Coral reefs persist in a balance between reef construction and reef breakdown. As corals grow, they construct the complex calcium carbonate framework that provides habitat for fish and other reef organisms.
Simultaneously, bioeroders, such as parrotfish and boring marine worms, breakdown the reef structure into rubble and the sand that nourishes our beaches. For reefs to persist, rates of reef construction must exceed reef breakdown.
This is an image of µCT scan showing the outside (top) and inside (bottom) of an experimental coral block after a one-year deployment in Kāne'ohe Bay, Hawai'i. Note the bioerosion scars inside the block.
Credit: Nyssa Silbiger at UH Mānoa and Mark Riccio at the Cornell Unversity µCT Facility for Imaging and Preclinical Research
This balance is threatened by increasing atmospheric carbon dioxide, which causes ocean acidification (decreasing ocean pH). Prior research has largely focused on the negative impacts of ocean acidification on reef growth, but new research this week from scientists at the Hawai'i Institute of Marine Biology (HIMB), based at the University of Hawai'i - Mānoa (UHM), demonstrates that lower ocean pH also enhances reef breakdown: a double-whammy for coral reefs in a changing climate.
To measure bioerosion, researchers deployed small blocks of calcium carbonate (dead coral skeleton) onto the reef for one year. Traditionally, these blocks are weighed before and after deployment on the reef; however, HIMB scientists used microCT (a high-resolution CT scan) to create before and after 3-D images of each block. According to Nyssa Silbiger, lead author of the study and doctoral candidate at HIMB, this novel technique provides a more accurate measurement of accretion and erosion rates.
The researchers placed the bioerosion blocks along a 100-ft transect on shallow coral reef in Kāne'ohe Bay, Hawai'i, taking advantage of natural variability of pH in coastal reefs. The study compared the influence of pH, resource availability, temperature, distance from shore, and depth on accretion-erosion balance. Among all measured variables, pH was the strongest predictor of accretion-erosion. Reefs shifted towards higher rates of erosion in more acidic water - a condition that will become increasingly common over the next century of climate change.
This study also highlights the impact of fine-scale variation in coastal ocean chemistry on coral reefs. Current models from the International Panel on Climate Change (IPCC) predict changes in pH for the open ocean, but these predictions are problematic for coral reefs, which are embedded in highly variable coastal ecosystems. The study found dramatic differences in ocean pH and in the daily variability of pH across a short distance.
"It was surprising to discover that small-scale changes in the environment can influence ecosystem-level reef processes," said Silbiger. "We saw changes in pH on the order of meters and those small pH changes drove the patterns in reef accretion-erosion."
Silbiger and colleagues are learning all they can from the microCT scans, as this is the first time before-and-after microCT scans were used as a measure of accretion-erosion on coral reefs. In ongoing work, they are using this technology to distinguish between accretion and erosion and to single out erosion scars from specific bioeroder groups (e.g., holes from boring worms versus bioeroding sponges). The researchers are also using this technology to investigate the drivers of the accretion-erosion balance over the much larger area of the Hawaiian Archipelago.
NJ Silbiger, O Guadoyal, FIM Thomas, MJ Donahue (2014) Reefs shift from net accretion to net erosion along a natural environmental gradient. Marine Ecology Progress Series, vol. 515, doi: 10.3354/meps10999
The School of Ocean and Earth Science and Technology at the University of Hawaii at Manoa was established by the Board of Regents of the University of Hawai'i in 1988 in recognition of the need to realign and further strengthen the excellent education and research resources available within the University. SOEST brings together four academic departments, three research institutes, several federal cooperative programs, and support facilities of the highest quality in the nation to meet challenges in the ocean, earth and planetary sciences and technologies.
Marcie Grabowski | EurekAlert!
Safeguarding sustainability through forest certification mapping
27.06.2017 | International Institute for Applied Systems Analysis (IIASA)
Dune ecosystem modelling
26.06.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau
Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.
For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...
What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.
To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...
The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....
A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...
Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision
Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...
21.07.2017 | Event News
19.07.2017 | Event News
12.07.2017 | Event News
21.07.2017 | Earth Sciences
21.07.2017 | Power and Electrical Engineering
21.07.2017 | Physics and Astronomy