A Research Review of Interventions to Increase the Persistence and Resilience of Coral Reefs (2019) / Chapter Skim
Currently Skimming:
3 Physiological Interventions
3 Physiological Interventions
Pages 77-118
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 77... ...
For example, oxidative stress caused by high temperatures might be avoided by hosting more thermotolerant algal symbionts or having higher constitutive expression of heat shock proteins. Alternatively, high levels of oxidative stress might instead be managed using beneficial bacteria to detoxify reactive oxygen species as they are produced.
|
From page 78... ...
. Here, we use the term "pre-exposure" as a general term to refer to the deliberate exposure of an organism (in this case, reef corals and their symbionts)
|
From page 79... ...
changes in holobiont composition. These phenomena are described in Box 3.1 and in the Algal Symbiont Manipulation section.
|
From page 80... ...
and collected RNA-Seq data at 10 and 18 hours post heat-stress, as well as at 0 hours control. Algal symbionts were rapidly expelled in response to heat stress.
|
From page 81... ...
It appears that GBM plays a role in coral adaptation and transgenerational inheritance but it is a small effect and of unclear importance given the absence of a sequestered germline in a coral colony. GBM is a stable feature of coral gene regulation that marks highly expressed genes across generations.
|
From page 82... ...
For example, physiological changes in algal symbionts exposed to high light include changes in the abundance of symbionts, the amount of chlorophyll per cell, the size of photosynthetic units, and xanthophyll cycling capacity (Brown et al., 2002) , all of which can influence the subsequent bleaching tolerance of the coral host, while also differing in how long these responses last.
|
From page 83... ...
The timing of the exposure may be key. Examples include exposing adult corals to high temperatures during gametogenesis or larval development, rearing larvae or settling recruits under stressful conditions prior to their release to the reef, or bleaching corals during early spring and allowing them to recover on the reef during the warming summer months.
|
From page 84... ...
Similarly, pre-exposing larvae or recruits may be scalable, but only if an active larval rearing and seeding program is already in place. Chronic pre-exposure of adult corals in the nursery phase as part of an outplanting program may be more readily scalable, because it only involves identifying an appropriate location for the nursery.
|
From page 85... ...
Infrastructure Infrastructure needs depend on the life stage at which these preexposures might be implemented. Acute pre-exposure at the larval or recruit stage requires an active gamete/larvae collection and rearing program and an effective recruit seeding program.
|
From page 86... ...
Another approach that has been used to modify algal symbiont communities is to use artificial selection in the laboratory to experimentally produce symbiont lineages that are more thermotolerant (Chakravarti and van Oppen, 2018; Chakravarti et al., 2017)
|
From page 87... ...
. How to Do It Adult corals Although changes in algal symbiont communities have been observed in the field, typically in response to coral bleaching (Baker et al., 2004; LaJeunesse et al., 2009)
|
From page 88... ...
. Moreover, the degree of symbiont community change could be reliably predicted based on bleaching severity and the photochemical advantage of one symbiont over another in the coral species in question.
|
From page 89... ...
. The natural predisposition of most, if not all, coral larvae or juveniles to acquire algal symbionts from environmental sources (LaJeunesse et al., 2004, 2010a)
|
From page 90... ...
Symbiont manipulations might be included as part of restoration efforts involving the asexual propagation of adult corals in nurseries, because significant time is already being invested in fragmenting, propagating, and outplanting individual fragments. Treatments designed to modify algal symbiont communities might be incorporated into the design or placement
|
From page 91... ...
However, given the interest in developing methods for improving recruitment in these areas, this approach seems poised for potential inclusion into these methods as and when they are implemented. Potential Scale Adult corals Symbiont manipulations operate at the scale of the individual coral colony, and are thus subject to significant scaling limitations.
|
From page 92... ...
Therefore, the risk of symbiont manipulations failing is highly dependent on the identities of both the host and symbiont. Risks The manipulation of algal symbiont communities in favor of particular traits (such as higher thermotolerance)
|
From page 93... ...
As before, the changing environmental conditions are likely to determine to relative costs and benefits of having different symbionts. Tradeoffs in experimentally evolved Symbiodiniaceae are also likely to exist, although they have not been conclusively demonstrated to date (Chakravarti and van Oppen, 2018; Chakravarti et al., 2017)
|
From page 94... ...
New symbionts may be lost over time (LaJeunesse et al., 2010b; Thornhill et al., 2006a, 2006b) or experimentally evolved symbionts (Chakravarti and van Oppen, 2018; Chakravarti et al., 2017)
|
From page 95... ...
Costs are likely to be even lower to incorporate symbiont manipulations into a sexual restoration program involving larval rearing and assisted recruitment. In fact, the potential benefits and ease of introducing algal symbionts during coral early life stages are such that failing to incorporate such measures would probably represent a lost opportunity.
|
From page 96... ...
. Microbes occupy a variety of niches within the coral holobiont, and the ability to manipulate them for coral resilience depends on knowledge of their function and composition across these niches.
|
From page 97... ...
. The bacterial communities in the gastric cavity have been demonstrated to be high in vitamin B12 and hence provide important trace nutrients to the coral holobiont (Agostini et al., 2009)
|
From page 98... ...
