Coral Reefs and Phenotypic Plasticity: Responses to a Changing Climate

Introduction

Coral reefs are known as pristine locations, and the ability of the coral making them up to create environments supporting myriads of fish species is astounding. Comparisons between corals ability to create a niche for complex and diverse ecosystems has been compared to that of rain forests on land, with almost a third of marine fish being found, despite covering less than 1% of the ocean bed (Adey 1998). In fact, many of the species that live within these reefs owe survival to coral health (Komyakova et al 2013). However, the home of Nemo and Ariel has been under recent threat over the years, due to climate change and ocean acidification (Hoegh-Guldberg et a. 2007). Just this last year alone, the great barrier reef saw the worst coral bleaching, thanks to rising water temperatures (Griffith 2016).  While exploration of ways to change the impact we are having on corals, and therefore the impact on the reefs ecological webs as a whole, interest has also developed in what the corals responses to these changes in their environment have been (Putnam et al. 2016). The value of this data provides an extreme example of phenotypic plasticity, the ability of an organism to respond to its environmental conditions.

Phenotypic plasticity describes the potential of an organism to respond to different environments (Ghalambor et al. 2007). These responses are noted as changes in organism behavior or “form,” which in some cases may relate to an improvement in survivability in the new situation it may encounter (Forsman 2015). Examples can be found in humans, such as the difference you may see in identical twins who make actively different lifestyle choice; If one trains for a marathon every day, while the other spends most days catching up on all ten seasons of friends, you would notice a marked difference in athletic ability, and likely even individual temperament. These differences would be because of changes in the pressures put on the individual (amount of exercise), resulting down the line in changes in their genetic expression. However, the amount of responsiveness an individual can have is still limited by their gene repertoire they carry-for example, if you were to set a tree on fire, it would not be likely to respond in a way that could prevent its own demise. Therefore, knowing the capability of individual responses of coral would allow for a window to observing the short term impact, as climate change alters the environment it occupies.

The mechanism of these interactions stated earlier is regulation of gene expression via repressors and activators, as well as epigenetics,the amount a gene is expressed, relating to environmental factors that may limit or increase gene expression, results in ranges of  phenotypes across environments (Holliday 2006). Changes in gene expression can impart immediate changes to an organism’s ability to survive (Bird 2007). Having this ability to “change” based on given conditions gives various life greater leniency to expand it’s territory, and live in a semi-diverse environments; In the case of coral, it could perhaps act as a “buffer” to sudden changes brought into the ocean environment.

Putnam et al. (2016) designed their experiment to see differences in individual responses between clones of two species of coral Pocillopora damicornis and more environmentally robust Montipora capitata. These two species were selected, because of the formers sensitivities to changing environments, and the others consistent ability to survive in different climates. Their hypothesis was that the more sensitive (Pocillopora damicornis) coral would be more likely to show changes in metabolic profiles, calcification rates, and more variation in DNA methylation than the hardier coral.

To test this, they split selected coral from both species into 30 separate clones, and grew them in normal water conditions, with pH and temperature being the same as their native habitat. Then they altered the environment towards extreme conditions, for pH, carbon dioxide, and salinity. Following this, they measure what differences could be separated between these groups.

Results

Figure 3 (Putnam et al. 2016). (A) shows average growth of both coral species in each treatment over time; circle symbolizes Montipora capitata, triangle symbolizes Pocillopora damicornis. (B) Shows methylation pattern differences between species, and differences between treatments. Red symbolizes “High” treatment, blue represents natural conditions.

Differences were identified in the species ability to change in response to their environment, with Montipora having a higher degree of resilience than Pocillopora damicornis.Pocillopora also underwent higher degrees of calcification in response to acidification, as well showing stronger changes in metabolic profiles, and notable differences in DNA methylation. Based on this data, it is shown that individual coral can respond to changing environment, which may act as tool of survival in environments undergoing rapid change.

