Biobanks provide vital support to a diverse range of research including biomedical, agricultural and conservation research. A recent study published in Scientific Reports shows how biobanks can help tackle the billion dollar problem of coral bleaching.
Biobanks Safeguard Against Coral Loss
Coral reefs are an essential part of our oceans, housing more than 2 million species. Reefs are also economic powerhouses, generating around US$30 billion a year in goods and services, including medicines, fishing and tourism (1). Unfortunately coral reefs are under threat due to ocean warming.
Corals owe their bright colors to symbiotic algae that live inside their tissues and provide nutrients. If ocean temperatures are too high, the algae die and the corals lose their colors, a process known as coral bleaching. Bleached corals are more susceptible to disease and can die from starvation (1). The Great Barrier Reef in Australia, the largest coral reef in the world, has lost half of its coral from bleaching due to high sea temperatures.
Experts agree that new research is needed to help coral adapt to environmental changes and stresses. We also need a way to preserve genetic material from marine species in case there is a massive extinction event due to coral reef damage. Biobanks offer a way to safely store genetic material for long periods of time.
Storing Coral Larvae in Biobanks
Scientists have previously frozen and thawed coral sperm, and used this biobanked sperm to successfully fertilize coral (2). However, many coral colonies only release eggs once a year. This makes it difficult to fertilize wild colonies with sperm from biobanks. In the wild, coral sperm and eggs join to form free-swimming larvae that settle to become adult polyps. Therefore, scientists proposed that it might be a better conservation approach to biobank coral embryos or larvae and use these to repopulate damaged reefs.
Biobanks have cryopreserved sperm, oocytes and embryos from humans and many other mammals, including farm animals, research animals and endangered species (3). However, it is much harder to biobank embryos and larvae from corals, and other non-mammalian species, because their cell membranes are not as permeable to water and cryoprotectant solutions.
Ultra-Fast Freezing and Thawing
Cryoprotectant solutions and vitrification, or ultra-fast freezing, can help prevent cell damage and death due to ice crystal formation. Ice crystals can form inside cells during the freezing and thawing process, and cause structural damage and cell death. Researchers recently used vitrification to successfully freeze and thaw coral larvae (2). Standard vitrification methods use very high concentrations of cryoprotectants to protect cells during flash freezing and thawing. However, this didn’t work for coral larvae, as high concentrations of cryoprotectants killed the larvae.
After trialing several different cryoprotectant solutions, the researchers found success with a solution containing propylene glycol, dimethyl sulfoxide (DMSO), trehalose and gold nanoparticles. Standard cryopreservation methods often use ultra-fast freezing but slow controlled-rate thawing. In contrast, in this study, researchers performed both ultra-fast freezing and ultra-fast thawing to prevent ice crystals forming inside the coral larvae. They thawed the larvae with an infrared laser at an estimated rate of around 4,500,000°C/min. This was done to offset the lower cryoprotectant solution levels tolerated by the coral larvae.
The researchers had most success freezing and thawing 2-day old larvae – 43% of this group survived, swam and continued to develop post-thawing.
Conclusions
This research shows that it is possible to store coral larvae in biobanks. However, the authors did not report releasing frozen-thawed larvae into the wild. Therefore, it is not clear whether these larvae would be able to settle, form into polyps and rebuild reefs. With more work, this approach may be successful in coral and other marine animals and could allow scientists to biobank embryos or larvae from many different species.
References
- Ocean Find Your Blue. Corals and Coral Reefs (Online) Accessed November 19, 2018.
- Daly et al. Successful cryopreservation of coral larvae using vitrification and laser warming. Scientific Reports. 2018.
- Mandawala et al. Cryopreservation of animal oocytes and embryos: current progress and future prospects. Theriogenology. 2016.
