Coral larvae conservation: Physiology and reproduction

Cryophysiology of coral microfragments: effects of chilling and cryoprotectant toxicity

Coral reefs are being degraded at alarming rates and decisive intervention actions are urgently needed. One such intervention is coral cryopreservation. Although the cryopreservation of coral sperm and larvae has been achieved, preservation of coral fragments including both its tissue and skeleton, has not. The overarching aim of this study was to understand and assess the physiological stressors that might underlie coral fragment cryopreservation, understand the long-term consequences of these exposures to continued growth, and develop a health metrics scale for future research. Therefore, we assessed small fragments (~1 cm2) from the Hawaiian coral, Porites compressa, examining: (1) chill sensitivity; (2) chemical sensitivity to complex cryoprotectants; (3) methods to safely remove algal symbionts of coral for cryopreservation; (4) continued growth over time of coral fragments exposed to chilling and cryoprotectants; and (5) assessment of health and viability of coral fragments post the applied treatments. Corals were able to withstand chilling to 0 °C for 1 min and after 2 weeks were not significantly different from the live controls, whereas, corals exposed to complex cryoprotectants needed 3 weeks of recovery. Most importantly, it appears that once the coral fragments had surpassed this initial recovery, there was no difference in subsequent growth. Technological advances in cryo-technology promise to support successful coral fragment cryopreservation soon, and its success could help secure much of the genetic and biodiversity of reefs in the next decade.

Cryopreservation and revival of Hawaiian stony corals using isochoric vitrification

Corals are under siege by both local and global threats, creating a worldwide reef crisis. Cryopreservation is an important intervention measure and a vital component of the modern coral conservation toolkit, but preservation techniques are currently limited to sensitive reproductive materials that can only be obtained a few nights per year during spawning. Here, we report the successful cryopreservation and revival of cm-scale coral fragments via mL-scale isochoric vitrification. We demonstrate coral viability at 24 h post-thaw using a calibrated oxygen-uptake respirometry technique, and further show that the method can be applied in a passive, electronics-free configuration. Finally, we detail a complete prototype coral cryopreservation pipeline, which provides a platform for essential next steps in modulating post-thaw stress and initiating long-term growth. These findings pave the way towards an approach that can be rapidly deployed around the world to secure the biological genetic diversity of our vanishing coral reefs.

Solar radiation, temperature and the reproductive biology of the coral Lobactis scutaria in a changing climate

Coral reefs worldwide are at risk due to climate change. Coral bleaching is becoming increasingly common and corals that survive bleaching events can suffer from temporary reproductive failure for several years. While water temperature is a key driver in causing coral bleaching, other environmental factors are involved, such as solar radiation. We investigated the individual and combined effects of temperature, photosynthetically active radiation (PAR), and ultraviolet radiation (UVR) on the spawning patterns and reproductive physiology of the Hawaiian mushroom coral Lobactis scutaria, using long-term experiments in aquaria. We examined effects on spawning timing, fertilisation success, and gamete physiology. Both warmer temperatures and filtering UVR altered the timing of spawning. Warmer temperatures caused a drop in fertilisation success. Warmer temperatures and higher PAR both negatively affected sperm and egg physiology. These results are concerning for the mushroom coral L. scutaria and similar reproductive data are urgently needed to predict future reproductive trends in other species. Nonetheless, thermal stress from global climate change will need to be adequately addressed to ensure the survival of reef-building corals in their natural environment throughout the next century and beyond. Until then, reproduction is likely to be increasingly impaired in a growing number of coral species.