My Questions

Further research should be done on environmental contaminants, and impacts they are having on the coral habitat; presence of run off into the oceans of herbicides, pesticides and other environmental contaminants. Research should also be done to see if individuals who demonstrate phenotypic plasticity in among coral species are being selected for or if it relates to a lower fitness. Knowing that seasonality plays a role in some corals lives, the role that phenotypic plasticity may play in these species would also be curious to  and other chemical agents may also relate to how coral may behave and respond to its see.

Further Reading

  • Epigenetics and the influence of our genes: https://www.youtube.com/watch?v=JTBg6hqeuTg
  • Brown, B. E., & Cossins, A. R. (2011). The potential for temperature acclimatisation of reef corals in the face of climate change. Coral Reefs: An Ecosystem in Transition pp. 421-433 10.1007/978-94-007-0114-4_24
  • Fabricius, K.E., 2005. Effects of terrestrial runoff on the ecology of corals and coral reefs: review and synthesis. Marine pollution bulletin, 50(2), pp.125-146. 10.1016/j.marpolbul.2004.11.028
  • Hughes, T.P., Baird, A.H., Bellwood, D.R., Card, M., Connolly, S.R., Folke, C., Grosberg, R., Hoegh-Guldberg, O., Jackson, J.B.C., Kleypas, J. and Lough, J.M., 2003. Climate change, human impacts, and the resilience of coral reefs. science, 301(5635), pp.929-933. 10.1126/science.1085046
  • Parmesan, C., 2006. Ecological and evolutionary responses to recent climate change. Annu. Rev. Ecol. Evol. Syst., 37, pp.637-669. 10.1146/annurev.ecolsys.37.091305.110100
  • Whitman, D.W. and Ananthakrishnan, T.N. eds., 2009. Phenotypic plasticity of insects: mechanisms and consequences. Science Publishers. 10.1086/648172

References

  • Adey, W. H. 1998. Review—coral reefs: algal structured and mediated ecosystems in shallow, turbulent, alkaline waters. Journal of Phycology, 34(3), pp. 393-406.   10.1046/j.1529-8817.1998.340393.x
  • Bird, A., 2007. Perceptions of epigenetics. Nature, 447(7143), pp.396-398. 10.1038/nature05913
  • Forsman, A., 2015. Rethinking phenotypic plasticity and its consequences for individuals, populations and species. Heredity, 115(4), pp.276-284. 10.1038/hdy.2014.92
  • Ghalambor, C.K., McKay, J.K., Carroll, S.P. and Reznick, D.N., 2007. Adaptive versus non‐adaptive phenotypic plasticity and the potential for contemporary adaptation in new environments. Functional ecology, 21(3), pp.394-407. 10.1111/j.1365-2435.2007.01283.x
  • Griffith, H.2016. Great Barrier Reef suffered worst bleaching on record in 2016, report finds. Retrieved April 21, 2017, from http://www.bbc.com/news/world-australia-38127320
  • Hoegh-Guldberg, O., Mumby, P.J., Hooten, A.J., Steneck, R.S., Greenfield, P., Gomez, E., Harvell, C.D., Sale, P.F., Edwards, A.J., Caldeira, K. and Knowlton, N., 2007. Coral reefs under rapid climate change and ocean acidification. science, 318(5857), pp.1737-1742. 10.1126/science.1152509
  • Holliday, R., 2006. Epigenetics: a historical overview. Epigenetics, 1(2), pp.76- 10.4161/epi.1.2.2762
  • Putnam, H.M., Davidson, J.M. and Gates, R.D. 2016. Ocean acidification influences host DNA methylation and phenotypic plasticity in environmentally susceptible corals. Evolutionary Applications, 9(9), pp.1165-1178. 10.1111/eva.12408
  • Komyakova, V., Munday, P.L. and Jones, G.P. 2013. Relative importance of coral cover, habitat complexity and diversity in determining the structure of reef fish communities. PLoS One, 8(12), pp. 10.1371/journal.pone.0083178