The reality, use and potential for cryopreservation of coral reefs

The ART of bringing extinction to a freeze - History and future of species conservation, exemplified by rhinos

The ongoing mass extinction of animal species at an unprecedented rate is largely caused by human activities. Progressive habitat destruction and fragmentation is resulting in accelerated loss of biodiversity on a global scale. Over decades, captive breeding programs of non-domestic species were characterized by efforts to optimize species-specific husbandry, to increase studbook-based animal exchange, and to improve enclosure designs. To counter the ongoing dramatic loss of biodiversity, new approaches are warranted. Recently, new ideas, particularly the application of assisted reproduction technologies (ART), have been incorporated into classical zoo breeding programs. These technologies include semen and oocyte collection, artificial insemination, and in-vitro embryo generation. More futuristic ideas of advanced ART (aART) implement recent advances in biotechnology and stem-cell related approaches such as cloning, inner cell mass transfer (ICM), and the stem-cell-associated techniques (SCAT) for the generation of gametes and ultimately embryos of highly endangered species, such as the northern white rhinoceros (Ceratotherium simum cottoni) of which only two female individuals are left. Both, ART and aART greatly depend on and benefit from the rapidly evolving cryopreservation techniques and biobanking not only of genetic, but also of viable cellular materials suitable for the generation of induced pluripotent stem cells (iPSC). The availability of cryopreserved materials bridges gaps in time and space, thereby optimizing the available genetic variability and enhancing the chance to restore viable populations.

Producing Coral Offspring with Cryopreserved Sperm: A Tool for Coral Reef Restoration

Cryopreservation is an important conservation tool, which may help reef-building coral survive. However, scaling-up from small, laboratory-sized experiments to higher-throughput restoration is a major challenge. To be an effective restoration tool, the cryopreservation methods and husbandry to produce new offspring must be defined. This study examined small and larger-scale in vitro reproduction and settlement for Acropora tenuis and Acropora millepora and found that: 1) cryopreservation of coral sperm reduced sperm motility and fertilization success in half, thus fresh sperm, capable of becoming highly motile, is key; 2) the sperm-to-egg ratio and the concentration of the cryoprotectant treatments affected fertilization success in small- and larger-scale reproduction trials using cryopreserved sperm (p < 0.05); 3) cryopreservation did not affect settlement success, as larvae produced with fresh or cryopreserved sperm had the same settlement success (p > 0.05); and 4) the residence time of the sperm within the bank was not important as the fertilization success of sperm frozen for less than 1 month was similar to that frozen up to 2 years (p > 0.05). These results described the first settlement for coral larvae produced from cryopreserved sperm and established important ground-work principles for the use of cryopreserved coral sperm for future reef restoration efforts.

Biobanking efforts and new advances in male fertility preservation for rare and endangered species

Understanding and sustaining biodiversity is a multi-disciplinary science that benefits highly from the creation of organized and accessible collections of biomaterials (Genome Resource Banks). Large cryo-collections are invaluable tools for understanding, cataloging, and protecting the genetic diversity of the world's unique animals and plants. Specifically, the systematic collection and preservation of semen from rare species has been developed significantly in recent decades with some biobanks now being actively used for endangered species management and propagation (including the introduction of species such as the black-footed ferret and the giant panda). Innovations emerging from the growing field of male fertility preservation for humans, livestock species, and laboratory animals are also becoming relevant to the protection and the propagation of valuable domestic and wild species. These new approaches extend beyond the “classical” methods associated with sperm freezing to include testicular tissue preservation combined with xenografting or in vitro culture, all of which have potential for rescuing vast amounts of unused germplasm. There also are other options under development that are predicted to have a high impact within the next decade (stem cell technologies, bio-stabilization of sperm cells at ambient temperatures, and the use of genomics tools). However, biobanking efforts and new fertility preservation strategies have to expand the way beyond mammalian species, which will offer knowledge and tools to better manage species that serve as valuable biomedical models or require assistance to reverse endangerment.

Impacts of low temperature preservation on mitochondrial DNA copy number in oocytes of the hard coral Echinopora sp

Given the current threats to coral reefs worldwide, there is an urgent need to develop protocols for the cryopreservation of reef-building corals. However, chilling may alter coral mitochondrial distribution and membrane potential, resulting in reduced ATP production. The aim of this study was to investigate the impacts of chilling on mitochondrial DNA copy number (CN) in oocytes of the hard coral Echinopora sp. Oocytes were exposed to 0.5 M, 1 M or 2 M methanol at 5, 0 or -5 °C for 2, 4, 8 and 16 h. When oocytes were chilled with no cryoprotectant (CPT) or 1 M methanol at 5 or 0 °C, the mtDNA CNs initially increased at hour 2 of incubation, although it decreased significantly over the 16 h of incubation in chilled oocytes at -5 °C. The mtDNA CN increased and picked in 0.5 M methanol at 5 °C and 0 °C at hour 8 of incubation in chilled oocytes indicating that the high mtDNA CN of these oocytes is probably responsible for withstanding high chilling sensitivity. We currently propose that 0.5 M methanol is the optimal CPT for oocytes of Echinopora sp., and potentially other reef corals.