High summer temperatures amplify functional differences between coral- and algae-dominated reef communities.

Area of Science:

• Marine Ecology
• Coral Reef Ecology
• Ecosystem Functioning

Background:

• Coral reefs face increasing shifts to algal dominance from anthropogenic disturbances.
• Consequences for ecosystem functions like productivity and calcification under changing conditions are unclear.

Purpose of the Study:

• To compare ecosystem functions of coral- and algae-dominated communities.
• To assess the impact of seasonal changes and temperature on these functions.

Main Methods:

• Novel in situ incubation approach used bimonthly over one year in the Red Sea.
• Quantified in situ gross and net community primary productivity, calcification, and carbon fluxes.
• Calculated activation energies to determine thermal sensitivity.

Main Results:

• Coral-dominated communities had 30% lower net productivity and 10x higher calcification than algae-dominated ones.
• Coral communities showed higher thermal sensitivity, with significant reductions in productivity and calcification with increased temperature.
• Algae-dominated communities doubled net productivity in summer, unaffected by temperature.

Conclusions:

• Coral-algal phase shifts significantly alter reef community functioning.
• Algae-dominated communities may outcompete coral communities due to higher productivity and carbon retention.
• Ocean warming amplifies these functional differences, increasing coral reef vulnerability.