Rising Prevalence of Efficient but Weaker Corals

By Kurtis Chien-Young

The El Nino events between 2015 and 2016 contributed to the destruction of much of Australia’s coral reefs. After the storms, it was estimated that around 50% of the corals were no longer functioning.

Corals have a symbiotic relationship with microscopic algae. Algae, which resides in the coral, captures light and performs photosynthesis to supply the corals with the nutrients required to build calcium carbonate foundations. With rising sea temperatures, this algae metabolism process has been escalated to the point that toxic byproducts are created, driving the algae away from the coral. Without algae, coral can only produce 5-15% of the energy it could normally have access to. The loss of algae-produced energy is called coral bleaching, and it is fatal to the coral.

However, a certain category of corals, called gorgonians, have thrived in the sudden absence of competition. Unlike other corals, gorgonians exhibit fan- or plume-like morphologies. These wide structures allow gorgonians to harvest nutrients in the absence of algae, so they can survive even as the coral reefs experience bleaching.

While gorgonians represent some hope for the reefs, they also come with downsides. Gorgonians are more flexible, but they also store less carbon to invest in rigid structures. Typically, coral reefs absorb 99% of the energy from hurricanes before the hurricanes reach the shore. However, the weaker gorgonians are less resistant to hurricanes, and their rising prevalence may have implications on the magnitudes of future tropical storm damage.

Universitat Autonoma de Barcelona. "Climate change modifies the composition of reefs." ScienceDaily. ScienceDaily, 20 September 2018. <www.sciencedaily.com/releases/2018/09/180920101110.htm>.