Interactive effects of temperature and Bisphenol A on phytoplankton growth, community structure, and bioremediation capacity

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Meredith Theus, Julia Michaels, Tamara Layden and Samuel B. Fey, Department of Biology, Reed College, Portland, OR

Background/Question/Methods
Environmental contamination is a multifaceted issue that affects ecosystems, communities, and human society; however, certain organisms are capable of accumulating or metabolizing contaminants, reducing their negative impacts. Multiple species of phytoplankton are capable of removing Bisphenol A (BPA), a ubiquitous pollutant, from contaminated waterways. However, an understanding of the relationships between phytoplankton population growth, community structure, and the capacity of these populations and communities to remove BPA from the environment is currently underdeveloped. Here, we conduct laboratory experiments aimed at understanding how gradients of both temperature and BPA concentration influence phytoplankton population growth and community structure and subsequently investigate how these factors influence the capacity of phytoplankton to remove BPA from the environment. We exposed communities comprised of 3 species of freshwater algae (Chlorella vulgaris, Ankistrodesmus braunii, and Scenedesmus quadricauda) and isolates of each species to three BPA concentrations (0, 2, 13 mg/L) and three temperatures (18, 23, 27°C in the population and community level experiment; 18, 24, 28°C in the BPA determination experiment), monitoring community structure, population growth, and the change in BPA concentration over time (6 days).
Results/Conclusions
Temperature, BPA, and their interactions influenced phytoplankton population response with species specific patterns; however, growth was inhibited in all species under the highest BPA concentration. C. vulgaris growth was inhibited in all populations exposed to BPA. Contrastingly, A. braunii and S. quadricauda consistently grew at higher rates in low concentrations of BPA than in the absence of BPA. As temperature increased, growth rate increased in C. vulgaris and S quadricauda populations. Phytoplankton diversity (as measured by the Shannon Weiner Index) was influenced by BPA, temperature, and the interaction of these factors. Diversity decreased as BPA concentration increased and was significantly reduced under the highest BPA concentration and the highest temperature. Final BPA concentration was jointly influenced by species/community identity and starting BPA concentration with consistent BPA detection in the densest cultures, phytoplankton communities and C. vulgaris populations, cultured under the highest BPA concentration. These results underscore the importance of understanding the interactions among contaminants, environmental factors, and biological responses in determining how biological communities will be impacted by multiple environmental stressors and for developing ecologically informed remediation strategies.