The Coral and its Zooxanthellae: A Reflection on Human-Nature “Symbiosis”
Salem, OR
2020, Senior, Creative Writing
The first time I watched Marlin and Dory set out on their journey in the beloved Disney classic Finding Nemo was in eighth grade. At thirteen years, I was old enough to no longer be terrified by Bruce the Great White Shark but not quite old enough to recognize that the key players in a coral reef were not Nemo and Marlin, but instead the coral reef itself. Although it didn’t even dawn on my eighth-grade self that corals were alive, the colorful explosion of marine life that calls the reef home relies very much on the fact that corals are alive, and that they stay alive.
At the cornerstone of coral reef well-being is a humble, yet successful housing arrangement between coral polyps and zooxanthellae algae. Each individual polyp works cooperatively with zooxanthellae to recycle nutrients; their ultra-efficient partnership allows reef-building corals to grow to become “rainforests of the sea,” supporting a myriad of other strange and fascinating creatures, including our beloved fishy friends from Finding Nemo (Kolbert, 2014; Zandonella, 2016).
Although there is no jolly Mr. Ray taking his class of fishy students on a field trip (at least not that we know of!), marine organisms have evolved over the ages to form relationships with other species (University of Miami, n.d.). Nemo and his anemone home are one example; clownfish and anemones provide one another benefits in the form of protection and nutrients (National Geographic Society, 2019). Their relationship, like that between coral polyps and zooxanthellae, is considered mutualistic symbiosis—symbiosis is a relationship between two organisms, and mutualistic means it is a win-win partnership (NGS, 2019). Win-neutral and win-lose relationships are called commensalistic and parasitic, respectively (NGS, 2019). Everywhere you look, these relationships are at work in the reef, from a scuttling hermit crab with a giant triton’s shell on its back to barnacles clinging stubbornly onto swimming crabs (Public Broadcasting Service, 2001; NGS, 2019). Yet these individual symbiotic relationships between reef species still only represent a small fraction of the vast reef ecosystem and food web. This intricately complex food web lies in a sensitive balance; with each layer of the food web reliant on subsequent upper and lower trophic layers, a threat to one species could potentially result in highly disruptive ripple effects. From apex predators like sharks to primary producers like phytoplankton, each organism is critical to preserving the equilibrium of the marine food web.
Humans, too, are part of the food web. In the past, humans could simply be grouped among apex predators, hunting, fishing and gathering, helped along by our mighty opposable thumbs. But as human civilization advanced, our relationship with natural ecosystems has grown increasingly complex. Now we build houses, produce toxins, emit CO2, travel the globe, construct dams, grow crops, and generally interact with the environment in ways no other organism does. In a broad sense, we humans engage in two overarching “symbiotic” relationships: with nature and with technology.
The “symbiosis” between humankind and natural ecosystems is in many ways “parasitic” to nature, especially as we strengthen our “mutualism” with technology. Following the Industrial Revolution, the human-nature relationship grew increasingly toxic, so to speak, as we began pumping CO2 into the atmosphere and releasing pollutants and industrial wastes into the water and air. As the population grows and technologies advance, we continue to expand our reaches across the planet while disrupting wild habitats and introducing invasive species. Yet the fruits of technological innovation are certainly sweet. With heating and AC systems in our homes, we can stay at a comfortable temperature all year long. With cars, planes, and boats, we can travel and commute at unprecedented speeds. With industrialization, globalization, and the miraculous invention of the Internet, we can order food, clothing, furniture, and all manners of goods at the click of a button, and have them arrive on our doorstep within days. But as many of us humans become increasingly inundated with the comfort and contentment in our homes provided by technological advancement, other communities are crumbling.
In the ocean, the anthropogenic stressors of pollution, ocean acidification, and warming waters threaten marine communities large and small, from a single zooxanthellae-coral polyp housing unit to the entire reef ecosystem that they support. Excess nutrient pollution creates hypoxic and anoxic “dead zones” through large, and sometimes toxic, algae blooms (Howarth et al., 2011). Warming waters further contribute to deoxygenation, while also decreasing ventilation (mixing of waters) and disrupting “biological processes at cellular to ecosystem scales” (Reid, 2016). Ocean acidification, caused by the ocean absorbing nearly one-third of atmospheric CO2, diminishes the capacity of calcifying organisms like pteropods, reef-building corals, crustaceans, and mollusks to construct calcium carbonate exoskeletons (National Research Council of the National Academies, 2010). The combined stressors of eutrophication, ocean acidification, and warming are enormously detrimental to all ecosystems and coral reefs are no exception.
Ocean acidification directly inhibits reef-building corals’ growth through decreased calcification rates and dissolution of existing reef structures (NRCNA, 2010). At the same time, warming oceans target the mutualism with zooxanthellae that corals rely on to survive; in a study by Baker et al. (2018), increased water temperatures transform what was once a mutualistic relationship into one where zooxanthellae are effectively parasitic to the corals. The coral polyps then expel their former zooxanthellae compadres in bleaching events (Hoegh-Guldberg, 2010). While bleached corals can potentially recover their zooxanthellae partners, they will eventually die if placed under prolonged, warm temperatures (Hoegh-Guldberg, 2010). And when it dies, the colorful conglomeration of life that relies on the reef also disappears (Kolbert, 2014).