Lipid profiling in chilled coral larvae

Coral reefs are disappearing worldwide as a result of several harmful human activities. The establishment of cryobanks can secure a future for these ecosystems. To design effective cryopreservation protocols, basic proprieties such as chilling tolerance and lipid content must be assessed. In the present study, we investigated chilling sensitivity and the effect of chilling exposure on the lipid content and composition of larvae belonging to 2 common Indo-Pacific corals: Seriatopora caliendrum and Pocillopora verrucosa. The viability of coral larvae incubated with 0.5, 1, and 2 M ethylene glycol (EG), propylene glycol (PG), dimethyl sulfoxide (Me₂SO), methanol, or glycerol and kept at 5 °C for different time periods was documented. In addition, we investigated the content of cholesterol, triacylglycerol (TAG), wax ester (WE), sterol ester (SE), lysophosphatidylcholine, phosphatidylcholine, phosphatidylethanolamine, and several fatty acid (FA) classes in coral propagules incubated with 1 M PG or EG and kept at 5 °C for 6 h. Moreover, we examined seasonal changes in the aforementioned lipid classes in coral larvae. S. caliendrum incubated with 0.5 M PG or Me₂SO and chilled for 2 h exhibited a viability rate of 11 ± 11%, whereas P. verrucosa exhibited a viability rate of 22 ± 14% after being chilled for 4 h. Furthermore, the results indicated that chilling exposure did not affect the content of any investigated lipid class in either species. The higher concentration of SE in P. verrucosa compared to S. caliendrum larvae may have contributed to the different cryotolerance displayed by the 2 larval species. A year-round lipid analysis of both coral larvae species revealed trends of homeoviscous adaptation and seasonal enhancement of lipid fluxes from symbionts to the host. During winter, the cholesterol/phospholipid ratio significantly increased, and P. verrucosa larvae exhibited an averagely decrease in FA chain lengths. During spring and summer, intracellular lipid content in the form of TAGs and WEs significantly increased in both species, and the average content of Symbiodiniaceae-derived FAs increased in P. verrucosa larvae. We concluded that the low cryotolerance displayed by S. caliendrum and P. verrucosa larvae is attributable to their chilling-sensitive membrane lipid profile and the high intracellular lipid content provided by their endosymbionts.

Supplementation of exogenous lipids via liposomes improves coral larvae settlement post-cryopreservation and nano-laser warming

Coral reefs worldwide are receding because of detrimental human activities, and cryopreservation of coral larvae would ensure that their genetic biodiversity is not irremediably lost. In recent years, the vitrification and laser warming of coral propagules has demonstrated promising results. During cryopreservation, cellular membranes undergo substantial reconfigurations that may affect survival. Fat enrichment may alter the physical proprieties of cell membranes and improve resistance to low temperatures. Therefore, the aim of this study was to determine whether supplementation of exogenous lipids using liposomes would improve cryosurvival and further development of the vitrified and laser-warmed coral larvae of Seriatopora caliendrum and Pocillopora verrucosa. A vitrification solution (VS) composed of 2 M ethylene glycol (EG), 1 M propylene glycol (PG), 40% (w/v) Ficoll, and 10% gold nanoparticles (at a final concentration of 1.2 × 10¹⁸ particles/m³ and an optimised emission wavelength of 535 nm) was chosen. Coral larvae were subjected to vitrification with VS incorporating one of four lipid classes: phosphatidylcholine (PC), phosphatidylethanolamine (PE), erucic acid (EA), and linoleic acid (LA). Warming was achieved using a single laser pulse (300 V, 10 ms pulse width, 2 mm laser beam diameter). A significantly higher vitality rate was observed in S. caliendrum larvae subjected to vitrification and laser warming with EA-incorporated VS, and P. verrucosa larvae vitrified and laser warmed using PE-incorporated VS achieved a significantly higher settlement rate. Our study demonstrated that supplementation of exogenous lipids with liposomes enhances coral larvae cryotolerance and improves cryopreservation outcomes. Lipid enrichment may play a key role in cryobanking coral propagules, and in propagule development after thawing.

The World Coral Conservatory (WCC): A Noah's ark for corals to support survival of reef ecosystems

Global change causes widespread decline of coral reefs. In order to counter the anticipated disappearance of coral reefs by the end of this century, many initiatives are emerging, including creation of marine protected areas (MPAs), reef restoration projects, and assisted evolution initiatives. Such efforts, although critically important, are locally constrained. We propose to build a “Noah's Ark” biological repository for corals that taps into the network of the world’s public aquaria and coral reef scientists. Public aquaria will serve not only as a reservoir for the purpose of conservation, restoration, and research of reef-building corals but also as a laboratory for the implementation of operations for the selection of stress-resilient and resistant genotypes. The proposed project will provide a global dimension to coral reef education and protection as a result of the involvement of a network of public and private aquaria.

Global change is causing a widespread decline in coral reefs. This Community Page article proposes to build the World Coral Conservatory, a “Noah's Ark” biological repository that taps into the network of the world’s public aquaria and coral reef scientists, in order to preserve the fast-disappearing biodiversity of coral reefs.

