Engineering the Corals of the Future

Contributed by Grant Wienker

-Featured Image by Gabrielle Cox

When you think of a coral reef dear reader, what do you see? Vast colonies of iridescent corals in all shapes and sizes, living together to create some of the most beautiful and diverse ecosystems on the planet? If so, then it should come as no surprise that these vast marine ecosystems collectively host a quarter of the known life of the ocean, and produce an abundance of natural capital for the coastal economies they neighbor. However, what isn’t included in that beautiful imagery are the devastating effects climate change is having on these atlantian paradises. As our climate grows warmer, consecutive bleaching events have caused large coral die-offs. A bleaching event is when coral expels its symbiotic algae and loses its pigment, taking on a bleached appearance. Due to the frequency of these bleaching events, the Environmental Protection Agency has claimed that coral reefs are a critically endangered species. This is further backed by The World Counts stating around 45.8% of the world’s corals are alive at the moment.¹

OUR STUDIES ON CORAL REEFS ARE DATED

The majority of research on coral has an antiquated focus on preventative measures as seen by the common rhetoric of protecting reefs before climate change occurs, opposed to mitigation or adaptation-based approaches in the wake of climate change. The results of a study done by Adrien and Linwood, showed that conservation methods are vastly underrepresented in the databases Web of Science and Scopus.² Within the study, the sampled articles on coral reefs were separated into four groups based on their language; protect, mitigate, repair, and adapt. Adrien and Linwood found that the ‘protect’ category, especially in marine protected areas (MPA), was the most cited strategy and showed that the distribution of studies for each category isn’t equally represented. With fields of research in long-term coral conservation being underrepresented, Adrien and Linwood discovered a disparity in information on coral. With this knowledge, it is possible to change the species’ future. However, there needs to be some motivation for scientists to actually go out and record the data we need. A deeper look into the evolutionary biology of coral reveals that the adaptations developed millions of years ago to help with climate change, which leads to the question: If coral has already developed ways to battle naturally changing environmental factors and has been doing so for millions of years, why is coral struggling so much right now?

CORAL HAS BEEN PUTTING UP A FIGHT

In the International Panel on Climate Change Summary in 2014, it was stated that the most noticeable effects of climate change in the ocean are acidification and rising temperatures.³ Acidification occurs when the ocean absorbs carbon dioxide from the atmosphere. Once absorbed, it reacts with seawater to make carbonic acid(H₂CO₃). The ocean acts as a buffer for this acid, and as the hydrogen ions dissociate, bicarbonate(HCO^-3) is formed, decreasing overall pH. This causes problems for hard corals as they have calcium carbonate(CaCO₃) shells, and as the ocean’s pH level decreases individual hydrogen ions in the water bind with the carbonate(CO₃^-2) from the coral’s exoskeleton, again creating bicarbonate. This can have a range of effects from stunted coral growth rates, to actually dissolving coral exoskeletons. This alone creates an unhealthy environment that inhibits coral’s survival, but when paired with rising ocean temperatures, it creates lethal environments. Research conducted by The National Oceanic and Atmospheric Administration(NOAA) found that any severe change or variation in sea temperature trends causes coral to bleach.⁴ Bleaching itself is normal, as bleaching events cause coral to expel their symbiotic zooxanthellae algae, allowing for a widespread re-configuration of coral algae pairings, which quickly changes the genetic make-up of an entire reef. But the effects of climate change have caused these events to become more frequent and the mortality rate of coral has increased dramatically over the past couple of years.

