By Nhu-Y Tran

Millions of pounds of plastics enter the ocean, wreaking havoc on marine ecosystems. Marine ecosystems have had to evolve rapidly to survive these changes. If climate change and plastic pollution continue to increase at these rates, marine ecosystems may no longer be able to keep up with the changes. We need to enact change by taking steps to decrease the impacts of anthropogenic change on marine ecosystems.

Impacts of Climate Change & Urbanization

Marine debris, which is any solid material that accidentally or deliberately ends up in the ocean, can significantly impact marine ecosystems worldwide.  This includes injuring or killing wildlife, damaging habitats, and even changing the way these environments adapt and evolve to their presence (Alter et al., 2021; Galloway et al., 2017). However, marine ecosystems are incredibly diverse and resilient, allowing them to readily adapt and evolve in response to anthropogenic changes such as climate change, urbanization, and pollution.

Adaptations are traits that an individual organism has developed to improve its chances of survival, and evolution is adaptations or changes that occur across a population over several generations. Anthropogenic changes are a major concern because of their effect on the ability of species, and ecosystems as a whole, to adapt and evolve. Climate change has led to acidification and elevated temperatures in the ocean, and urbanization has led to habitat fragmentation and loss as well as increased pollution in and around coastal and marine environments (Alter et al., 2021; Audzijonyte et al., 2016; Medina et al., 2007; Paulus, 2021).

Evolving Tolerance: How Marine Life Copes with Stress

 In response to these stressors, many species have developed adaptations to better survive and thrive. Alter et al. (2021) and Audzijonyte et al. (2016) highlight the role that phenotypic plasticity, which are changes in the physical characteristics or presentation of an animal in response to their environment, plays in whether species are able to successfully adapt to the ever-changing marine environment. For example, many marine plants, fish, and invertebrates have evolved to become more tolerant, and in some cases even resistant, to the increased presence of toxic chemicals and metals such as copper (Alter et al., 2021; Oziolor et al., 2019). Water hyacinths (Eichhornia crassipes) have adapted to absorb, store, and filter metal and organic pollutants through their roots (De Laet et al., 2019). Gulf killifish (Fundulus grandis) in the Gulf of Mexico have evolved to become resistant to halogenated and polycyclic aromatic hydrocarbons, which are common industrial pollutants (Oziolor et al., 2019). Additionally, various gastropod species found in heavily polluted waters worldwide have been observed to have increased tolerance and/or resistance to metal and organic pollutants (Alter et al., 2021). In some cases, these pollutants or other stressors can be too much or occur too quickly for species to adapt, leading to them being replaced or removed altogether from that ecosystem (Medina et al., 2007).

Impacts of Plastics & Other Pollution 

In addition to climate change, another major anthropogenic change that has a significant impact on marine ecosystems is plastic pollution. With over 14 million tons of plastic entering the ocean each year, marine ecosystems have had no choice but to adapt and evolve to survive (IUCN, 2021). Plastic pollution comes in all shapes and sizes, each with a varying threat level to its surrounding ecosystem. Microplastics, which are plastic pieces less than 5mm long, are one of the biggest threats. This is because they can more easily absorb and release toxic chemicals and pollutants and can be ingested by organisms of practically any size (Feng et al., 2023; Galloway et al., 2017; Xu et al., 2021). 

Additionally, microplastics heavily impact the ability of marine ecosystems to adapt and evolve to the presence of plastics and other environmental stressors. Some studies have found that some benthic and microbial species, such as Brittle stars, mussels, and methanogenic and sulfate-metabolizing bacteria, had adapted to be able to digest microplastics and/or develop a resistance to the toxic chemicals that had been absorbed by the plastic (Feng et al., 2023; Galloway et al., 2017). This can be beneficial for those species’ longevity with the growing plastic problem. However, it could potentially leave them vulnerable to other environmental stressors by reducing their overall genetic diversity due to natural selection favouring individuals with certain traits, such as the ability to digest plastics or tolerate exposure to toxic chemicals (Medina et al., 2007). 

While microplastics are the most dangerous type of plastic pollution, other plastics also play a role in the evolution of marine ecosystems. In studies by Garcia-Gomez et al. (2021) and Haram et al. (2023), large plastics and other debris were observed to be used as rafts for various species. These “rafts” promoted the dispersal of invasive marine species, such as mussels, water hyacinths, and amphipods, which drastically disrupted the balance of whatever new ecosystem they arrived at. For example, food chains are often disrupted as these invasive species often lack any natural predators, allowing populations to thrive and consume all of the natural resources available.