Successful cryopreservation of coral larvae using vitrification and laser warming

Climate change has increased the incidence of coral bleaching events, resulting in the loss of ecosystem function and biodiversity on reefs around the world. As reef degradation accelerates, the need for innovative restoration tools has become acute. Despite past successes with ultra-low temperature storage of coral sperm to conserve genetic diversity, cryopreservation of larvae has remained elusive due to their large volume, membrane complexity, and sensitivity to chilling injury. Here we show for the first time that coral larvae can survive cryopreservation and resume swimming after warming. Vitrification in a 3.5 M cryoprotectant solution (10% v/v propylene glycol, 5% v/v dimethyl sulfoxide, and 1 M trehalose in phosphate buffered saline) followed by warming at a rate of approximately 4,500,000 °C/min with an infrared laser resulted in up to 43% survival of Fungia scutaria larvae on day 2 post-fertilization. Surviving larvae swam and continued to develop for at least 12 hours after laser-warming. This technology will enable biobanking of coral larvae to secure biodiversity, and, if managed in a high-throughput manner where millions of larvae in a species are frozen at one time, could become an invaluable research and conservation tool to help restore and diversify wild reef habitats.

Cryobiology: principles, species conservation and benefits for coral reefs

Coral reefs are some of the oldest, most diverse and valuable ecosystems on Earth because they can support one-quarter of all marine life in our oceans. Despite their importance, the world’s coral reefs continue to be degraded at unprecedented rates by local and global threats that are warming and creating a more acidic ocean. This paper explores the reproductive challenges of coral for ex situ conservation, using IVF and cryopreservation, and our practical biobanking methods. Coral present challenges for cryopreservation because their reproductive period is often limited to a few nights yearly, they are mostly hermaphrodites with diverse modes of reproduction, including asexual reproduction (i.e. fragmentation and parthenogenesis) and sexual reproduction (i.e. self- and cross-fertilisation) and they express physiological toxins that can inhibit cryopreservation. We have banked spermatozoa from 12 coral species using the same field-hardy methods and have created new coral with thawed spermatozoa. In addition, we describe the cryopreservation of coral symbionts, whose physiology only permits the highest success seasonally. As part of a multidisciplinary conservation strategy, these collections may provide a major hedge against extinction for corals facing the damaging effects of climate change and loss of genetic diversity, and promise to help offset threats to our reefs worldwide.

Potential bleaching effects on coral reproduction

Bleaching profoundly impacts coral reproduction, often for years after an event. However, detailed reproductive characteristics of coral after bleaching have not been broadly described, especially as they relate to cryopreservation. Therefore, in the present study we measured several reproductive characteristics in coral in Kaneohe Bay, Hawaii, for two species, namely Fungia scutaria and Montipora capitata, during the bleaching period of 2014 and 2015. We examined spawning periods, egg morphometry, sperm concentration, fresh and cryopreserved sperm motility exposed to different concentrations of dimethyl sulfoxide, time of first cleavage, larval survival with fresh and cryopreserved spermatozoa, infection success and settlement success. Many of these reproductive parameters were reduced in 2015, especially sperm motility. Once the reduced-motility spermatozoa from 2015 post-bleach were cryopreserved, there was a steep decline in post-thaw viability and this would prevent any substantive further use of these samples in reproduction for conservation benefit. Worldwide, as bleaching events become more frequent, the ability to bank and conserve coral ex situ may be significantly reduced. Thus, it is imperative that while genetic diversity is still high in these populations, intensive efforts are made to bank coral species during non-bleaching periods.

Towards a vitrification-based cryopreservation protocol for the coral Pocillopora damicornis L.: Tolerance of tissue balls to 4.5 M cryoprotectant solutions

In this study, we tested the tolerance of tissue balls (TBs, 100-400 μm in diameter) from the coral Pocillopora damicornis produced using mechanical excision to exposure to cryoprotectant (CPA) solutions. TBs were treated for 20 min at room temperature with individual, binary, ternary or quaternary CPA solutions with a total molarity from 2.0 to 5.0M. Four CPAs were used: ethylene glycol (EG), dimethylsulfoxide (Me2SO), methanol (Met) and glycerol (Gly). In some experiments, the molarity of the CPA solutions was increased and decreased in a stepwise manner. The tolerance of TBs following CPA treatment was evaluated using two parameters. The Tissue Ball Regression (expressed in μm/h) measured the diameter regression of TBs over time. The % Undamaged TBs quantified the proportion of TBs, which remained intact over time after the CPA treatment. TBs tolerated exposure to binary solutions with a total molarity of 4.0 M containing 2.0 M EG+2.0 M Met and 2.0 MEG+2.0 M Gly. TBs displayed tolerance to ternary solutions with a total molarity up to 3.0 M, containing each CPA at 1.0 M. Quaternary solutions with a total molarity of 4.0M containing each CPA at 1.0 M were not tolerated by TBs. When the molarity of the CPA solutions was increased and decreased in a stepwise manner, TBs withstood exposure to a CPA solution with a total molarity of 4.5 M, containing 1.5 M EG+1.5 M Gly+1.5 M Me(2)SO. This study confirmed the interest of using TBs to test CPA solutions, with the objective of developing a vitrification-based cryopreservation protocol.

