How Plastic Pollution Impacts The Coral Reef Ecosystem
Through National Geographic’s Planet or Plastic release in 2018, the world learned that only 9% of the roughly 8.3 billion metric tons of plastic created over the last six decades is recycled. The vast majority of the plastic is either accumulating in landfills or finding a home in various natural environments where it does not belong. The ocean, which makes up 71% of the planet, is one of the places where microplastics settle. Examples of these by-products include synthetic clothing fibers (like polyester, acrylic, and nylon), as well as plastic bottles and bags. Not only can marine life get caught in the plastic bags and fragments floating through the ocean, but habitats are destroyed and deadly particles ingested. Coral reefs, which serve as a habitat and source of food for 25% of the ocean, are one of the marine species at risk as plastic exposure can result in diseases, deterioration, and even death.
Jacqueline Padilla-Gamiño and Jeremy Axworthy, researchers at the University of Washington's School of Aquatic and Fishery Sciences, released a study in December of 2019 that focused on coral reefs’ consumption of microplastics[2]. The study took into account the multiple stressors corals face, such as warming water temperatures and ocean acidification. According to Axworthy and Padilla-Gamiño:
"Microplastics are not as simple as a life-or-death threat for corals — it's not that black or white. It's about total energy lost. If corals constantly are dealing with microplastics, it might not kill them, but there will be less energy for them to grow and to reproduce."
For their experiment, they collected two common species of coral off the east coast of Oahu, Hawaii. The species of coral were Montipora capitata and Pocillopora damicornis. The researchers divided the samples of coral into two groups, control and experiment. In the experiment group, they warmed the water to induce thermal stress and bleaching for three weeks. Then the team of researchers gave both the bleached and unbleached corals four different diets – 1) nothing, 2) microplastic only, 3) zooplankton and microplastic, and 4) a single type of zooplankton.
After dissecting the coral polyps, the researchers discovered that Pocillopora damicornis ingested significant amounts of microplastics when accompanied by zooplankton, but neither species consumed the microplastic particles alone.[2] Researchers were unsure as to why one species consumed microplastics that were accompanied by organic matter; they hypothesized that plastics with different chemical makeups could be more appetizing to corals during thermal stress events. A robust understanding of how coral species react to different plastics is critical for curbing the negative effects of plastic-based pollution in the ocean. The next step for the team is to investigate the physiology of corals exposed to microplastics over an extended time, and as of now, the results have yet to be released.
Cornell University conducted additional research, led by an international research group, and concluded that the trash ubiquitous throughout the world’s oceans amplifies the likelihood of coral disease from 4% to 89%.[1]Unfortunately, once a coral is disease-ridden, the damage has already been done and is irreversible. The Cornell research group surveyed 159 Pacific coral reefs surrounding Indonesia, Australia, Myanmar, and Thailand, to measure the impacts of plastic debris on tissue loss and disease. Each area experienced a different level of plastic pollution, with the highest concentration of 25.6 plastic items per 100 square meters near Indonesia.[3] Their data was divided into three broad classifications based on the complexity of the colonies. The classifications, from least complex to most complex, are 1) massive, 2) branching, and 3) tabular. The data showed that tabular coral morphologies are eight times more likely to maintain contact with plastic debris than massive coral morphologies, with extended contact correlating with a higher risk of disease.
Additionally, the study revealed that reef-building corals are susceptible to three types of diseases, taking into account that plastic serves as a vessel for pathogens.The first is skeletal eroding band (SEB), a disease caused by abrasions that expose the corals' tissue to invading pathogens. SEB eventually kills the reef, staining the coral's branches with dark gray/black bands and leaving behind a spotted region. The second disease, black band disease, is similar to skeletal eroding band and true to its name in that the afflicted corals develop a black band as the disease progresses. However, instead of leaving a spotted area of dead coral, black band disease leaves the reef completely bleached. According to Cornell researcher Joleah Lamb, the third disease, white band disease, occurs when “plastic debris [acts as] a marine motorhome for microbes.”[1] Foreign pathogens create a home within the corals that can lead to white syndrome, which presents as a white band that slowly kills the infected coral and changes it to the color of bone. When the coral reefs are negatively impacted and begin to lose tissue, weaken, or die, a chain reaction occurs that ripples throughout the ocean’s ecosystem. This ripple effect additionally impacts the livelihood of those in the fishing and ecotourism industry, as the reefs provide significant food sources, advances in medicine, and shoreline protection.
