Could some coral reefs become sponge reefs as our climate changes?

Area of Science:

• Marine Biology
• Paleontology
• Climate Change Science

Background:

• Coral reefs globally are degrading due to climate change and ocean acidification (OA).
• Past mass extinctions, like the end-Triassic, saw declines in calcifying organisms and subsequent proliferation of sponges.
• Modern coral reefs exhibit phase shifts, suggesting potential ecosystem restructuring.

Purpose of the Study:

• To hypothesize that coral reefs may transition to sponge-dominated systems.
• To investigate the potential for sponges to benefit from projected climate change and OA scenarios.
• To explore the implications of increased sponge abundance for reef functioning.

Main Methods:

• Review of the geological record for evidence of past sponge reefs.
• Analysis of reported shifts from coral- to sponge-dominated ecosystems.
• Examination of sponge holobiont responses to temperature and pH changes.

Main Results:

• Sponge reefs have a significant presence in the geological record.
• Evidence suggests shifts from coral to sponge dominance have occurred previously.
• Sponges and their symbionts exhibit varied responses to changing ocean chemistry and temperature.

Conclusions:

• Sponges are a potential beneficiary group under future climate change and OA.
• A shift towards sponge-dominated reefs is a plausible future trajectory for some current coral reef ecosystems.
• Increased sponge abundance will significantly alter overall reef functioning.