Increases in seawater temperature associated with global climate change are causing the mutualistic relationship between reef-building corals and the symbiotic dinoflagellates (genus Symbiodinium) that reside within their cells to break down. There is consequently an urgent need to develop tools for modeling coral biology in response to environmental shifts, an enterprise that is complicated by the fact that no pristine reefs remain on Earth. This work sought to 1) uncover the environmental factors that contribute most to observed spatio-temporal variation in coral physiology and 2) devise means of detecting anomalous behavior in field corals by analyzing a dataset from the Austral (French Polynesia) and Cook Islands of the South Pacific with a multivariate statistical approach. Upon employing this multi-tiered analytical platform, host genotype was found to be the most significant driver of variation in physiology of the pocilloporid coral colonies sampled across the two archipelagos. Furthermore, those colonies demonstrating the most extensive variation across the seven response variables assessed tended to deviate most significantly from the global mean response calculated across all samples, suggesting that high within-sample physiological variability may be one means of delineating aberrant coral behavior in the absence of data from pristine control reefs.
Scientists have advocated for local interventions, such as creating marine protected areas and implementing fishery restrictions, as ways to mitigate local stressors to limit the effects of climate change on reef-building corals. However, in a literature review, we find little empirical support for the notion of managed resilience. We outline some reasons for why marine protected areas and the protection of herbivorous fish (especially parrotfish) have had little effect on coral resilience. One key explanation is that the impacts of local stressors (e.g., pollution and fishing) are often swamped by the much greater effect of ocean warming on corals. Another is the sheer complexity (including numerous context dependencies) of the five cascading links assumed by the managed-resilience hypothesis. If reefs cannot be saved by local actions alone, then it is time to face reef degradation head-on, by directly addressing anthropogenic climate change—the root cause of global coral decline.
The Red Sea is a unique body of water, hosting some of the most productive and diverse coral reefs. Human populations along coasts of the Red Sea were initially sparse due to the hot and arid climate surrounding it, but this is changing with improved desalination techniques, accessible energy, and increased economic interest in coastal areas. In addition to increasing pressure on reefs from coastal development, global drivers, primarily ocean acidification and seawater warming, are threatening coral reefs of the region. While reefs in southern sections of the Red Sea live near or above their maximum temperature tolerance and have experienced bleaching events in the recent past, coral reefs in northern sections are considered a coral reef refugia from global warming and acidification, at least for the coming decades. Such differential sensitivities along the latitudinal gradient of the Red Sea require differential solutions and management. In an effort to identify the appropriate solutions to conserve and maintain resilience of these reefs along a latitudinal gradient, we used a SWOT analysis (strengths/weaknesses/opportunities/threats) to frame the present situation and to propose policy solutions as useful planning procedures. We highlight the need for immediate action to secure the northern sections of the Red Sea as a coral reef climate change refuge by management and removal of local stressors. There is a need to strengthen the scientific knowledge base for proper management and to encourage regional collaboration on environmental issues. Based on scientific data, solutions such as marine protected areas, fishing regulation, and reef restoration approaches were ranked for five distinct latitudinal sections in the Red Sea and levels of interventions are recommended.
Global environmental change has the potential to disrupt well established species interactions, with impacts on nutrient cycling and ecosystem function. On coral reefs, fish living within the branches of coral colonies can promote coral performance, and it has been hypothesized that the enhanced water flow and nutrients provided by fish to corals could ameliorate coral bleaching. The aim of this study was to evaluate the influence of small, aggregating damselfish on the health of their host corals (physiology, recovery, and survival) before, during, and after a thermal-bleaching event. When comparing coral colonies with and without fish, those with resident fish exhibited higher Symbiodinium densities and chlorophyll in both field and experimentally-induced bleaching conditions, and higher protein concentrations in field colonies. Additionally, colonies with damselfish in aquaria exhibited both higher photosynthetic efficiency (FV/FM) during bleaching stress and post-bleaching recovery, compared to uninhabited colonies. These results demonstrate that symbiotic damselfishes, and the services they provide, translate into measureable impacts on coral tissue, and can influence coral bleaching susceptibility/resilience and recovery. By mediating how external abiotic stressors influence coral colony health, damselfish can affect the functional responses of these interspecific interactions in a warming ocean.
Sexually produced larvae are used in various fields of coral research. Because the vast majority of scleractinians reproduces only on one or few occasions per year through simultaneous release of gametes, and because an ex situspawning induction is still very hard to achieve, great efforts are required to obtain planula larvae. Brooding corals have been used to harvest planulae although their larvae often differ in various traits from most spawning corals, e.g., in settlement behavior. Other cnidarians, such as Aiptasia spp., have been substituting for scleractinians in many aspects of coral research. However, organisms such as Aiptasia differ strongly from scleractinians, thus limiting the transferability of obtained results. This study examines the potential of Leptastrea purpurea as a reliable source of larvae for coral research. Larval output as well as settlement behavior of planulae was investigated. Our results show that colonies of L. purpurea released a daily average of 3.7 (±0.2) larvae during a period of 65 days, thus allowing continual access to planula larvae. We collected a total of 58127 larvae from our broodstock of 243 colonies. Larval settlement is induced by the same and/or similar cues as in many spawning species which increases the transferability of conclusions. We discuss the utility of L. purpurea for research on scleractinian physiology, ecology and larval settlement and conclude that L. purpurea is a well-suited organism to accelerate progress in many fields of coral research.
