Extending the natural adaptive capacity of coral holobionts

Abstract

Tropical coral reefs cover only 0.1% of the seafloor yet provide habitat for >30% of all marine multicellular species 1 . Ecosystem services delivered through healthy tropical reefs are economically valued at around US $9,900,000 million per year 2 and sustain almost a billion people [3][4][5] . Despite their importance, catastrophic global loss of coral reefs owing to anthropogenic activity is fast becoming a reality 6 . For example, the 2015-2018 global coral bleaching event affected 74% of reefs worldwide, with >30% of coral cover lost on the Great Barrier Reef alone 7 . Additionally, coral cover in the Florida Reef Tract has declined by upwards of 90% over the last 50 years [8][9][10][11] .A global contributing factor to reef degradation is coral bleaching 12,13 . Without their microalgal symbionts (Fig. 1), corals lose their primary source of nutrition, leading to starvation, reduced fecundity, and reduced growth, often resulting in widespread coral mortality 14,15 . Trajectories for coral reefs under present CO 2 emission scenarios are dire, with 60% of all remaining coral reefs critically threatened, and 98% exposed to environmental conditions above the current thresholds considered necessary to maintain ecosystem function as soon as 2030 (reF. 16 ). The impact of ocean warming is exacerbated by the effects of ocean acidification 17 , deoxygenation 18 , and salinity changes 19 . Combined with local factors such as overfishing, coastal development, disturbance of the nutrient environment (water quality), and disease or predator outbreaks, the interrelated cumulative impacts all contribute to reduction in coral cover and declining reef ecosystem health [20][21][22][23][24][25][26][27] .Given the rate and extent at which climate change unfolds 28 , a widespread and shared concern is that the rate of environmental change could outpace the ability of coral holobionts to adapt to the changing environment 29 , concomitant with the increasing loss of coral reef cover 30 . Global mitigation of CO 2 emissions is unquestionably needed to stem the rate of declining reef health [30][31][32] . However, biological, ecological and socio-economic adaptations are critical partners to preserve reefs and delay the loss of coral populations until carbon mitigation is effectively implemented 30 . Reef protection through Marine Protected Areas and management practices reduces how local stressors compound global climate change impacts 27,31 . Nevertheless, the current state of reefs and their predicted further decline have sparked initiatives to prioritize reefs or corals that are less vulnerable to climate change and best positioned for regenerating other degraded reefs in the future [33][34][35] . Coral bleachingDiscolouration of coral tissue due to the loss of microalgal symbionts triggered by climate change-induced ocean warming and thermal stress anomalies.

Antibiotics Alter Pocillopora Coral-Symbiodiniaceae-Bacteria Interactions and Cause Microbial Dysbiosis During Heat Stress

“…Future work would also benefit from the inclusion of baseline samples and additional time points to track the temporal changes in bacteria community composition and transcriptome responses across coral colonies. Collectively, the results of this experiment highlight the vital importance of coral-associated bacteria communities to coral holobiont metabolism, immunity, and acute heat stress responses, and provide a basis for future mechanistic studies of how symbiotic interactions between multiple partners shape coral holobiont health, evolution, and ecological resilience (Engelberts et al, 2021;Voolstra et al, 2021).…”

“…However, despite the critical importance of coral-associated bacteria to holobiont health, no study has simultaneously assessed coral holobiont transcriptome and microbiome responses to acute heat stress following direct antibiotic suppression of the native bacteria community. These studies are needed to better understand the role of coral-associated bacteria in coral holobiont health and heat tolerance, and to inform ongoing efforts that seek to conserve and restore coral reef ecosystems by enhancing corals' natural resilience through the application of beneficial microbes (Peixoto et al, 2021;Voolstra et al, 2021).…”

Highly Variable and Non-complex Diazotroph Communities in Corals From Ambient and High CO2 Environments

“…The resulting metaorganism is commonly referred to as the coral holobiont (Knowlton and Rohwer, 2003;Jaspers et al, 2019). Besides endosymbiotic dinoflagellate algae of the family Symbiodiniaceae that transfer photosynthetically fixed carbon to other holobiont constituents in exchange for shelter and inorganic nutrients (Muscatine and Porter, 1977;LaJeunesse et al, 2018), associated microbes include bacteria, archaea, fungi, and viruses that all contribute to coral holobiont physiology and stress resilience (Bourne et al, 2016;Peixoto et al, 2021;Voolstra et al, 2021). Although corals can cover almost up to 100% of their carbon demand via nutrient exchange with their endosymbiotic algae (Falkowski et al, 1984;Muscatine, 1990), biomass synthesis requires the supplementation of translocated carbon with other nutrients (e.g., nitrogen).…”

Ecosystem design as an avenue for improving services provided by carbonate producing marine ecosystems

“…Additionally, the project includes elements of future-proofing the coral reefs against increasing occurrences of marine heat waves ( Osman et al, 2018 ) by planning for multiple coral nurseries with the potential to interbreed coral species to develop thermal resilience ( Chalastani et al, 2020 ). While the approach of selective breeding and outplanting to improve thermal tolerance and long-term resilience is still in its infancy and requires substantial ecological risk–benefit assessments ( Voolstra et al, 2021 ; Kleypas et al, 2021 ) the Red Sea project offers the chance to acquire data on the success of such approaches.…”