Scientists have been misled by seaweed regarding the health of reefs.

For decades, scientists have looked at seaweed as an indicator of the health of the coral reefs beneath.

But what if seaweed is misleading them?

New research at the University of British Columbia reveals that it was, 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, coverage of macroalgae is highly dependent on which species grow in a particular area. Sargassum is unlikely to grow in water polluted by agricultural runoff, but Halimida will thrive. Either way, the coral reefs will suffer.

The global research team concluded that using macroalgae coverage as an indicator of local human impacts could actually obscure the extent of damage our actions are doing to coral reefs, and cause scientists to err in identifying corals most in need of intervention.