Checking the health of coral reefs one tile at a time

Marine scientist Maggie Johnson (pictured) implements a method to measure the formation of calcium carbonate in coral reefs, which is an indicator of the health of coral reefs. Credit: KAUST; Sean Mattson

A scheme to measure calcium carbonate at the bottom of the ocean can help sea scientists monitor the health of coral reefs around the world.

Climate change and pollution from human activities are irreversibly changing many marine habitats, especially coral reefs. To assess and mitigate future impacts, ecologists need to understand how these ecosystems are functioning right now.

One indicator of the health of coral reefs is how much calcium carbonate is produced over time as the shells and skeletons of marine animals accumulate on the ocean floor. Explorers often use special tiles on the seafloor, which are slowly becoming home to pioneer plants and animals. After a year, the researchers remove the tiles to see how much calcium carbonate has accumulated on them and what living creatures are present.

“To understand how marine ecosystems change over space and time, we need to be able to compare data collected from different habitats,” says marine scientist Maggie Johnson. “But researchers use a range of approaches or measure different variables, which means the data may not be directly comparable,” she adds. This makes it difficult to build a global picture of the health of the marine ecosystem.

Credit: King Abdullah University of Science and Technology

Johnson and colleagues developed a standardized method for making and deploying calcification accretion units (CAUs), which are similar to subsidence tiles but are more specifically used to measure calcium carbonate. The detailed guide provides detailed instructions on how to make tiles and assemble CAUs, from material suppliers to measurements, and how to place and retrieve them, allowing researchers to collect comparable data on coral and oyster reefs around the world. .

“Coral reefs cover less than one percent of the seafloor, but provide more than 25 percent of the ocean’s biodiversity,” says Johnson. “Most of this diversity comes from tiny critters that live in invisible cracks and crevices,” she adds. These hidden species, or “cryptic taxa”, cannot be captured by visual surveys, but there is little space in CAU for these tiny taxa to occupy. “During collection, the tiles must be placed in ziplock bags to keep the community of mystery creatures intact all the way to the lab,” says Johnson.

Guide published in Methods of ecology and evolutionadvises processing samples immediately while animals and plants are still alive. This includes taking high resolution photographs, which are later used for species discovery and microscope observations to count young corals. The calcium carbonate is then removed with a weak acid.

“By weighing the tiles before and after they are decalcified, the researchers can calculate how much calcium carbonate is deposited on the tiles in a year,” says Johnson. “This figure can help compare the health of reefs in different parts of the world, or how the health of one reef changes over time.”

Understanding the impact of human activities on marine habitats will help researchers and governments find ways to mitigate negative impacts. “This standardized and accessible approach will encourage collaboration and informed decision making, even when using data from around the world,” Johnson concludes.

Coasts are sinking, coral reefs are eroding due to warming and acidification

Additional Information:
Maggie D. Johnson et al., Calcification Augmentation Units (CAU): A standardized approach to quantifying calcium carbonate recruitment and buildup in marine habitats, Methods of ecology and evolution (2022). DOI: 10.1111/2041-210X.13867

Courtesy of King Abdullah University of Science and Technology.

Quote: Checking Coral Reef Health One Tile at a Time (2022 June 15), retrieved June 15, 2022 from

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