The study presents a comprehensive analysis of the effects of high and low pCO2 (ocean acidification) on coral reef ecosystems in the Milne Bay region of Papua New Guinea. The data suggests that tropical coral reefs can still exist at a seawater pH of 7.8 (750 ppm pCO2), but with significant losses in biodiversity, structural complexity, and resilience. As pH declines from 8.1 to 7.8, the reef community shifts from fast-growing, structurally complex corals to slow-growing, structurally simple massive Porites corals, maintaining overall coral cover. Reef development ceases at a pH of 7.7 (980 ppm pCO2), suggesting this is a terminal threshold for any form of coral reef development.
The study provides in-situ measurements of various biotic responses, including coral calcification rates, tissue thickness, bioerosion, and symbiotic algae composition. Seagrass communities also showed changes in shoot density, below-ground biomass, and epiphytic cover under high pCO2 conditions. The study highlights the need for rapid transition to low CO2 emissions to minimize the risk of profound losses of coral reef ecosystem functions and services due to both climate change and ocean acidification. The rate of atmospheric CO2 increase continues to accelerate.
The study also used a Shimadzu TOC-V Analyzer for inorganic carbon measurements, calibrated with the certified reference MESS-1 and two in-house standards. Statistical methods, including Generalized additive models (GAMs) and Generalized linear models (GLMs), were used to predict pH values from field observations along 10-m sections of transects and spatial grids of the three reefs. The GLMs were also used to assess changes in biota along the pH gradient at the Upa-Upasina reef.
The study provides a detailed analysis of the effects of ocean acidification on coral reef ecosystems. It highlights the need for urgent action to reduce CO2 emissions in order to protect these critical ecosystems. The study also provides a comprehensive understanding of the various biotic responses to changes in pH, offering valuable insights for further research in this field.
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