How seaweed has been misleading scientists about reef health

Newswise —

For years, researchers have relied on seaweed to gauge the well-being of coral reefs below.

But could the seaweed be deceiving them?

Recently published findings from UBC expose that the previous method of using seaweed as a signal for coral reef health is inaccurate, leaving scientists to search for alternative approaches to determine if human activities are detrimental to a specific reef.

According to Dr. Sara Cannon, the study's lead author and a postdoctoral fellow at the UBC Institute for the Oceans and Fisheries, this is particularly crucial now, with the increasing global threat of climate-related pressures on reefs.

Local species behave differently

Macroalgae, a type of organism that includes seaweed, has been traditionally utilized as a substitute for coral reef health. Macroalgae present at the ocean's surface has been deemed an ideal indicator due to its ease and speed of measurement. Since the 1970s, researchers have operated under the belief that local human activities promote macroalgae growth, resulting in harm to underlying reefs.

A recent study published in Global Change Biology analyzed data from more than 1,200 locations in the Indian and Pacific Oceans spanning 16 years. The results of the study indicated that the approach of using macroalgae as an indicator of coral reef health is inaccurate and potentially conceals signs of stress in the reef ecosystem.

The study found that macroalgae coverage is highly dependent on the species present in a given area. For instance, Sargassum is less likely to grow in water contaminated by agricultural runoff, while Halimeda will flourish in such conditions. In either case, the health of the reef ecosystem may be negatively impacted. Therefore, the use of macroalgae coverage as a proxy for reef health may not accurately reflect the actual state of the reef, and alternative approaches are required to assess human impacts on coral reefs.

The international research team reached the conclusion that employing macroalgae coverage as an indicator of human impacts can obscure the degree to which our actions are damaging reefs, causing researchers to incorrectly identify reefs in dire need of intervention. In essence, the use of macroalgae as a measure of reef health may provide a false sense of security and cause scientists to overlook critical signs of reef stress. Consequently, new and more reliable methods for assessing reef health are required to address the growing global threat to coral reefs.