Photo of the Week: Coral Turfed Out

Turf algae coats the surface of a coral reef section near Moorea, French Polynesia in what could be a common look by century’s end. Marine ecologist Maggie Johnson, a recent PhD graduate from Scripps Institution of Oceanography at the University of California San Diego and colleagues describe what happened when they grew turf algae from the South Pacific Ocean island under ocean conditions predicted for the year 2100 in a new study published in the journal Coral Reefs.

The team monitored how increasing temperature and decreasing ocean pH influence the rates of growth and photosynthesis of turf algae, which are key biological processes for sustaining coral reef ecosystem function. It found that turf algae responded positively to increasing temperatures, and to decreasing pH associated with higher CO₂ concentrations, but that these effects weren’t independent: the impact of the increased CO₂ concentrations on increased photosynthesis was higher at warmer temperatures.

“We are finding that higher levels of CO₂ can have negative effects on some sensitive marine organisms, like corals, but have positive effects on others, like seaweeds and turfs, that can take advantage of the extra CO₂ for photosynthesis,” Johnson said. “The different magnitude of response by these key competing groups on coral reefs may mean that coral reefs of the near future will look and function very differently from thriving and healthy coral-dominated reefs.”

These findings have important implications for the future of coral reefs, and indicate that some species, including turf algae can respond positively to warming temperatures and decreasing pH—but that this will come at the expense of other key reef-building species.

Scripps marine ecologist Jennifer Smith was a co-author of this study. The research was funded by the National Science Foundation, the Scripps Family Foundation and the Bohn Family.

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