Host and Symbionts in Pocillopora damicornis Larvae Display Different Transcriptomic Responses to Ocean Acidification and Warming

Abstract: As global ocean change progresses, reef-building corals and their early life history stages will rely on physiological plasticity to tolerate new environmental conditions. Larvae from brooding coral species contain algal symbionts upon release, which assist with the energy requirements of dispersal and metamorphosis. Global ocean change threatens the success of larval dispersal and settlement by challenging the performance of the larvae and of the symbiosis. In this study, larvae of the reef-building coral Pocillopora damicornis were exposed to elevated pCO2 and temperature to examine the performance of the coral and its symbionts in situ and better understand the mechanisms of physiological plasticity and stress tolerance in response to multiple stressors. We generated a de novo holobiont transcriptome containing coral host and algal symbiont transcripts and bioinformatically filtered the assembly into host and symbiont components for downstream analyses. Seventeen coral genes were differentially expressed in response to the combined effects of pCO2 and temperature. In the symbiont, 89 genes were differentially expressed in response to pCO2. Our results indicate that many of the whole-organism (holobiont) responses previously observed for P. damicornis larvae in scenarios of ocean acidification and warming may reflect the physiological capacity of larvae to cope with the environmental changes without expressing additional protective mechanisms. At the holobiont level, the results suggest that the responses of symbionts to future ocean conditions could play a large role in shaping success of coral larval stages.

Authors: E. B. Rivest, M. W. Kelly, M. B. DeBiasse, G. E. Hofmann


Year: 2018

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Frontiers in Marine Science 5:

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Interspecific Hybridization May Provide Novel Opportunities for Coral Reef Restoration

Abstract: Climate change and other anthropogenic disturbances have created an era characterized by the inability of most ecosystems to maintain their original, pristine states, the Anthropocene. Investigating new and innovative strategies that may facilitate ecosystem restoration is thus becoming increasingly important, particularly for coral reefs around the globe which are deteriorating at an alarming rate. The Great Barrier Reef (GBR) lost half its coral cover between 1985 and 2012, and experienced back-to-back heat-induced mass bleaching events and high coral mortality in 2016 and 2017. Here we investigate the efficacy of interspecific hybridization as a tool to develop coral stock with enhanced climate resilience. We crossed two Acropora species pairs from the GBR and examined several phenotypic traits over 28 weeks of exposure to ambient and elevated temperature and pCO2. While elevated temperature and pCO2 conditions negatively affected size and survival of both purebreds and hybrids, higher survival and larger recruit size were observed in some of the hybrid offspring groups under both ambient and elevated conditions. Further, interspecific hybrids had high fertilization rates, normal embryonic development, and similar Symbiodinium uptake and photochemical efficiency as purebred offspring. While the fitness of these hybrids in the field and their reproductive and backcrossing potential remain to be investigated, current findings provide proof-of-concept that interspecific hybridization may produce genotypes with enhanced climate resilience, and has the potential to increase the success of coral reef restoration initiatives.

Authors: Chan, W. Y., L. M. Peplow, P. Menéndez, A. A. Hoffmann, and M. J. H. van Oppen
Year: 2018
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Frontiers in Marine Science 5:

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Climate Change Promotes Parasitism In a Coral Symbiosis

Abstract: Coastal oceans are increasingly eutrophic, warm and acidic through the addition of anthropogenic nitrogen and carbon, respectively. Among the most sensitive taxa to these changes are scleractinian corals, which engineer the most biodiverse ecosystems on Earth. Corals’ sensitivity is a consequence of their evolutionary investment in symbiosis with the dinoflagellate alga, Symbiodinium. Together, the coral holobiont has dominated oligotrophic tropical marine habitats. However, warming destabilizes this association and reduces coral fitness. It has been theorized that, when reefs become warm and eutrophic, mutualistic Symbiodinium sequester more resources for their own growth, thus parasitizing their hosts of nutrition. Here, we tested the hypothesis that sub-bleaching temperature and excess nitrogen promotes symbiont parasitism by measuring respiration (costs) and the assimilation and translocation of both carbon (energy) and nitrogen (growth; both benefits) within Orbicella faveolata hosting one of two Symbiodiniumphylotypes using a dual stable isotope tracer incubation at ambient (26 °C) and sub-bleaching (31 °C) temperatures under elevated nitrate. Warming to 31 °C reduced holobiont net primary productivity (NPP) by 60% due to increased respiration which decreased host %carbon by 15% with no apparent cost to the symbiont. Concurrently, Symbiodinium carbon and nitrogen assimilation increased by 14 and 32%, respectively while increasing their mitotic index by 15%, whereas hosts did not gain a proportional increase in translocated photosynthates. We conclude that the disparity in benefits and costs to both partners is evidence of symbiont parasitism in the coral symbiosis and has major implications for the resilience of coral reefs under threat of global change.