Coral reef ecosystems provide many important services to society. Their importance is not only proved by their beauty but also because they provide food and livelihood for millions of people in communities around the world, especially in developing countries. This paper estimates the economic value of coral ecosystems and potential impacts of climate change and fishing activities on the loss of coral reefs in Nha Trang Bay, Vietnam. Economic valuation and bioeconomic approaches are applied to combine socioeconomic data and projections of coral reef cover based on the quantitative scenarios of sea surface temperature and fishing activity to articulate the potential economic consequences of future change in the coral reef. The loss in economic value of coral under climate change and fishing effort scenarios is estimated which ranges from US$27.78 to US$31.72 million annually. This result is useful for policy makers to draw conclusions for climate policy, biodiversity conservation, sustainable development, and priorities for further work.
Ocean warming (OW) and ocean acidification (OA) are threatening coral reef ecosystems, with a bleak future forecast for reef‐building corals, which are already experiencing global declines in abundance. In contrast, many coral reef sponge species are able to tolerate climate change conditions projected for 2100. To increase our understanding of the mechanisms underpinning this tolerance, we explored the lipid and fatty acid (FA) composition of four sponge species with differing sensitivities to climate change, experimentally exposed to OW and OA levels predicted for 2100, under two CO2Representative Concentration Pathways. Sponges with greater concentrations of storage lipid, phospholipids, sterols and elevated concentrations of n‐3 and n‐6 long‐chain polyunsaturated FA (LC PUFA), were more resistant to OW. Such biochemical constituents likely contribute to the ability of these sponges to maintain membrane function and cell homeostasis in the face of environmental change. Our results suggest that n‐3 and n‐6 LC PUFA are important components of the sponge stress response potentially via chain elongation and the eicosanoid stress‐signalling pathways. The capacity for sponges to compositionally alter their membrane lipids in response to stress was also explored using a number of specific homeoviscous adaptation (HVA) indicators. This revealed a potential mechanism via which additional CO2 could facilitate the resistance of phototrophic sponges to thermal stress through an increased synthesis of membrane‐stabilizing sterols. Finally, OW induced an increase in FA unsaturation in phototrophic sponges but a decrease in heterotrophic species, providing support for a difference in the thermal response pathway between the sponge host and the associated photosymbionts. Here we have shown that sponge lipids and FA are likely to be an important component of the sponge stress response and may play a role in facilitating sponge survival under future climate conditions.
Scleractinian corals’ microbial symbionts influence host health, yet how coral microbiomes assembled over evolution is not well understood. We survey bacterial and archaeal communities in phylogenetically diverse Australian corals representing more than 425 million years of diversification. We show that coral microbiomes are anatomically compartmentalized in both modern microbial ecology and evolutionary assembly. Coral mucus, tissue, and skeleton microbiomes differ in microbial community composition, richness, and response to host vs. environmental drivers. We also find evidence of coral-microbe phylosymbiosis, in which coral microbiome composition and richness reflect coral phylogeny. Surprisingly, the coral skeleton represents the most biodiverse coral microbiome, and also shows the strongest evidence of phylosymbiosis. Interactions between bacterial and coral phylogeny significantly influence the abundance of four groups of bacteria–including Endozoicomonas-like bacteria, which divide into host-generalist and host-specific subclades. Together these results trace microbial symbiosis across anatomy during the evolution of a basal animal lineage.
The annual sea surface temperature increased at a rate of 0.038 to 0.074 °C/year in recent decade, and pH decreased at a rate of 0.012–0.014/year in two coastal waters of the South China Sea. Therefore, a culture experiment was conducted to study the effects of acidification and warming on coral calcification rates. The calcification of three coral species were significantly reduced during the exposure to elevated CO2, while other three coral species were not significantly affected. The reef coral Pocillopora damicornis was resistant to high CO2, but was not able to survive during the exposure to 33 °C in our culture experiments. Our findings suggested that some corals might not survive in tropical areas if coral could not adapt to warming rapidly, and subtropical coastal waters with temperature of <30 °C will serve as refugia for the corals resistant to high CO2 at the end of this century.
Coral reefs are important to the dive experience, suggesting the expected increase in coral bleaching events has the potential to alter global flows of dive tourists. There are a growing number of studies that suggest taking people's estimation of their options and ability to react to a threat into account provides a clearer picture of the decision to respond to a threat. This study applied Protection Motivation Theory (PMT) to help understand the motivational factors associated with intended adaptation to coral bleaching. Multiple regression analysis was used to analyze the effects of threat and coping appraisal variables. This study provided the first empirical evidence of scuba divers' response to marginal reef conditions, indicating that the majority of respondents would significantly alter their behavior in some way. PMT was able to explain between 12.8% and 47.7% of the variance in adaptation intentions, with response efficacy and self-efficacy consistently emerging as the strongest significant predictors. Consideration of multiple adaptation responses demonstrates the variability of model performance and highlights the need to consider the context of adaptation when interpreting results. Implications for future research and the dive tourism industry are discussed.