The ocean, covering approximately 71% of Earth’s surface, provides multiple ecosystem services upon which humans depend. However, over the past decades, anthropogenic events are affecting the ocean’s fundamental balance. Firstly, climate change causes the temperature of the ocean to rise. These unnatural changes inevitably impact the ocean characteristics and, consequently, greatly alter ecosystem dynamics and services. Aquatic life exposed to this increase experiences thermal stress leading to detrimental effects on growth and reproduction. Another threat to the ocean and to marine organisms, is the accumulation of anthropogenic debris, in particular plastic, the most abundant debris reported in the marine environment. The development of more biodegradable plastics has been increasing, however, chemicals incorporated during the production process leach out of weathered debris causing toxicity in aquatic life. These factors lead to a knowledge gap in the understanding of the accurate effects of plastic and climate change on the marine environment. Marine invertebrates link primary producers to higher trophic levels. This is one of the reasons why assessing their effect on climate change and other environmental stressors are important. This study focused on the effect of di-lactide and dodecan-1-ol, two chemicals that leach out of poly-lactic acid, a bio-based plastic, in combination with an increased temperature on an individual and molecular level in the harpacticoid copepod Nitokra spinipes. On an individual level, ecotoxicological tests were performed to assess the single and combined effects of these stressors. Larval development rate, mortality, and reproduction were monitored during these tests. Exposure to di-lactide resulted in a delay in larval development but did not affect mortality. In a multiple stressor context, no effect of di-lactide and temperature was observed. Increasing concentrations of dodecan-1-ol increasingly delayed larval development and increased mortality. Individuals that were also subject to an increased temperature were more vulnerable to dodecan-1-ol exposure. An increased temperature significantly influenced the reproduction of N. spinipes, whereas di-lactide and dodecan-1-ol exposure did not seem to affect the reproduction. Before effects on an individual level are measurable, biomarkers are good indicators of stress. Results from a transcriptomic study indicate that heat shock protein 90 is upregulated after exposure to polylactic acid compounds and an increased temperature. However, results are preliminary and more testing of the intracellular pathway will be necessary to draw conclusions. Nonetheless, results indicate that di-lactide and dodecan-1-ol induce toxicity, and at an increased temperature, Nitokra spinipes becomes increasingly vulnerable. |
