No one knows exactly how much plastic there is in our oceans and we do not yet have enough data to understand the impacts in detail. But, we do know that plastic pollution detrimentally affects wildlife, climate, and even human health. To learn more we need to find new ways of studying plastic pollution in our oceans.
Every year, 11 million metric tonnes of plastic enter our oceans, equivalent to dumping one garbage truck full of plastic into the sea every minute of every day for an entire year. Therefore, that much plastic is bound to impact ocean ecosystems, especially when most of these plastic products break down and are ingested by marine wildlife.
The ocean is vast and covers about 71 percent of Earth’s surface, making it extremely difficult to study. Besides the large size of the ocean realm, most plastic does not float but sinks from the ocean’s surface to the seafloor, deep-sea currents distribute plastics in unknown patterns, and smaller plastic particles are ingested by marine life, making it even more challenging to quantify the amount of plastic.
For many years, biologists have used so-called bioindicators as proxies to answer research questions, where it was difficult to directly study an area or a species. In the case of plastic pollution in our oceans, researchers have also started to look into potential marine bioindicators to better understand the issue of plastic pollution in our oceans and answer open questions in the future.
What is a Bioindicator?
Bioindicators are living organisms, like plants, animals, and microbes, which can provide information on our environment’s quality, health, and biogeographic changes.
One example of an effective bio-indicator are lichens and moss. These species can monitor pollution and overall environmental health. Lichens and moss live on surfaces like trees, rocks, and soil and are extremely sensitive to toxins in the air. This is because they obtain their nutrients mainly from the air. They can survive in harsh conditions yet their abundance will signal changes in the ecosystem due to their persistent connection to the soil. The most sensitive lichens are shrubby and leafy while the most tolerant lichens are crusty in appearance. If the surrounding air is extremely polluted, the lichens will die until only green algae may be found. If the air is clean, shrubby, hairy and leafy lichens become abundant.
Bioindicators are not limited to land and can also be used in the marine environment. The criteria for choosing suitable marine species to serve as bioindicators, e.g., plastic pollution, include their distribution throughout the ocean and whether humans consume them. As a result, marine bioindicators tend to be higher up in the food chain and far-traveling species.
How to Find a Suitable Bioindicator to Assess Plastic Pollution in the Ocean
In a study done in the North Pacific Ocean, scientists from several research organizations, including the National Institute of Standards and Technology (NIST) and Stanford University, studied organisms as potential bioindicators to measure how much plastic exists in different ocean regions and help assess the overall health of the marine environment.
They analyzed and combined current scientific literature to first identify suitable marine species that could be used to monitor plastic pollution in the North Pacific Ocean and then assess the existing plastic pollution with these species.
The research focused on the North Pacific because of the presence of the Great Pacific Garbage Patch, making it one of the regions most heavily impacted by plastic pollution.
A total of 352 different marine species were evaluated, and 12 were identified as feasible bioindicators of plastic pollution in the North Pacific. These bioindicators ranged from the Pacific oyster and long-nosed lancetfish to the green sea turtle and black-footed albatross.
Putting the Bioindicators to the Test
Using the identified bioindicators as a proxy for plastic pollution, the scientists confirmed that the North Pacific is among the most polluted ocean regions globally. Roughly half of all examined fish and seabird specimens and more than three-quarters of sea turtles and bivalves in this region had consumed plastic.
In the future, tracking the health of the bioindicator species and the amount of plastic they ingest will help to assess the impacts of plastic pollution on wildlife and the effectiveness of mitigation actions in the region. Moreover, monitoring the health of the people consuming these species will identify potential health issues derived from plastic pollution.
Overall, the results will improve our understanding of plastic pollution, its possible impacts on wildlife and human health, and the effectiveness of plastic reduction measures.
Savoca et al. (2022). Towards a North Pacific Ocean long-term monitoring program for plastic pollution: A review and recommendations for plastic ingestion bioindicators. Environmental Pollution. 310: 119861. doi: 10.1016/j.envpol.2022.119861