Coral Skeletal Cores as Windows Into Past Symbiodiniaceae Community Dynamics

Area of Science:

• Marine Biology
• Paleoclimatology
• Genomics

Background:

• Coral reefs depend on symbiosis with Symbiodiniaceae algae for energy and structure.
• Loss of Symbiodiniaceae (coral bleaching) can cause mass mortality.
• Symbiodiniaceae communities are dynamic and shift with environmental stressors over coral lifespans.

Purpose of the Study:

• To develop and assess an approach for reconstructing Symbiodiniaceae communities from coral skeletons on decadal to centennial scales.
• To investigate how Symbiodiniaceae community dynamics vary across different coral species and locations.
• To explore the influence of environmental history, including heat stress, on Symbiodiniaceae communities.

Main Methods:

• Utilized dated coral skeleton cores from *Porites lobata* and *Diploastrea heliopora* sampled in Palau and Papua New Guinea.
• Tested various DNA extraction protocols to optimize the retrieval of skeletal-bound Symbiodiniaceae DNA.
• Employed molecular techniques to reconstruct Symbiodiniaceae communities from the coral skeletons.

Main Results:

• Reconstructed Symbiodiniaceae communities varied significantly across coral cores and DNA extraction methods.
• Decalcification-based DNA extraction protocols improved the recovery of skeletal-bound DNA.
• Distinct Symbiodiniaceae community dynamics were observed, linked to specific coral hosts and sampling locations.
• Coral cores from Palau showed associations between Symbiodiniaceae dynamics and past heat stress events.

Conclusions:

• Coral skeletons are viable archives for reconstructing past Symbiodiniaceae communities.
• This method reveals temporal and spatial variability in Symbiodiniaceae, influenced by host species and environment.
• Findings enhance paleobiological proxies for climate studies and offer insights into coral adaptation pathways.