Microplastics
Microplastics in Our Reef Ecosystems
Overview
There is a plastic paradox that scientists have studied for decades. Billions of tons of plastic are being dumped into the ocean each year, yet water quality reports lower concentrations coming out than what is going in [1]. Recent studies believe coral reefs to be sinks storing a large portion of this litter- microplastics [2].
Microplastics are plastic filaments less than 5mm in size. They are the result of decaying plastic in the ocean through photodegradation. The small size of these plastics makes them commonly mistaken for food for marine organisms, though they may also bind to coral structures through surface adhesion. This integration of microplastics into marine life causes circular adverse effects in the food chain, threatening the growth and health of marine organisms. However, continued research is working to reduce microplastic concentrations in the ocean to protect 25 percent of the world’s biodiversity inhabiting coral reefs [3].
Plastic waste is reportedly entering the ocean at a rate of 11 million metric tons per year and could expand to about 30 metric tons over the next 20 years. Ocean-wide research sheds light on how these microplastics are formed and distributed throughout our marine habitats. The impacts of microplastic distribution specifically on our reef ecosystems are still being explored through research unique to its own environment. Many possible solutions to plastics' effects on reefs are being tested and heard about through experimental research papers in relation to the removal of the microplastics and rehabilitation of reefs with new strategies and technologies.
Classifications of microplastics
Microplastics can be classified as one of two different types: primary and secondary. The primary microplastic description includes extremely small synthetic polymers derived by scientists and engineers. These polymers come from activities like sandblasting, the fabrication of synthetic clothes, and product maintenance. This classification also includes microbeads typically found in cosmetic products. Secondary microplastics are different forms of fragmented pieces of macro-plastics originating from environmental processes like photodegradation, hydrolysis, biodegradation, and thermo-oxidative degradation.
Main sources of microplastics
Plastic pollutants find their way into our oceans through several anthropogenic activities stemming from how they were formed. Domestic runoff powered by water flow from households, public facilities, and businesses is one of the simplest modes of transportation for these polymers that most of us are closest connected to. When cosmetics and other hygiene products which throughout their production have acquired microplastics, are rinsed off they enter our water system flowing out to the oceans or cycling through other product production and human consumption. Runoff carries microbeads and many fragments of large plastic trash from items properly or improperly disposed of.
Industrial plastic manufacturing fragmentation is a second large source introducing plastic in the form of pellets and resin powders from air blasting. Not only is there product waste due to inefficient manufacturing systems, but there is also waste in the form of simple degradation of material throughout the fabrication of the product.
Coastal fishing practices and aqua tourism source our marine microplastics from gear and single-use packaging for transporting goods and tools on boating trips which accumulate littered and forgotten. Across runoff, manufacturing, and marine activities the plastics collected are in varied shapes and sizes and stages of becoming microplastic if not already one. Due to the varying state, they settle in different areas throughout our oceans from juvenile habitats to reefs, open ocean, and deep-sea sectors.
Effects of Microplastic in Marine Ecosystems
Once entering the ocean, microplastics integrate themselves into coral reef communities through many methods. Each method is influenced by species-specific behavior, build, and the properties of the plastic. No matter the mode, microplastics impose threats for marine life health, development, and fitness.
The most direct form of microplastic integration is through active ingestion. As microplastics live in the ocean, they accumulate a biofilm layer that causes coral to mistake it for food (see figure 2 below). Coral with large polyps intake the microplastics. Fish similarly mistake the plastic bits as small organisms. Once ingested, the plastic reduces appetite of coral and fish which slowly lowers energy levels of the organisms which is needed to fight off disease [4].
While ingestion causes blockades in the digestive tracks of marine organisms, microplastics have also been found embedded in the skeletal matrix of coral. It is hypothesized this may be due to polyp growth over particles adhered to the exterior of the animal. Alternatively, the plastic may pass through the endoderm and calicoblastic layers of the animal and cemented into the skeleton as aragonite is laid down for growth. This rigorous integration causes concern for coral growth and tissue for housing zooxanthellae algae as an energy source [5].
The final most common mode of ingestion of microplastics is through passive surface adhesion. As plastic binds to the exterior of coral and other marine organisms, the organisms must overexert energy to remove these plastic bits. Additionally, for coral's zooxanthellae and other algae and plants, sunlight can be blocked, reducing photosynthetic performance and jeopardizing the energy capacity of organisms needed for survival [4].
It is important to note that microplastics do not just threaten their hosts, but so too threaten all organisms in the food web of the region. As fish eat plants or other fish containing microplastic, they also succumb to its health impacts, causing a vicious cycle of disease and reduced growth in a community [5]. Humans are no exception, as consuming fish with microplastic contents add to the five grams of plastic they consume each day- amounting to a credit card of plastic each week [6]. The figure below depicts this circulation of plastic in a marine community.
- ↑ Martin, Cecilia, et al. "Adhesion to Coral Surface as a Potential Sink for Marine Microplastics." Environmental Pollution, vol. 255, 2019. Crossref, https://doi.org/10.1016/j.envpol.2019.113281.
- ↑ Reichert, Jessica, et al. "Reef‐building Corals Act as Long‐term Sink for Microplastic." Global Change Biology, vol. 28, no. 1, 2021, pp. 33–45. Crossref, https://doi.org/10.1111/gcb.15920.
- ↑ "Tiny Plastics, Big Threat: How Are Microplastics Impacting Our Coral Reefs?" US EPA, 30 Nov. 2021, www.epa.gov/sciencematters/tiny-plastics-big-threat-how-are-microplastics-impacting-our-coral-reefs.
- ↑ 4.0 4.1 Chatterjee, Subhankar, and Shivika Sharma. "Microplastics in Our Oceans and Marine Health." Field Actions Science Reports, no. 19, 2019, pp. 54–61. Open Edition Journals, journals.openedition.org/factsreports/5257.
- ↑ 5.0 5.1 Pantos, Olga. "Microplastics: Impacts on Corals and Other Reef Organisms." Emerging Topics in Life Sciences, vol. 6, no. 1, 2022, pp. 81–93. Crossref, https://doi.org/10.1042/etls20210236.
- ↑ Kato, Brooke. "You're Eating a Credit Card's Worth of Plastic a Week - and It's Killing Your Gut." New York Post, 30 Mar. 2022, nypost.com/2022/03/30/youre-eating-a-credit-cards-worth-of-plastic-a-week-and-its-killing-your-gut.