However, corals undergo bleaching events at differing ocean temperatures, indicating that there is some distribution of heat resistance throughout a reef’s population. The presence of bleaching-resistant species of coral, along with the fact that coral can recombine with different types of symbiotic algae after bleaching events, lead Andrew Baker to believe that this could make way for major conservational advancements in the coral community when they stated, “…evidence exists indicating that diverse symbionts can significantly buffer the effects of climate change…”.⁵ Baker thought the fact that coral can host multiple symbionts throughout its lifetime is an adaptation for passive genetic recombination. Some corals have found other novel ways of coping with stress. According to Cropp et al. 2018, there is evidence of corals on Heron Island releasing aerosols, or fine liquid droplets, into the air to locally mitigate the effects of sunlight.⁶ It was thought to be done in an effort to reduce solar irradiance or electromagnetic power per square unit area, as a natural defense mechanism against harsh sunlight because light aerosols, as opposed to dark aerosols, have the opposite effect of most greenhouse gasses. They reflect sunlight away from the earth and produce a net cooling effect on the area. In their study, Cropp et al.(2018) used “daily measurements of atmospheric optical depth for fine-mode aerosols” to calculate the amounts of aerosols being produced from the corals of Heron Island.⁶ Afterward, an index was made to map the factors that cause coral stress during times of high solar irradiance with water depth, water clarity, and sea surface irradiance were found to have the most impact on aerosol production.

BUT CORALS CAN’T KEEP UP

Currently, the two main adaptations coral has evolved to fight climate change, symbiont recombination and aerosol release, are not enough to keep the species alive in rising ocean temperatures as stated by studies conducted by Baker and Cropp et al.^5,6 Both of these adaptations to climate change show that coral has evolved methods to battle a naturally changing climate. A team of researchers from a separate study agreed and supported these ideas by explaining that, “corals evolved in the Middle Triassic and have adapted and evolved to survive over tens of thousands of years”.⁷ This, along with the results from the research conducted by Baker and Cropp et al., provides ample evidence for coral’s ability to adapt to changing environments. Kubicek and colleagues took coral adaptations and simulated a model to measure coral’s defense mechanisms versus projected global warming. In modeling their simulation they wrote, “We populated the model with an array of massive and branching species with different combinations of these three traits—growth rate, thermal stress tolerance, and competitiveness with neighbors—, in which pairs of species, one of each morphology, share the same trait combinations”.⁷ This was done to maximize the genetic diversity of the model in order to get the best results. After simulating 90 years of evolution, Kubicek and colleagues reported that a temperature increase of 2°C (4.5RCP) left only 5 of the 200 initial species alive.⁷ Something to note is the simulation was based on a carbon dioxide representative concentration pathway(RCP) provided by the IPCC. Every time the IPCC meets for a climate conference they give potential global warming scenarios based on the rate of carbon released into the atmosphere, with a higher number indicating a scarier outcome. The 4.5 RCP is the second most conservative representation given, and yet still more than 90% of coral species are projected to go extinct with this model. In an alternate scenario presented in the same study, if the ocean temperature increased by 3°C or more, bleaching and mortality events would become so frequent and severe that none of the simulated species survived longer than 50–60 years”.⁷
While the simulations predict coral extinction, a study done by Campbell and colleagues suggests that coral could survive through assisted evolution. Assisted evolution is the process by which species are genetically altered to successfully adapt to an anthropogenically changing climate and for coral, this means selecting species that exhibit desirable traits for combating climate change. In their study, Campbell furthered the case for conservation biology by successfully growing modified coral that supported local species through the successful restoration of reef habitat in Pulau Weh, Indonesia.⁸ The ability to repopulate barren reefs gives hope for the survival of coral in the future because these evolved generations grow in 20-30 years, well within the window predicted by Kubicek and colleagues.

WHAT THIS MEANS FOR HUMANS

While assisted evolution has the potential to save coral, it’s no guarantee. A future without coral is unacceptable as these reefs provide a multitude of services to humans that are taken for granted. NOAA states that coral reefs provide physical protection for coastal communities by buffering waves, storms, and floods.⁴ Not only does coral protect coastal communities, but it also provides them with economic capital in natural resources and the growing tourism industry. An estimate by Conservation International claimed that the total net benefit per year of the world’s coral reefs is $29.8 billion with tourism and recreation accounting for $9.6 billion of this amount, coastal protection for $9.0 billion, fisheries for $5.7 billion, and biodiversity for $5.5 billion.⁹ If coral were to go extinct, the steady supply of income and protection they provide would cease to exist, crippling coastal communities in the future. These communities wouldn’t be the only ones affected, as coral is a founder species and provides a large amount of biodiversity for the ocean. A founder species is one that can create the ecosystem it lives in. Coral builds the sprawling reefs seen today by slowly absorbing carbonate ions from the ocean over time. The carbonate that is taken this way will then become the exoskeleton of the coral as it develops. But this process takes time, as NOAA stated that reefs can take up to 10,000 years to grow to the sizes we see today, with the Great Barrier Reef as an example, as it is about the same area as the country of Italy.⁴