Researchers at the University of Delaware and alumni Danielle Dixon and Emily Ruhl noted the threats to coral reefs. They set out to see if 3-D printed coral could help revive and rebuild the coral reefs around the world. The experiment focused on the blue-green damselfish (Chromis viridis) located in the Indian and Pacific Oceans and the mustard hill corals (Porites aesteoides) commonly found in the Caribbean Sea.[5]
Four 3-D printed coral reefs were produced using low-cost filaments, polyester, cornstarch, or stainless steel powder and placed into a single fish tank filled with damselfish. Ruhl and Dixon noticed, through behavior analysis, that the damselfish behaved the same near artificial reefs as they did near natural reefs even though a natural coral skeleton was present, and made the following assessment:
“I thought the natural skeleton would elicit more docile behavior compared to 3D-printed objects, but then we realized the small reef fish did not care if the habitat was artificial or calcium carbonate; they just wanted protection."
The experiment also revealed that mustard hill larvae exhibited increased settlement rates on the 3D-printed surfaces; when given the choice between no settlement foundation and a 3D-printed one, they preferred the latter. Through the behavioral analyses of the damselfish and mustard hill larvae, research is beginning to show promising steps to rebuilding the coral reefs around the world. Furthermore, 3D-printed structures produced using biodegradable materials will naturally decay as the coral thrives, posing no risk to future growth and rehabilitation of our ocean ecosystems. [5]
While the implications of plastic pollution are known and reported, coral reef research is still in its infancy. Across the globe, scientists and researchers are testing hypotheses both in the field and in the lab to investigate a variety of questions – Why do some species of corals ingest microplastics, and others do not? Do additional stressors on corals — such as fluctuations in temperature, ocean acidification, and sedimentation — affect appetite and the ability to decipher what is organic matter and what is not? Will the long-term presence of plastic make coral more susceptible to disease, and if so, which ones? Overall, the impacts of the coral reef ecosystem examined through both scientific and pragmatic methods show that plastic pollution produced by developed and developing nations worldwide is taking a serious toll on the health of our oceans' ecosystems. Without the coral reefs, 25% of the marine life in the ocean loses its habitat or source of food, which will trickle through the ecosystems and eventually lead to shortages of fish for human consumption, recreational and commercial uses.
Citations
Cornell University. "A 'marine motorhome for microbes': Oceanic plastic trash conveys disease to coral reefs." ScienceDaily. ScienceDaily, 25 January 2018. www.sciencedaily.com/releases/2018/01/180125140848.htm.
Jeremy B. Axworthy, Jacqueline L. Padilla-Gamiño. Microplastics ingestion and heterotrophy in thermally stressed corals. Scientific Reports, 2019; 9 (1) DOI: 10.1038/s41598-019-54698-7
Lamb, Joleah B., et al. “Plastic Waste Associated with Disease on Coral Reefs.” Science, American Association for the Advancement of Science, 26 Jan. 2018, https://science.sciencemag.org/content/359/6374/460.
Parker, Laura. “A Whopping 91% of Plastic Isn't Recycled.” National Geographic, 20 Dec. 2018, www.nationalgeographic.com/news/2017/07/plastic-produced-recycling-waste-ocean-trash-debris-environment/#close.
University of Delaware. "3-D printed coral could help endangered reefs: Researchers find fish give 'fins up' to printed coral models." ScienceDaily. ScienceDaily, 16 October 2019. www.sciencedaily.com/releases/2019/10/191016124633.htm.
Willis, B.L. “Epidemiology of Skeletal Eroding Band on the Great Barrier Reef and the Role of Injury in the Initiation of This Widespread Coral Disease.” Coral Reefs, 2006, pp. 251–288., doi:10.1007/s00338-007-0317-8.