A Research Review of Interventions to Increase the Persistence and Resilience of Coral Reefs (2019) / Chapter Skim
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6 Conclusion
6 Conclusion
Pages 163-176
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From page 163... ...
On the other hand, coral reef ecosystems are existentially threatened by increased human-driven stresses, particularly the extensive coral mortality from severe bleaching events caused by warming seas on top of local stressors such as sedimentation, pollution, invasive species, and overfishing. Continuing disease threats and concerns about increasingly acidifying waters compound the risk posed to coral reefs.
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From page 164... ...
However, even with such reductions, committed warming from the current accumulation of greenhouse gases is expected to expose the majority of the world's reefs to harmful thermal stress events annually by 2050. Global bleaching events are already occurring due to the sensitivity of coral reefs to even small, sustained increases in maximum temperatures (as low as 1°C)
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From page 165... ...
Novel Communities A key feature of any intervention scheme for coral reefs is the movement of coral colonies to areas where they are needed to support reef stability. Whether new adaptive capacity is found on native reefs or generated in the laboratory, the most tolerant corals are likely to be a subset of the population with the expectation that this tolerance is heritable and will spread.
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From page 166... ...
TABLE 6.1 Overview of Interventions Examined in This Report 166 Intervention What It Is Current Feasibility Potential Scale Limitations Risks Genetic and Reproductive Interventions Managed Creating increased In laboratory and at Local reef scale; Needs large Decrease in genetic Selection frequency of existing small local scales potentially populations variation tolerance genes transgenerational Managed Enhancing Success with some Local reef Depends on sufficient Decrease in genetic Breeding: population size by species at small scales population; population sampling variation Supportive captive rearing and potentially and recruitment Breeding release transgenerational success of released individuals Managed Introducing Demonstrated in Local reef Requires transport of Outbreeding Breeding: diversity from other laboratory for a few population; gametes or colonies depression; native Outcrossing populations through species potentially across distances and genotypes may be Between breeding transgenerational field testing across swamped Populations generations Managed Creation of novel Demonstrated in Local reef Limited ability to Outbreeding Breeding: genotypes through laboratory for a few population; create hybrids; requires depression; competition Hybridization breeding species potentially testing for fertility and with native species Between Species transgenerational fitness Gamete and Collection and Feasible at local scales Laboratory to Site-specific Limited genetic Larval Capture manipulation in the local reef scale; reproductive timing, diversity; selection for and Seeding field and laboratory potentially recruitment success can laboratory versus field and release into the transgenerational be poor success wild Coral Frozen storage of Feasibility is high for Materials can Requires excess Long-term survival Cryopreservation gametes and other sperm, and growing be transported gametes, larvae, or uncertain; genetic cells for later use and for other tissue types globally tissues variation reflects only transport current conditions
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From page 167... ...
Genetic Altering coral genes Technically feasible Would occur in Gene targets and Might alter wrong Manipulation: for new function for larvae laboratory; can be cellular raw material genes; unknown risks Coral self-perpetuating unidentified, long lead time to roll out to reefs Genetic Altering symbiont Not yet feasible Would occur in Technology not Might alter wrong Manipulation: genes for new laboratory; can be established; gene genes; kill target cells; Symbionts function self-perpetuating targets and cellular raw unknown risks material unidentified Physiological Interventions Pre-exposure Using stress exposure In laboratory and Local reef scale; Difficult to scale up Could be detrimental if to make colonies small-scale field trials may be temporary beyond local applied incorrectly more tolerant or transgenerational Algal Symbiont Changing algal Observed after Individual coral Difficult to scale; easier Ecological tradeoffs, Manipulation symbionts to more bleaching events; colony or large for some coral species e.g., slower growth tolerant types demonstrated in spawning events; than others laboratory unknown longevity Microbiome Maintaining/ Demonstrated in Locations on Reef-wide delivery Potential to increase Manipulation increasing abundance laboratory and reefs to reef scale; mechanisms are deleterious microbes, of the native or new nursery facilities for applied at times of lacking; lack of known decrease beneficial ones beneficial microbes limited coral species stress beneficial microbes; little understanding of direct or indirect effects Antibiotics Adding antibiotics to Used in aquaculture Laboratory, Lack of specificity to Promote antibiotic control pathogenic and demonstration in aquarium, and target pathogens limits resistance in microbes small-scale field trials colonies on reef; effectiveness deleterious microbes; requires repeated destabilization of application native beneficial microbiomes 167 continued
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From page 168... ...
