaffelke

et al. 2016

Global Change Biology

189

111

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“…While environmental effects on mechanical properties are understudied (Ragazzola et al 2016;Melbourne et al 2018), it is well documented that environmental conditions can impact the geochemistry of the aragonite (Druffel 1997). For example, the relative amount of Sr and Mg incorporated into coral skeletons is related to SST (Smith et al 1979), while the absolute amount of P and Ba may be influenced by nutrient availability and sedimentation (Mallela et al 2013;LaVigne et al 2016). As a result of these relationships, long-lived corals, most commonly Porites lobata and Porites lutea, are used in paleoceanography to reconstruct past climates (Druffel 1997;LaVigne et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Environmental impact on the mechanical properties of Porites spp. corals

et al. 2021

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Despite the economic and ecological importance of corals’ skeletal structure, as well as their predicted vulnerability to future climate change, few studies have examined the skeletal mechanical properties at the nanoscale. As climate change is predicted to alter coral growth and physiology, as well as increase mechanical stress events (e.g., bioerosion, storm frequency), it is crucial to understand how skeletal mechanical properties change with environmental conditions. Moreover, while material properties are intimately linked to the chemical composition of the skeleton, no previous study has examined mechanical properties alongside carbonate geochemical composition. Using Porites coral cores from a wide range of reef environments (Thailand, Singapore, Taiwan), we correlated coral’s micro-mechanical properties with chemical composition. In contrast to previous mechanical measurements of reef-building corals, we document unprecedented variability in the hardness, stiffness, and micro-cracking stress of Porites corals across reef environments, which may significantly decrease the structural integrity of reef substrate. Corals from environments with low salinity and high sedimentation had higher organic content and fractured at lower loads, suggesting that skeletal organic content caused enhanced embrittlement. Within individual coral cores, we observed seasonal variability in skeletal stiffness, and a relationship between high sea surface temperature, increased stiffness, and high-density. Regionally, lower Sr/Ca and higher Mg/Ca coincided with decreased stiffness and hardness, which is likely driven by increased amorphous calcium carbonate and skeletal organic content. If the coral is significantly embrittled, as measured here in samples from Singapore, faster erosion is expected. A decrease in skeletal stiffness will decrease the quality of reef substrate, enhance the rate of bioerosion by predators and borers, and increase colony dislodgement, resulting in widespread loss of structural complexity.

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“…Therefore, terrestrial runoff inputs of Ba to coastal upwelling sites can compromise the interpretation of Ba/Ca as an upwelling proxy in some locations. In coastal regions affected by riverine input, skeletal Ba/Ca has been shown to track changes in riverine sediment discharge, as barium desorbs from suspended sediment in low salinity estuarine waters, increasing Ba SW and thus, skeletal Ba/Ca coral (Li and Chan, 1979;Alibert et al, 2003;McCulloch et al, 2003;Sinclair and McCulloch, 2004a;Fleitmann et al, 2007;Prouty et al, 2008;Carriquiry and Horta-Puga, 2010;Prouty et al, 2010;Horta-Puga and Carriquiry, 2012;Maina et al, 2012;Moyer et al, 2012;Mallela et al, 2013). While the previous work discussed above has correlated Ba/Ca coral variations to the occurrence of upwelling and terrestrial runoff events, the lack of a direct calibration of Ba/Ca coral against Ba SW has limited interpretations to relative changes in Ba/Ca coral rather than quantitative reconstructions of absolute Ba SW .…”

Section: Introductionmentioning

confidence: 99%

Multi-colony calibrations of coral Ba/Ca with a contemporaneous in situ seawater barium record

LaVigne

Grottoli

Palardy

et al. 2016

Geochimica et Cosmochimica Acta

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The coral skeleton barium to calcium ratio (Ba/Ca coral), a proxy for seawater barium concentrations (Ba SW) has been interpreted as a tracer of upwelling based on the characteristic "nutrient like" depth profile of Ba SW. However, in some tropical regions, such as the Gulf of Panamá, substantial influence of terrestrial runoff inputs and differences between the vertical distribution of Ba SW and that of the major nutrients (nitrate and phosphate) in the upper water column can complicate the interpretation of Ba/Ca coral as an upwelled nutrient proxy. In the Gulf of Panamá, contemporaneous Ba/Ca coral records from multiple colonies of Porites lobata, Pavona gigantea, and Pavona clavus corals record a nearly twofold change in surface water Ba SW as a 20-70% increase in skeletal Ba/Ca with excellent correlation among Ba/Ca records from co-located colonies (r=0.86-0.99). These results provide, for the first time, an absolute calibration of the coral Ba proxy with a contemporaneous Ba SW record. Compiling the Ba/Ca coral records from three co-located colonies of each species into taxon-specific composite regressions reveals strong statistically significant correlations with the Ba SW time-series record (p < 0.001). Differences among taxa in regression slope, y-intercept, and average distribution coefficient, as well as a demonstration of the application of the Pavona clavus calibration to a previously published Ba/Ca coral record, emphasize the necessity of using taxon-specific calibrations to reconstruct changes in Ba SW with accuracy. These results support the application of Ba/Ca coral to reconstruct past changes in absolute Ba SW concentrations, adding an important tool to the collection of geochemical proxies for reconstructing surface ocean biogeochemical processes in the past. 5 2. METHODS 2.1. Samples An archived set of replicate coral colonies and a time series of in situ seawater samples from a previous study in the Gulf of Panamá were analyzed to assess inter-colony Ba/Ca coral reproducibility (

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Coral Skeletons Provide Historical Evidence of Phosphorus Runoff on the Great Barrier Reef

Cited by 26 publications

References 34 publications

Towards protecting the Great Barrier Reef from land‐based pollution

Towards protecting the Great Barrier Reef from land‐based pollution

Environmental impact on the mechanical properties of Porites spp. corals

Multi-colony calibrations of coral Ba/Ca with a contemporaneous in situ seawater barium record

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