Trehalose is a chemical attractant in the establishment of coral symbiosis

Coral reefs have evolved with a crucial symbiosis between photosynthetic dinoflagellates (genus Symbiodinium) and their cnidarian hosts (Scleractinians). Most coral larvae take up Symbiodinium from their environment; however, the earliest steps in this process have been elusive. Here we demonstrate that the disaccharide trehalose may be an important signal from the symbiont to potential larval hosts. Symbiodinium freshly isolated from Fungia scutaria corals constantly released trehalose (but not sucrose, maltose or glucose) into seawater, and released glycerol only in the presence of coral tissue. Spawning Fungia adults increased symbiont number in their immediate area by excreting pellets of Symbiodinium, and when these naturally discharged Symbiodinium were cultured, they also released trehalose. In Y-maze experiments, coral larvae demonstrated chemoattractant and feeding behaviors only towards a chamber with trehalose or glycerol. Concomitantly, coral larvae and adult tissue, but not symbionts, had significant trehalase enzymatic activities, suggesting the capacity to utilize trehalose. Trehalase activity was developmentally regulated in F. scutaria larvae, rising as the time for symbiont uptake occurs. Consistent with the enzymatic assays, gene finding demonstrated the presence of a trehalase enzyme in the genome of a related coral, Acropora digitifera, and a likely trehalase in the transcriptome of F. scutaria. Taken together, these data suggest that adult F. scutaria seed the reef with Symbiodinium during spawning and the exuded Symbiodinium release trehalose into the environment, which acts as a chemoattractant for F. scutaria larvae and as an initiator of feeding behavior- the first stages toward establishing the coral-Symbiodinium relationship. Because trehalose is a fixed carbon compound, this cue would accurately demonstrate to the cnidarian larvae the photosynthetic ability of the potential symbiont in the ambient environment. To our knowledge, this is the first report of a chemical cue attracting the motile coral larvae to the symbiont.

Survival of tissue balls from the coral Pocillopora damicornis L. exposed to cryoprotectant solutions

In this study, the tolerance of tissue balls (TBs, 100-300 μm in diameter) from the coral Pocillopora damicornis produced using mechanical excision to exposure to cryoprotectant (CPA) solutions was tested. TBs were treated for 20 min at room temperature with solutions of ethylene glycol (EG), methanol (Met), glycerol (Gly) or dimethyl sulfoxide (Me2SO) at concentrations between 1.0 and 4.5M. Two parameters were used to evaluate the survival of TBs following CPA treatment. The Undamaged Duration of Tissue Balls (expressed in h) corresponded to the time period during which the membrane surface of TBs remained smooth and their motility was preserved. Tissue Ball Regression (expressed in μm/h) corresponded to the size reduction of TBs over time. TBs tolerated exposure to all CPAs tested at the three lower concentrations employed (1.0 M, 1.5 M and 2.0 M). No survival was achieved following exposure to a 4.5 M CPA solution. At concentrations of 3.0 and 4.0 M, higher Undamaged Duration of Tissue Balls and lower Tissue Ball Regression were obtained following treatment with EG compared to the other three CPAs. Our experiments show that TBs constitute a good experimental material to evaluate CPA toxicity on corals using large numbers of samples. Performing preliminary experiments with TBs may allow reducing the number of tests carried out with less easily available coral forms such as planulae, thereby preserving larval stocks.

The reality, use and potential for cryopreservation of coral reefs

Throughout the world coral reefs are being degraded at unprecedented rates. Locally, reefs are damaged by pollution, nutrient overload and sedimentation from out-dated land-use, fishing and mining practices. Globally, increased greenhouse gases are warming and acidifying oceans, making corals more susceptible to stress, bleaching and newly emerging diseases. The coupling of climate change impacts and local anthropogenic stressors has caused a widespread and well-recognized reef crisis. Although in situ conservation practices, such as the establishment and enforcement of marine protected areas, reduce these stressors and may help slow the loss of genetic diversity on reefs, the global effects of climate change will continue to cause population declines. Gamete cryopreservation has already acted as an effective insurance policy to maintain the genetic diversity of many wildlife species, but has only just begun to be explored for coral. Already we have had a great deal of success with cryopreserving sperm and larval cells from a variety of coral species. Building on this success, we have now begun to establish genetic banks using frozen samples, to help offset these threats to the Great Barrier Reef and other areas.