Author: Baker, D. M., C.J. Freeman, J.C. Wong, M.L. Fogel, N. Knowlton
Year: 2018
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The ISME Journal. doi:10.1038/s41396-018-0046-8

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New Techniques for Coral Restoration in the Caribbean

Watch on YouTube

May 18, 2017

Hear experts from the Global Coral Restoration Project provide an overview of coral restoration efforts around the world and discuss current obstacles and potential solutions. This seminar kicks off an in-person workshop designed to foster exchange between practitioners working in the fields of coral science, restoration, aquaculture and marine resource management. Explore the seminar presentations and learn about coral restoration from the experts!

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Building Coral Reef Resilience Through Assisted Evolution

There is concern that elevated sea temperatures and ocean acidification may influence the resilience of coral reefs, inherently affecting their vital role of providing the structure which maintains ecosystem services around the world. This review explores the idea of artificially enhancing the ability of reef building organisms to handle stress and accelerate recovery after impact. While there is concern that artificially manipulated organisms may have a biological advantage over endemic species, corals are good candidates for assisted evolution. The authors advocate that stress exposure to natural stock, active modification of community composition of coral symbionts, selective breeding, and laboratory breeding of the symbionts all warrant research attention. As controversy continues to surround these ideas, it is important to consider that assisted evolution strategies such as these may increase the adaptive capacity of corals, perhaps allowing them to better respond to environmental and anthropogenic stressors more easily, in turn directly enhancing resilience.

Author: van Oppen, M.J.H., J.K. Oliver, H.M. Putnam, and R.D. Gates
Year: 2015
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Proceedings of the National Academy of Sciences 112(8): 2307-2313

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Coral Reefs On The Edge? Carbon Chemistry On Inshore Reefs Of The Great Barrier Reef

This study presents broad-scale carbon chemistry data from Great Barrier Reef (GBR) inshore coral reefs to test for regional and season differences between inorganic carbon system parameters in coastal waters. Spatial and temporal variations in sea surface carbon dioxide concentrations on a large-scale were examined to better understand the carbon cycle for predicting future increases in CO2. Data was collected from a large latitudinal range six times over a two-year period at 14 nearshore fringing reefs at islands in the GBR that experience terrestrial runoff. Carbon chemistry of inshore reefs was compared from smaller sample sets from mid- and outer-shelf reefs and historical data 18 and 30 years ago. Water samples were taken to analyze various parameters for oceanographic and water quality that serve as proxies for total alkalinity (TA) and dissolved inorganic carbon (DIC). Overall it was found that regional variability in carbon system parameters is relatively small; of variation in inshore reefs, the largest contributor was seasonal variation. Inshore reefs are subjected to elevated levels of partial pressure of CO2 (pCO2) as well as decreased light, increased sedimentation and higher nutrient levels compared to offshore reefs. The study found that the rate of increase of pCO2 in coral reef waters is increasing faster than in the atmosphere, likely due to other human-caused impacts on water quality, with higher values during the wet seasons. Thermodynamic effects contributed to higher aragonite saturation on inshore reefs and lower pCO2 than on offshore reefs, with land-based runoff contributing. The authors conclude that inshore GBR reefs could be more vulnerable to ocean acidification compared with offshore reefs.

Author: Uthicke, S., M. Furnas, and C. Lonborg
Year: 2014
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PLoS ONE 9(10): e109092. doi: 10.1371/journal.pone.0109092

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New and improved Network Forum

The Reef Resilience Network has launched a new and improved online discussion forum!

Now part of the Reef Resilience website, this interactive online community is a place where coral reef managers and practitioners from around the world can connect and share with others to better manage marine resources.

If you work to protect, manage, or promote coral reefs please join the conversation:

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New Reef Resilience Online Course Launched

The new online course Advanced Studies in Coral Reef Resilience is designed to provide coral reef managers and practitioners in-depth guidance on managing for resilience. This free course incorporates new science, case studies, and management practices described in the Reef Resilience Toolkit.

The course includes six modules that discuss local and global stressors affecting coral reefs, guidance for identifying coral reef resilience indicators, design principles for resilient MPA networks, methods for implementing resilience assessments, and important communication tools for managers. Course participants can choose to complete any or all lessons within course modules. Read more.

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Tool shows future predictions of bleaching and acidification

 Year when Degree Heating Weeks exceed 8 at least two times in the following decade under Representative Concentration Pathway 2.6.

Year when Degree Heating Weeks exceed 8 at least two times in the following decade under Representative Concentration Pathway 2.6.

