Evaluation of boron isotope ratio as a pH proxy in the deep sea coral Desmophyllum dianthus: evidence of physiological pH adjustment

The boron isotope ratio (δ¹¹B) of foraminifers and tropical corals has been proposed to record seawater pH. To test the veracity and practicality of this potential paleo-pH proxy in deep sea corals, samples of skeletal material from twelve archived modern Desmophyllum dianthus (D. dianthus) corals from a depth range of 274–1470 m in the Atlantic, Pacific, and Southern Oceans, ambient pH range 7.57–8.05, were analyzed for δ¹¹B. The δ¹¹B values for these corals, spanning a range from 23.56 to 27.88, are found to be related to seawater borate δ¹¹B by the linear regression: δ¹¹B_coral=(0.76±0.28) δ¹¹B_borate+(14.67±4.19) (1 standard error (SE)). The D. dianthus δ¹¹B values are greater than those measured in tropical corals, and suggest substantial physiological modification of pH in the calcifying space by a value that is an inverse function of seawater pH. This mechanism partially compensates for the range of ocean pH and aragonite saturation at which this species grows, enhancing aragonite precipitation and suggesting an adaptation mechanism to low pH environments in intermediate and deep waters. Consistent with the findings of Trotter et al. (2011) for tropical surface corals, the data suggest an inverse correlation between the magnitude of a biologically driven pH offset recorded in the coral skeleton, and the seawater pH, described by the equation: ΔpH=pH recorded by coral−seawater pH=−(0.75±0.12) pH_w+(6.88±0.93) (1 SE). Error analysis based on 95% confidence interval(CI) and the standard deviation of the regression residuals suggests that the uncertainty of seawater pH reconstructed from δ¹¹B_coral is ±0.07 to 0.12 pH units. This study demonstrates the applicability of δ¹¹B in D. dianthus to record ambient seawater pH and holds promise for reconstructing oceanic pH distribution and history using fossil corals.

Coral reefs of the turbid inner-shelf of the Great Barrier Reef, Australia: an environmental and geomorphic perspective on their occurrence, composition and growth

Investigations of the geomorphic and sedimentary context in which turbid zone reefs exist, both in the modern and fossil reef record, can inform key ecological debates regarding species tolerances and adaptability to elevated turbidity and sedimentation. Furthermore, these investigations can address critical geological and palaeoecological questions surrounding longer-term coral-sediment interactions and reef growth histories. Here we review current knowledge about turbid zone reefs from the inner-shelf regions of the Great Barrier Reef (GBR) in Australia to consider these issues and to evaluate reef growth in the period prior to and post European settlement. We also consider the future prospects of these reefs under reported changing water quality regimes. Turbid zone reefs on the GBR are relatively well known compared to those in other reef regions. They occur within 20 km of the mainland coast where reef development may be influenced by continual or episodic terrigenous sediment inputs, fluctuating salinities (24-36 ppt), and reduced water quality through increased nutrient and pollutant delivery from urban and agricultural runoff. Individually, and in synergy, these environmental conditions are widely viewed as unfavourable for sustained and vigorous coral reef growth, and thus these reefs are widely perceived as marginal compared to clear water reef systems. However, recent research has revealed that this view is misleading, and that in fact many turbid zone reefs in this region are resilient, exhibit relatively high live coral cover (> 30%) and have distinctive community assemblages dominated by fast growing (Acropora, Montipora) and/or sediment tolerant species (Turbinaria, Goniopora, Galaxea, Porites). Palaeoecological reconstructions based on the analysis of reef cores show that community assemblages are relatively stable at millennial timescales, and that many reefs are actively accreting (average 2-7 mm/year) where accommodation space is available, despite recent anthropogenic pressures. These turbid zone reefs challenge traditional views on the environmental conditions required for active reef growth, but given their proximity to land and associated stresses, current knowledge on these less well understood reefs should be synthesised to aid coastal management directives. Terrigenous sediments are a dominant influence on turbid zone reef occurrence, composition and growth, and, therefore, the assessment of their future prospects will require a detailed understanding of the sedimentary regimes under which they occur and of their differential response modes.

Some like it cold as sea life moves south

Ocean species that used to live off Sydney half a century ago now inhabit the Southern Ocean as climate change drives fish, plankton and microbes to colder waters, a scientific snapshot of marine health has found.

The report by 80 scientists, led by the CSIRO, documents the southward migration of marine life, as well as ocean acidification and coral bleaching that are attributable to climate change.

Full report: ocean acidification (report and video)

Increasing atmospheric CO2 concentration is causing increased absorption of CO2 by the world’s oceans, in turn driving a decline in seawater pH and changes in ocean carbonate chemistry that are collectively referred to as ocean acidification. Evidence is accumulating to suggest ocean acidification may directly or indirectly affect many marine organisms and ecosystems, some of which may also hold significant social and economic value to the Australian community.
This report card aims to provide a brief overview of the current state of scientific knowledge regarding the process of ocean acidification; current and future projected levels of ocean acidification; and, observed and projected impacts of current and future predicted levels of ocean acidification on marine organisms and ecosystems in the region. This Report Card also briefly discusses potential social and economic implications, policy challenges, and the key knowledge gaps needing to be addressed.

Marine climate change in Australia – 2012 report card

This 2012 Report Card demonstrates that climate change is having significant impacts on Australia’s oceans and marine ecosystems.

Many new changes have been documented since the 2009 Report Card. There is now striking evidence of extensive southward movements of tropical fish and plankton species in southeast Australia, declines in abundance of temperate species, and the first signs of the effect of ocean acidification on marine species with shells.