But human beings are by no means the villain in this story. Our potential to dramatically alter marine and terrestrial ecosystems with our technological advancements is indisputable. Yet at the same time, we can also launch tremendous efforts to try to save those same jeopardized communities. And that is what makes humankind truly remarkable. No other species in known history has researched the consequences of anthropogenic climate change on phytoplankton or gone deep-sea diving to study geothermal vents to predict effects of ocean acidification on marine biodiversity (Kolbert, 2014). To conserve critical coastal ecosystems, we have designated 6.35% of the ocean as Marine Protected Areas (MPAs) (International Union for Conservation of Nature, 2017). To promote sustainable fishing practices, we employ computer simulations to analyze the effects of fishing on specific fish stocks and the local marine ecosystem. We now apply cutting-edge technologies not against nature, but for nature, by developing more sustainable methods of living and providing scientific impetus for environmental policies.
And on a much smaller scale as individuals, we can gradually adjust our “symbiotic” relationships with technology and nature to adapt to the changes that we created. After all, as human-induced environmental effects have to come to show, food webs and symbioses are far from set in stone. If coral polyp-zooxanthellae mutualism can turn parasitic under stress caused by anthropogenic climate change and pollution, we too can change our relationship with nature for the better. In our homes, we turn down thermostats, switch out incandescent bulbs for LEDs, and limit plastic consumption. In our lifetimes, we seek out more sustainable alternatives to evolve the way we work, travel, eat, and buy. We alter our way of living so that zooxanthellae-coral polyp mutualism can once again thrive, and in the hope that stories like Finding Nemo, however whimsical, remain a viable reflection of life under the sea for generations to come.
Works Cited
Baker, D. M., Freeman, C. J., Wong, J. C., Fogel, M. L., & Knowlton, N. (2018). Climate change promotes parasitism in a coral symbiosis. The ISME Journal, 12(3), 921–930. doi: 10.1038/s41396-018-0046-8
Hoegh-Guldberg, O. (2010). Coral reef ecosystems and anthropogenic climate change. Regional Environmental Change, 11(S1), 215–227. doi: 10.1007/s10113-010-0189-2
Howarth, R., Chan, F., Conley, D. J., Garnier, J., Doney, S. C., Marino, R., & Billen, G. (2011). Coupled biogeochemical cycles: eutrophication and hypoxia in temperate estuaries and coastal marine ecosystems. Frontiers in Ecology and the Environment, 9(1), 18–26. doi: 10.1890/100008
International Union for Conservation of Nature. (2017). Marine protected areas and climate change. International Union for Conservation of Nature. Retrieved from https://www.iucn.org/resources/issues-briefs/marine-protected-areas-and-climate-change
Kolbert, E. (2015). The sixth extinction: An unnatural history. New York: Picador, Henry Holt and Company.
National Geographic Society (2019, April 17). Symbiosis: The Art of Living Together. Retrieved June 1, 2020, from www.nationalgeographic.org/article/symbiosis-art-living-together/
National Research Council of the National Academies. (2010). Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean. National Academies Press.
Public Broadcasting Service. (2001). Coral Reef Connections. Retrieved June 1, 2020, from www.pbs.org/wgbh/evolution/ survival/coral/partners.html
Reid, P. (2016). Ocean warming: setting the scene. In: Laffoley, D., & Baxter, J.M. (editors). (2016). Explaining ocean warming: Causes, scale, effects and consequences. Full report. Gland, Switzerland: IUCN. pp. University of Miami. (n.d.). Community Interactions: Coevolution and Symbiosis. Retrieved June 1, 2020, from http://www.bio.miami.edu/ecosummer/lectures/lec_coevolution.html
Zandonella, C. (2016, November 2). When corals met algae: Symbiotic relationship crucial to reef survival dates to the Triassic. Retrieved June 1, 2020, from www.princeton.edu/news/2016/11/02/when-corals-met-algae-symbiotic-relationship-crucial-reef-survival-dates-triassic
Reflection
Reflection
When thinking about our current climate crisis, I know all too well how easy it is to be overwhelmed by hopelessness. Words like “anoxic dead zones,” “harmful algae blooms,” and “ocean acidification” bring to mind almost apocalyptic images. But as daunting as our current situation may seem, I believe each individual can play an important part in helping to reduce anthropogenic climate change and to protect marine ecosystems. While researching for this paper, I found myself drawn to coral polyps; although each polyp is itself inconsequentially small, together with millions of other polyps they are able to form massive reefs that support a vast and biodiverse metropolis of marine life. Human civilization is not too unlike reef infrastructure. Each individual is integral in making up the bustling productivity and activity of our cities and towns. Likewise, we are all important in making the changes needed to protect our oceans whether by voting for politicians who prioritize environmental issues or by opting to buy local, organic produce. I am hopeful about our collective potential to mitigate anthropogenic effects on the environment and wanted to capture a sense of solidarity and cooperation in my paper. As such, I will continue to seek sustainable lifestyle choices and to amplify my voice in protecting our oceans through studies in environmental engineering. After all, our oceans have allowed us to live and thrive by keeping the Earth habitable. Now it is time for us to return the favor.