A new Google Earth tool contains the most recent projections of coral bleaching and ocean acidification for all coral reef areas. The projections are based on climate models from the IPCC’s Fifth Assessment Report. Using this tool, managers can go to areas of interest and view:

  • The years by which two thermal stress levels known to cause bleaching are projected to occur twice per decade and annually;
  • Projected declines in aragonite saturation state as well as corresponding declines in calcification.

The use of the tool and images obtained from it will help coral reef managers to communicate about the threats posed to reefs by climate change with their colleagues, stakeholders and with policymakers.

The associated paper summarizes the results of the projections and highlights that under the fossil-fuel aggressive emissions scenario, there are no refugia from the onset of annual severe bleaching or the effects of ocean acidification. Under this scenario, by 2053, 90% of all coral reef areas will experience annual severe bleaching. There are opposite latitudinal gradients in these threats to reefs, meaning that areas projected to experience annual bleaching later are exposed to the effects of acidification for longer.

The Reef Resilience Program spoke with one of the authors of the report, Dr. Ruben van Hooidonk, about the relevance of this tool for coral reef managers.

Is there any good news coming from your findings?
Overall, the news is rather pessimistic, but the projections do show that some reefs will experience bleaching conditions annually 20 years or more later than others will. Many of these locations are of both local and global significance, such as the southern part of the Great Barrier Reef.

How do you see a coral reef manager using this tool?
The tool we have built allows access to projections that have coarse resolution (1 degree by 1 degree) and for long periods of time (decades).  Therefore, the results do not inform the targeting of management interventions like reducing pressures from fishing and scuba, though they do increase the impetus for such actions.  The primary purposes for which the projections were developed and made available are long term planning and outreach/awareness-raising.

What next steps do you think a coral reef manager should take after reading this article to address the impacts of ocean acidification and coral bleaching at their site?
Our article and the tool we have made available highlight the plight of coral reefs. Although a reef manager cannot easily address the global issues of increasing temperatures and acidification, managers can reduce local stressors that compound those associated with climate change and acidification. Perhaps more than any article before it, our work shows the urgency and necessity of local actions that support the natural resilience of reef systems.

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Managing coral reefs in the face of acidification

In “Preparing to manage coral reefs for ocean acidification: lessons from coral bleaching,” Dr. Elizabeth McLeod and her co-authors discuss how management strategies designed to address coral bleaching can be modified to address the impacts of ocean acidification. The authors note that while stabilizing CO2 emissions is the most critical step to address ocean acidification, it is beyond the scope of reef managers. They highlight the importance of management strategies to address ocean acidification including: spatial risk spreading; managing connectivity between source and sink reefs; and improved management of local-scale stressors to enhance reef resilience. Five research priorities are also identified to incorporate ocean acidification into conservation planning and management. Read the abstract or email for a copy of the article.

LizzieWe asked Dr. McLeod a few questions about acidification, and here’s what she said:

What coral reef region do you think will be impacted by ocean acidification first?
Some regions like the Great Barrier Reef, Coral Sea, and Caribbean Sea, are projected to have seriously low aragonite saturation more quickly than other important reef areas like those in the Central Pacific. The hard part about all of this is that these studies are looking at global patterns of ocean acidification and we now know that local processes can be even more important in affecting ocean chemistry than global processes. Reef-scale processes can either exacerbate or reduce the impacts of changing ocean chemistry, making it really hard to predict how one area will fare compared to another.

What next steps should a coral reef manager take after reading this article to address the impacts of ocean acidification at their site?
We need to reduce stressors as much as possible to support reef resilience. By keeping reefs healthy, they are better able to cope with the impacts of climate change and ocean acidification. Specifically, we need to reduce land-based
sources of pollution; this is particularly important for managing OA because nutrients like phosphorus and nitrogen can lower pH and aragonite saturation states in seawater. Managing herbivores is also critical because herbivores are really important for reef recovery following disturbance – keeping the algal growth in check so coral can settle and grow. The bottom line is that reducing stressors helps to support ecosystem health, and therefore, will help marine organisms focus their energy on growth, calcification, and reproduction as opposed to recovery from damage.

While doing research for this article, did you learn anything counter-intuitive or surprising about recommendations for managing for ocean acidification?
Yes. I was shocked by the large variations in pH and aragonite saturation states on some coral reefs. For example, on Heron Island Reef in the GBR, variations in pH and aragonite saturation state over one day were greater than the predicted changes in ocean chemistry globally by 2050. This is huge. This means that these local factors that can drive these reef-scale changes are really important!

Can you suggest further reading for managers interested in learning more about ocean acidification?
NOAA Pacific Marine Environmental Laboratory has a great website and Woods Hole Oceanographic Institution put together a really handy factsheet that has FAQs on ocean acidification. On this website you will find an overview of how ocean acidification works, and managing for ocean acidification.

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