UC San Diego Study: Petroleum Plastic Pollution May Amplify Harmful Algal Blooms

A recent study by the University of California San Diego (UC San Diego) suggests that petroleum-based plastic pollution may amplify harmful algal blooms (HABs) by reducing the populations of animals that typically consume algae. While excessive nutrient input from land sources has traditionally been identified as a cause of HABs, this research indicates an additional factor contributing to these events. HABs have been observed globally and linked to marine species deaths, including a nine-month toxic bloom in Southern Australia.

Understanding Harmful Algal Blooms (HABs)

Harmful algal blooms (HABs) are concentrations of algae that can produce toxins, leading to adverse environmental and health impacts. Historically, these blooms have been primarily attributed to elevated nutrient levels in aquatic environments, often stemming from agricultural runoff and waste discharge.

Plastic pollution, including microplastics, is widespread globally, detected in various ecosystems and biological systems.

UC San Diego Study: Methodology and Scope

Researchers from UC San Diego's Department of Ecology, Behavior and Evolution and Department of Chemistry and Biochemistry conducted a three-month study involving 30 experimental pond ecosystems. The study aimed to compare the environmental effects of conventional fossil fuel-based polyurethane plastic with a recently developed biodegradable plastic.

The biodegradable material included sustainable plastic developed in UC San Diego laboratories and commercialized by the university spinoff company, Algenesis.

Professor Jonathan Shurin, the study's senior author, noted that while nutrient pollution contributes to algae blooms, the study indicates that "some of the algae blooms that we see around the world may also be due in part to the effects of plastic on the animals that normally control algae."

Key Findings: The "Top-Down" Effect of Plastic

The study identified "top-down" effects caused by fossil fuel plastics, leading to a decline in animals that consume algae. The experiments showed that microplastics alter microbial communities, including algae and bacteria.

Specific observations included:

• Zooplankton Decline: In tanks containing fossil fuel plastic, zooplankton populations—tiny aquatic animals that graze on algae and serve as a food source for fish—decreased rapidly.
• Algae Increase: The reduction in zooplankton grazers corresponded with a swift increase in algae concentrations within these tanks.
• Bioplastic Impact: Tanks tested with biologically based plastics showed a significantly smaller impact on zooplankton and other members of the ecosystem.
• Differential Effects: Scott Morton, the study's first author, stated that petroleum plastic appeared to have a strong negative effect on zooplankton populations, either causing death or reducing reproduction, which then led to increased algal blooms. Bioplastic did not exhibit the same effect, resulting in more zooplankton and fewer algal blooms in those systems.
• Bacterial Communities: Researchers also documented the emergence of distinct bacterial communities in the presence of plastic, though the specific cause for this remains under investigation.

The study concluded that microplastics, particularly those derived from petroleum, may destabilize microbial community structure and function, thereby favoring algal blooms.

Implications and Future Directions

While the full ecological impacts of microplastics are still being studied, the authors suggest that transitioning to a biodegradable plastics economy could potentially mitigate the environmental effects of plastics in aquatic ecosystems.

Co-author Professor Michael Burkart's group has developed bio-based plastics designed to biodegrade in natural environments. Professor Burkart is also the founder and holds an equity position in Algenesis Materials, a company commercializing renewable materials.

Researchers are continuing to explore these findings, including testing various types of biodegradable plastics and "living plastic" that incorporates bacterial spores intended to break down the material.