, the resilience of corals to changing environments may be increased for existing coral populations, including a wide range of native species and genotypes, and potentially passed on to future generations. How to Do It There are a number of approaches that can be taken to manipulate the coral microbiome with the aim of improving the resilience of the coral host to environmental stress.
|
From page 99... ...
When added to corals that had also been challenged with the coral pathogen Vibrio coralliilyticus, the predatory bacterium ameliorated changes in the coral microbiome and prevented secondary colonization of opportunistic bacterial groups identified as indicators in compro mised coral health (see also Welsh et al., 2016, 2017)
|
From page 100... ...
These unknowns make it unlikely that benefits will be seen at the reef scales in the near term, but development of improved coral diets that include probiotics, and ways to manipulate the coral microbiome that promote environmental resilience, is potentially achievable with extensive research and development. Potential Scale The coral-associated microbiome is generally specific for coral species and even across populations of one species.
|
From page 101... ...
. Shifting the microbiome partners may also result in tradeoffs similar to those possible when shifting algal symbionts (i.e., confering thermal resilience but with reduced growth)
|
From page 102... ...
. Therefore, understanding the interactions of the members of the coral holobiont at the cellular level is critical to ensure any microbiome manipulation is directly facilitating improved coral fitness and resilience.
|
From page 103... ...
If suitable microbial cocktails are identified and developed, the next steps would be to integrate them into coral nurseries and outplanting sites, taking advantage of the infrastructure established for propagating corals. At these small scales, the costs would not be extensive and application would take advantage of technological applications in other fields, such as agriculture and food production, that currently implement probiotics or microbiome manipulation to boost production.
|
From page 104... ...
might thereafter increase their resilience to environmental stress. In the best-case scenarios therapeutic approaches may even cure that individual or population from impairment in function, for example in a disease outbreak.
|
From page 105... ...
Potential Scale Application of antibiotics in situ on coral reefs can be highly contentious, although it is feasible when applied at the scale of treating individual coral colonies. This approach is labor intensive and most efficiently applied in areas that have detailed information on the prevalence of the disease outbreak within the coral population, indicating where individual coral colonies can be targeted to potentially reduce the risk of disease spread.
|
From page 106... ...
. Application of antibiotics, especially as a preventative measure against disease, may therefore destabilize the healthy coral microbiome, making these coral colonies more susceptible to disease.
|
From page 107... ...
. Phage therapy has been a successful approach used in human medicines and was highly advanced especially in Eastern European countries prior to the widespread use of antibiotics (Abedon et al., 2017; Nobrega et al., 2015)
|
From page 108... ...
In addition, bacteriophages are highly specific to the target bacterial strains making it unlikely that other symbiotic microbes of the coral holobiont are affected (unlike broadspectrum antibiotics)
|
From page 109... ...
Bacteriophage have the potential to spread virulence traits across target and nontarget hosts. Some studies have highlighted that virulence and antibiotic resistance genes exist in some bacteriophage genomes, with the capacity to be passed into hosts that do not have these (Doss et al., 2017; Nobrega et al., 2015)
|
From page 110... ...
of ROS produced during extreme environmental conditions. Similarly, trace metals such as iron play a role in supporting algal symbiont photosynthesis and,
|
From page 111... ...
However, during environmental stress events such as high seawater temperature periods, particularly in doldrums conditions that promote high light penetration onto reefs, the capacity of the coral holobiont to maintain homeostasis in production and scavenging of ROS becomes disrupted in favor of production (Weis et al., 2008)
|
From page 112... ...
The efficacy of the approaches at reef scale would be highly dependent on finding an appropriate and efficient delivery method to benefit coral during times of stress and increased internal ROS production. At temporal scales, provided the approach is shown to be effective, addition of the antioxidants and other chemicals would be required during early and peak periods of environmental stress, and potentially even following the stress events to help coral recovery.
|
From page 113... ...
NUTRITIONAL SUPPLEMENTATION What It Is Nutritional supplementation of corals with carbon and other essential nutritional elements during periodic episodes of major stress events (e.g., bleaching that impacts their metabolic competence) represents an additional novel intervention strategy.
|
From page 114... ...
Within aquarium systems, supplementation of corals' energy requirements through heterotrophic feeding is already an established and essential requirement to maintain health. Benefit and Goals Interventions that deliver greater nutritional supplementation to coral may improve their resilience during times of environmental stress by compensating for the lost energy resulting from algal symbiont dysfunction during bleaching events.
|
From page 115... ...
On a temporal scale, nutritional supplements would be applied during early and peak periods of environmental stress, and potentially even following the stress events to help coral recovery. Risks Ecosystem-level impacts include the effect of the addition of excess labile carbon, nitrogen, and phosphate into the reef environment on nutrient dynamics.
|
From page 116... ...
Nevertheless, the suitability of the nutritional supplementation requires extensive evaluation with well-designed laboratory and aquarium-based experiments. Infrastructure A research and development phase would be needed to optimize coral diets.
|
From page 117... ...
. The infrastructure needed to deliver heterotrophic coral diets at the scale of reefs at this stage is unknown without extensive feasibility testing and development.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.