Lipid content and composition during the oocyte development of two gorgonian coral species in relation to low temperature preservation

Our previous studies have suggested that chilling sensitivity of coral oocytes may relate to their relatively high lipid intracellular content and lipid composition. The distribution of lipids during the oocyte development was determined here for the first time in two gorgonian species (Junceella juncea and Junceella fragilis). The main lipid classes in the two gorgonian oocytes were total lipid, wax ester, triacylglycerol, total fatty acid, phosphatidylethanolamine and phosphatidylcholine. The results indicated that early stage oocytes of J. juncea and J. fragilis were found to have increased lipid content than late stage oocytes. The content of wax ester was significantly higher in the early stage oocytes of two gorgonian corals (51.0±2.5 and 41.7±2.9 µg/mm(3)/oocyte) than those of late stage oocytes (24.0±1.4 and 30.4±1.2 µg/mm(3)/oocyte, respectively). A substantial amount of phosphatidylethanolamine and total fatty acid was detected at each stage of oocyte development in two gorgonian ranges from 107 to 42 µg/mm(3)/oocyte and 106 to 48 µg/mm(3)/oocyte, whilst low levels of phosphatidylcholine were found in two gorgonian oocytes. The levels of total lipid in the late stage oocytes of J. juncea were significantly higher than those of J. fragilis. The observed differences may partially be related to different habitat preferences as higher lipid levels in J. juncea, a deeper-water coral species exposed to lower temperature seawater, might relate to adjustments of cell membranes in order to increase membrane fluidity.

The effect of chilling and cryoprotectants on hard coral (Echinopora spp.) oocytes during short-term low temperature preservation

Understanding chilling sensitivity and chilling injury of coral oocytes, in the presence and absence of a cryoprotectant, is important in developing cryopreservation protocols, as well as for short-term storage and transport (e.g., for species conservation). The objective of this study was to investigate the chilling sensitivity of hard coral (Echinopora spp.) oocytes and the effectiveness of methanol (as a cryoprotectant) in protecting these oocytes during short-term, low temperature preservation. Oocytes were exposed to 0.5, 1, or 2 m methanol at 5, 0, or -5 °C for 1, 2, 4, 6, 8, 16, or 32 h, and their quality determined based on adenosine triphosphate (ATP) content. Methanol at 0.5 m was the most effective means to reduce chilling-induced reduction in ATP concentrations. Coral oocytes can be stored at room temperature for 4 h in filtered nature seawater with no detrimental effect on oocyte quality; however, in the present study, oocyte survival was extended for 8 h by addition of methanol in low concentrations (0.5 or 1 m) at low temperatures (5 and 0 °C). These findings should enhance conservation efforts and facilitate low-temperature transport of endangered and threatened coral species.

Analysis of internal osmolality in developing coral larvae, Fungia scutaria

Coral species throughout the world are facing severe local and global environmental pressures. Because of the pressing conservation need, we are studying the reproduction, physiology, and cryobiology of coral larvae with the future goal of cryopreserving and maintaining these organisms in a genome resource bank. Effective cryopreservation involves several steps, including the loading and unloading of cells with cryoprotectant and the avoidance of osmotic shock. In this study, during the time course of coral larvae development of the mushroom coral Fungia scutaria, we examined several physiologic factors, including internal osmolality, percent osmotically active water, formation of mucus cells, and intracellular organic osmolytes. The osmotically inactive components of the cell, V(b), declined 33% during development from the oocyte to day 5. In contrast, measurements of the internal osmolality of coral larvae indicated that the internal osmolality was increasing from day 1 to day 5, probably as a result of the development of mucus cells that bind ions. Because of this, we conclude that coral larvae are osmoconformers with an internal osmolality of about 1,000 mOsm. Glycine betaine, comprising more than 90% of the organic osmolytes, was found to be the major organic osmolyte in the larvae. Glycerol was found in only small quantities in larvae that had been infected with zooxanthellae, suggesting that this solute did not play a significant role in the osmotic balance of this larval coral. We were interested in changes in cellular characteristics and osmolytes that might suggest solutes to test as cryoprotectants in order to assist in the successful cryopreservation of the larvae. More importantly, these data begin to reveal the basic physiological events that underlie the move from autonomous living to symbiosis.

