Scientists have been misled for decades – new study reveals seaweed’s deceptive role in coral reef health

Scientists have been using seaweed as an indicator of coral reef health for decades.

But what if seaweed is misleading them?

New research from the University of British Columbia reveals that they were, and scientists need new ways to determine whether human activity is harming specific coral reefs.

“This is especially critical today, given that coral reefs globally are threatened by climate-induced stresses,” said Dr. Sarah Cannon, a postdoctoral fellow at the UBC Institute for Oceans and Fisheries and lead author of the study.

Local species behave differently

Seaweeds belong to a group of organisms called macroalgae. Macroalgae at the ocean surface have long served as a proxy for coral reef health, as they are relatively quick and easy to measure. Since the 1970s, scientists have hypothesized that local human impacts increase macroalgae while simultaneously destroying dormant coral reefs.

However, the study just published in The biology of global change It looked at data from more than 1,200 sites in the Indo-Pacific over 16 years and revealed that this approach is misleading and may contain subtle signs of coral stress.

For example, macroalgae coverage is highly dependent on[{” attribute=””>species growing in a particular area. Sargassum is less likely to grow in water contaminated by agricultural runoff, but Halimeda will thrive. In both cases, a reef will suffer.

The global research team concluded that using macroalgae coverage as an indicator of local human impacts can actually obscure how much our actions are harming reefs, and cause scientists to misidentify the reefs most in need of intervention.

Reference: “Macroalgae exhibit diverse responses to human disturbances on coral reefs” by Sara E. Cannon, Simon D. Donner, Angela Liu, Pedro C. González Espinosa, Andrew H. Baird, Julia K. Baum, Andrew G. Bauman, Maria Beger, Cassandra E. Benkwitt, Matthew J. Birt, Yannick Chancerelle, Joshua E. Cinner, Nicole L. Crane, Vianney Denis, Martial Depczynski, Nur Fadli, Douglas Fenner, Christopher J. Fulton, Yimnang Golbuu, Nicholas A. J. Graham, James Guest, Hugo B. Harrison, Jean-Paul A. Hobbs, Andrew S. Hoey, Thomas H. Holmes, Peter Houk, Fraser A. Januchowski-Hartley, Jamaluddin Jompa, Chao-Yang Kuo, Gino Valentino Limmon, Yuting V. Lin, Timothy R. McClanahan, Dominic Muenzel, Michelle J. Paddack, Serge Planes, Morgan S. Pratchett, Ben Radford, James Davis Reimer, Zoe T. Richards, Claire L. Ross, John Rulmal Jr., Brigitte Sommer, Gareth J. Williams and Shaun K. Wilson, 5 April 2023, Global Change Biology.
DOI: 10.1111/gcb.16694