Banking coral larvae at scale with cryomesh: opportunities and challenges

Coral populations around the world are threatened by human activity and warming oceans. Novel and scalable approaches to cryopreserve coral germplasm, algal symbionts, and adult tissues can improve access to banked material for biological research and reef restoration efforts, thus supporting biodiversity and increasing population resilience to climate change. We recently vitrified and rewarmed larvae of the solitary Hawaiian stony coral species Lobactis scutaria (mushroom coral) with one-step loading of a 3.5-M multi-component cryoprotective agent (CPA) solution, removal of excess CPA, liquid nitrogen plunge cooling, warming on a novel cryomesh substrate, and two-step CPA unloading. With optimization of substrate geometry and experimental methods, estimated cooling rate within the larvae was 9.4 × 104 °C/min, warming rate was 1.2 × 105 °C/min, and post-thaw larval recovery reached 85%. This result improves on prior vitrification work with the same species using 1-μL droplet plunge cooling of the same CPA solution on a plastic film followed by nanoparticle-mediated infrared laser pulse warming (plunge cooling rate < 6.9 × 104 °C/min, laser warming 4.5 × 106 °C/min, 43% recovery). Here we present our cryomesh results, propose technical directions and collaborative efforts that will allow deployment of this and related technologies at a scale that will support research and restoration activities, and describe the remaining challenges in cryopreservation of larvae of a wider range of coral species.