New Study Out Published October 2023

Coral reefs across the globe are facing degradation owing to climate change impacts like ocean warming. A crucial aspect of restoring these reefs is the successful settlement of coral larvae on reef surfaces. However, there’s been a decline in larval settlement, and enhancing this process in aquaculture conditions is vital for reef restoration. This study delved into understanding the role of microbes in the larval settlement of the coral species Acropora tenuis.

Microbial Biofilm Investigation

Larvae were subjected to biofilms that were cultivated on concrete blocks both at a reef and in aquaria. Post-settlement, a DNA sequencing analysis was conducted on the biofilm microbes. The analysis revealed highly structured microbial communities associated with different levels of larval settlement.

• Diverse microbial species were linked to higher settlement, pinpointing to species like Myxococcales and Granulosicoccus as potential settlement inducers.
• Pseudovibrio denitrificans was identified, a microbe known for inducing coral larval settlement.
• On the flip side, some microbes like Reichenbachiella agariperforans were associated with lower settlement.

Biofilm Transition

As biofilms aged, a transition was observed in the microbial community. Initial colonizers were followed by secondary colonizers which possibly transition biofilms to allow settlement inducers to establish. Bridging microbes like Thiohalorhabdaceae species were found to connect mixed and high settlement communities, creating conducive microenvironments for larval settlement.

Eukaryotic Inhabitants

Notably, crustose coralline algae (CCA) were abundant in high settlement biofilms, along with other diverse eukaryotes, not just CCA. Brown algae and diatoms, on the other hand, dominated low settlement communities, hinting at a possible inhibitory effect on larvae of some species.

Aquarium Vs. Reef Biofilm Conditioning

Aspect	Aquarium	Reef
Advantages	– Identified settlement inducing microbes	– Natural environment mimicking real reef conditions
	– Controlled environment for standardized conditioning	– Uncovered natural settlement inducers like Pseudovibrio denitrificans
Disadvantages	– Microbial differences from reef biofilms	– Less control leading to more variability
		– Challenging ocean access for research and aquaculture

Concluding Insights

The study sheds light on the distinct and diverse microbial communities associated with varying coral larval settlement levels. It underscores the potential of certain microbes as settlement inducers and inhibitors. A balanced approach utilizing both aquarium and reef environments for biofilm conditioning could be pivotal. The controlled conditions in an aquarium can expedite the discovery process, while the natural reef environment is critical for validating these findings. This dual-approach could significantly contribute to optimizing biofilm sources, thereby maximizing coral larval settlement success, a step forward towards effective reef restoration amidst changing climate conditions.

For further insights into coral ecosystems and restoration, explore how corals manage in nutrient-scarce waters, the methods of coral gardening and fragmentation, the intricacies of sexual coral reproduction, the potential of Biorock Electro-Accretion, the feasibility of coral growth on concrete, and a simplified explanation of coral bleaching.

Original article

Turnlund, A. C., Vanwonterghem, I., Botté, E. S., Randall, C. J., Giuliano, C., Kam, L., Bell, S., O’Brien, P., Negri, A. P., Webster, N. S., & Lurgi, M. (2023). Linking differences in microbial network structure with changes in coral larval settlement. ISME Communications, 3, 114. https://doi.org/10.1038/s43705-023-00320-x