A common counter-argument to the conservation of coral states if one degree Celcius is projected to change the outcome of the survival of this species, then maybe they aren’t supposed to survive. This perspective is based on a much longer timescale than we are used to, as it looks into the complete history of life on earth. Over earth’s history, there have been 4-5 major extinction events that have occurred naturally. After each of these extinctions, there are periods of great diversification for the species remaining because they are able to utilize all the previously shared resources. This is what’s known as adaptive radiation, or rapid diversification of a species over short periods of time. The counter-argument takes this approach when considering the conservation of coral: If coral, a massive provider of genetic diversity in the ocean and a keystone species, suddenly dies out, there will be large amounts of newly freed resources for other species to exploit, allowing for adaptive radiation of new species, filling the niche in place of coral.
While this way of thinking is biologically sound, humans live in a much shorter timescale and there are several consequences associated with coral extinction that would cause major changes to the world we live in. With coral providing a habitat for a quarter of the known life in the ocean, it goes without saying that some of the species it provides for are likely to face extinction as well. This could cause a trophic cascade that decimates the majority of life in the ocean, as it would result in the global food web becoming incomplete. For coral, the evidence for conservation should be enough to constitute human involvement on its own. Despite our challenges, research has shown that with enough public funding new corals can be speciated through assisted evolution that could survive in future ocean climates for our future generations.

References

1. The World Counts. (n.d.). Coral reef destruction. Retrieved from https://www.theworldcounts.com/counters/ocean_ecosystem_facts/coral_reef_destruction_facts
2. Adrien, C., Linwoon, P. (2018, March). Management strategies for coral reefs and people under global environmental change: 25 years of scientific research. Journal of Environmental Management. 209(1), 462-474. Retrieved from https://www.sciencedirect.com/science/article/pii/S0301479717312318?via%3Dihub
3. IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.
4. NOAA. (2018, June 25). What is coral bleaching?. Retrieved from https://oceanservice.noaa.gov/facts/coral_bleach.html
5. Baker, A. (2003, August 6). Flexibility and specificity in coral-agal symbiosis: Diversity, Ecology, and Biogeography of Symbiodinium. Annu. Rev. Ecol. Evol. Syst. 2003. 34:661-689 Retrieved from https://www.annualreviews.org/doi/pdf/10.1146/annurev.ecolsys.34.011802.132417
6. Cropp, R., Gabric, A., Dien, v. T., Jones, G., Swan, H., & Butler, H. (2018, February 3). Coral reef aerosol emissions in response to irradiance stress in the great barrier reef, Australia. Ambio, 47(6), 671-681. Retrieved from http://dx.doi.org/10.1007/s13280-018-1018-y
7. Kubicek, A., Breckling, B., Hoegh-Guldberg, O., & Reuter, H. (2019). Climate change drives trait-shifts in coral reef communities. Scientific reports, 9(1), 3721. doi:10.1038/s41598-019-38962-4
8. Campbell, S. J., Ferguson, K., Keyse, J., Rudi, E., Riedel, A., & Baird A. H. (2012). The role of habitat creation in coral reef conservation: a case study from Aceh, Indonesia. Oryx, 46(4), 501-507. Retrieved from https://www.cambridge.org/core/journals/oryx/article/role-of-habitat-creation-in-coral-reef-conservation-a-case-study-from-aceh-indonesia/89E1E6212014368B15E E54EC9144C67D
9. Conservation International. 2008. Economic Values of Coral Reefs, Mangroves, and Seagrasses: A Global Compilation. Center for Applied Biodiversity Science, Conservation International, Arlington, VA, USA.