Use of an adenosine triphosphate assay, and simultaneous staining with fluorescein diacetate and propidium iodide, to evaluate the effects of cryoprotectants on hard coral (Echinopora spp.) oocytes

The objective was to examine the effects of cryoprotectants on oocytes of hard corals (Echinopora spp.) to obtain basic knowledge for cryopreservation procedures. Oocytes were exposed to various concentrations of cryoprotectants (0.25 to 5.0M) for 20 min at room temperature (25 degrees C). Two tests were used to assess ovarian follicle viability: fluorescein diacetate (FDA)+propidium iodide (PI) staining, and adenosine triphosphate (ATP) assay. Both FDA+PI staining and ATP assay indicated that cryoprotectant toxicity to oocytes increased in the order methanol, dimethyl sulfoxide (DMSO), propylene glycol (PG), and ethylene glycol (EG). The no observed effect concentrations for Echinopora spp. oocytes were 1.0, 0.5, 0.25, and 0.25 M for methanol, DMSO, PG, and EG, respectively, when assessed with FDA+PI. The ATP assay was more sensitive than FDA+PI staining (P<0.05). Oocyte viability after 1.0M methanol, DMSO, EG, or PG treatment for 20 min at room temperature assessed with FDA+PI tests and ATP assay were 88.9+/-3.1% and 72.2+/-4.4%, 66.2+/-5.0% and 23.2+/-4.9%, 58.9+/-5.4% and 1.1+/-0.7%, and 49.1+/-5.1% and 0.9+/-0.5%, respectively. We inferred that the ATP assay was a valuable measure of cellular injury after cryoprotectant incubation. The results of this study provided a basis for development of protocols to cryopreserve coral oocytes.

Physiology and cryosensitivity of coral endosymbiotic algae (Symbiodinium)

Coral throughout the world are under threat. To save coral via cryopreservation methods, the Symbiodinium algae that live within many coral cells must also be considered. Coral juvenile must often take up these important cells from their surrounding water and when adult coral bleach, they lose their endosymbiotic algae and will die if they are not regained. The focus of this paper was to understand some of the cryo-physiology of the endosymbiotic algae, Symbiodinium, living within three species of Hawaiian coral, Fungia scutaria, Porites compressa and Pocillopora damicornis in Kaneohe Bay, Hawaii. Although cryopreservation of algae is common, the successful cryopreservation of these important coral endosymbionts is not common, and these species are often maintained in live serial cultures within stock centers worldwide. Freshly-extracted Symbiodinium were exposed to cryobiologically appropriate physiological stresses and their viability assessed with a Pulse Amplitude Fluorometer. Stresses included sensitivity to chilling temperatures, osmotic stress, and toxic effects of various concentrations and types of cryoprotectants (i.e., dimethyl sulfoxide, propylene glycol, glycerol and methanol). To determine the water and cryoprotectant permeabilities of Symbiodinium, uptake of radio-labeled glycerol and heavy water (D(2)O) were measured. The three different Symbiodinium subtypes studied demonstrated remarkable similarities in their morphology, sensitivity to cryoprotectants and permeability characteristics; however, they differed greatly in their sensitivity to hypo- and hyposmotic challenges and sensitivity to chilling, suggesting that standard slow freezing cryopreservation may not work well for all Symbiodinium. An appendix describes our H(2)O:D(2)O water exchange experiments and compares the diffusionally determined permeability with the two parameter model osmotic permeability.

Preliminary studies of sperm cryopreservation in the mushroom coral, Fungia scutaria

Coral species throughout the world are facing severe environmental pressures. Because of this, we began cryobiological studies on the sperm of the mushroom coral, Fungia scutaria. We determined that F. scutaria sperm had a mean length of 56 microm and head diameter of 2.5 microm, and a mean spontaneous ice nucleation temperature of -37.2 +/- 1.7 degrees C. When the sperm were exposed to the cryoprotectant glycerol for 5 or 20 min (at 10% v/v), no fertilized larvae were produced. However, when sperm were exposed for 20 min to propylene glycol (10% v/v), fertilizations were produced at the same rate as untreated control eggs and sperm (P > 0.05), but slightly less for dimethyl sulfoxide (10% v/v) (P < 0.05). Regardless, dimethyl sulfoxide caused less osmotic damage to the sperm membrane than did propylene glycol. Therefore, we used the dimethyl sulfoxide (10% v/v) to develop cryopreservation protocols that yielded good post-thaw morphology and motility (>95%) for coral sperm.