Additionally, invasive species often carry and spread diseases that could wipe out native species (Garcia-Gomez et al., 2021). While rafts can promote the dispersal of species to new ecosystems, they can also promote isolation in others. In a study where invertebrate species were observed to be left adrift on rafts for extended periods, the isolated conditions occasionally triggered direct development or asexual reproduction in some species (Haram et al., 2023); this is a great example of the importance that phenotypic plasticity plays in the evolution and ultimate survival for many species. However, these processes can only occur so fast. If these issues continue to increase at their current rates, marine ecosystems may no longer be able to keep up.

Saving Our Seas

Anthropogenic activities pose a significant threat to marine ecosystems. Ocean acidification, increased temperatures, and habitat loss as a result of human-induced climate change and urbanization have forced marine species to adapt and evolve to survive rapidly. Plastics are also a major threat to marine environments. Microplastics readily absorb and release toxic chemicals which pose a risk to organisms of all sizes. Meanwhile, larger plastic debris can act as rafts, which can lead to the dispersal of invasive marine species, disruption of food chains, and spread of disease. 

As the primary source of marine debris, it’s up to us to take action to help save our seas. Some ways to do this include ditching disposables by saying no to single-use plastics and investing in reusable alternatives, spreading the word by talking to friends and family, and getting involved by supporting policies that reduce plastic use or joining organizations working to keep our oceans clean. Our choices, no matter how seemingly small or insignificant, matter and do make a difference. Let’s do our part to keep our oceans clean, healthy, and teeming with life!

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About The Author

Nhu-Y Tran is a graduate student with Project Dragonfly at Miami University in Oxford, Ohio in conjunction with the San Diego Zoo Wildlife Alliance.

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References

• Alter, S., Tariq, L., Creed, J., & Megafu, E. (2021). Evolutionary responses of marine organisms to urbanized seascapes. Evolutionary Applications, 14(1), 210-232.
• Audzijonyte, A., Fulton, E., Haddon, M., Helidoniotis, F., Hobday, A., Kuparinen, A., Morrongiello, J., Smith, A., Upston, J., & Waples, R. (2016). Trends and management implications of human-influenced life-history changes in marine ectotherms. Fish and Fisheries, 17(4), 1005-1028.
• De Laet, C., Matringe, T., Petit, E., & Grison, C. (2019). Eichhornia crassipes: A powerful bio-indicator for water pollution by emerging pollutants. Scientific Reports, 9(7326), 1-10.
• Feng, J., Li, C., Tang, L., Wu, X., Wang, Y., Yang, Z., Yuan, W., Sun, L., Hu, W., & Zhang, S. (2023). Tracing the century-long evolution of microplastics deposition in a cold seep. Advanced Science, 10(10), 1-13.
• Galloway, T., Cole, M., & Lewis, C. (2017). Interactions of microplastic debris throughout the marine ecosystem. Nature Ecology & Evolution, 1(0116), 1-8. 
• Garcia-Gomez, J., Garrigos, M., & Garrigos, J. (2021). Plastic as a vector of dispersion for marine species with invasive potential. A review. Frontiers in Ecology and Evolution, 9(629756), 1-28.
• Haram, L., Carlton, J., Centurioni, L., Choong, H., Cornwell, B., Crowley, M., Egger, M., Hafner, J., Hormann, V., Lebreton, L., Maximenko, N., McCuller, M., Murray, C., Par, J., Shcherbina, A., Wright, C., & Ruiz, G. (2023). Extent and reproduction of coastal species on plastic debris in the North Pacific Subtropical Gyre. Nature Ecology & Evolution, 7, 687-697.
• IUCN. (2021). Marine Plastic Pollution. IUCN. Retrieved from https://www.iucn.org/resources/issues-brief/marine-plastic-pollution
• Medina, M., Correa, J., & Barata, C. (2007). Micro-evolution due to pollution: Possible consequences for ecosystem responses to toxic stress. Chemosphere, 67(11), 2105-2114.
• Oziolor, E., Reid, N., Yair, S., Lee, K., Verploeg, S., Bruns, P., Shaw, J., Whitehead, A., & Matson, C. (2019). Adaptive introgression enables evolutionary rescue from extreme environmental pollution. Science, 364(6439), 455-457.
• Paulus, E. (2021). Shedding light on deep-sea biodiversity ⎯ A highly vulnerable habitat in the face of anthropogenic change. Frontiers in Global Change and the Future Ocean, 8(667048), 1-15.
• Xu, X., Hou, Y., Zhao, C., Shi, L., & Gong, Y. (2021). Research on cooperation mechanism of marine plastic waste management based on complex network evolutionary game. Marine Policy, 134(104774), 1-17.

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