TABLE 6.1 Continued 168 Intervention What It Is Current Feasibility Potential Scale Limitations Risks Phage Therapy Adding phage Demonstrated Local reef scale; Lack of identified Undesirable gene viruses to control in laboratory potential to self- target coral pathogens transfers across pathogenic microbes experiments propagate microbial populations; impact on beneficial microbes Antioxidants Reducing cellular Demonstrated in Laboratory only; Little understanding of May affect other reef oxidative damage some laboratory requires repeated direct or indirect effects species derived from stress experiments application using chemical treatments Nutritional Using nutrients Regular use in Laboratory Poor understanding of Shifts carbon, nitrogen, Supplementation to improve fitness coral research and and aquarium; balanced coral diets; and phosphate balance and increase stress aquaculture requires repeated reef-wide delivery and may benefit coral tolerance application mechanisms are lacking competitors Coral Population and Community Interventions Managed Increasing abundance Technically feasible Regional reef scale; Uncertain maintenance Moving nontarget Relocation: of stress-tolerant with information gaps can be permanent of stress tolerance over genes; ecological Assisted Gene genes or colonies regarding successful time tradeoffs Flow within population methods range Managed Moving stress- Technically feasible Regional reef scale; Uncertain maintenance Moving nontarget Relocation: tolerant or diverse with information gaps can be permanent of stress tolerance and genes, species, and Assisted Migration genes or colonies just regarding project persistence over time microbes; ecological outside species' range design between locations tradeoffs
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From page 169... ...
regimes Abiotic Ocean Reducing CO2 levels Effective in small- Sites within reefs Costly to scale up Impact of chemicals on Acidification chemically scale laboratory depending on chemical quantities environment Interventions experiments environmental setting; requires consistent input Seagrass Meadows Reducing daytime Some efficacy shown Local reefs Limited environmental Detritus; altered and Macroalgal CO2 levels in field measurements depending on settings; need to nutrient loads; Beds biologically environmental remove macroalgae competition from setting; long-term macroalgae; increased benefit CO2 at night 169
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From page 170... ...
The microbiome impacts coral health in multiple ways that are not yet completely understood, and shifting the microbiome may have unintended consequences on health. A clear concern known from other fields is that the overuse of antibiotics, especially in open systems, can result in the emergence of unwanted antibiotic-resistant bacteria.
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From page 171... ...
Microbial communities associated with corals are highly diverse complexes with a wide spectrum of functions that impact the health and potential heat tolerance of the coral holobiont. Understanding the role of this microbiome in the physiological response of corals to their surrounding environment is just beginning.
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From page 172... ...
Nevertheless, the ability to deploy this type of transient protection in the future may be important to protect high-value, live reef environments on local scales. CONSIDERATIONS FOR IMPLEMENTATION The task for this report is to synthesize current knowledge and lay the groundwork for informed decisions about conserving coral reefs under climate change.
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From page 173... ...
Due to the urgency of initiating responses to growing coral reef losses, identification of management and policy challenges is an important consideration along with scientific and technical challenges. Adaptive Management The interventions discussed in this report have not been implemented beyond experimental scales in the ocean, if at all, making their efficacy and impacts uncertain.
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From page 174... ...
can inform achievement of the goal of maintaining functional coral reef ecosystems. Monitoring potential drivers of failure (e.g., local stressors and conditions such as herbivore population sizes and sedimentation and pollution loads)
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From page 175... ...
and to the risk of doing nothing is an important consideration, and one that will be dependent on the state of the environment and predicted risks to coral persistence. The remainder of the committee's task, to be documented in a subsequent report, is to provide a framework for evaluating the relative risks and benefits of implementing these interventions.
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