Microplastics are ubiquitous in estuarine and marine environments. While their effects at organism level are currently being widely investigated, the effects at population-level, particularly in combination with other environmental stressors, are not yet clarified. The goal of this thesis was to assess the combined effects of microplastics and global warming (severe emissions scenario, SSP-8.5, IPCC) on benthic copepods, at both individual and population-level. To do so, Nitokra spinipes was exposed to microplastics, at control and increased water temperatures (+ 3 °C), using multiple polymer types (PLGA and PET, PVC, PS mixed) and concentrations (108 and 1010 particles m-3). Effects on individuals were assessed by identifying shifts in feeding and growth rates, as proxies for metabolism, and mortality. Our results showed that all N. spinipes treatments at 25 °C had higher mortality compared to 22 °C, increasing across MP concentrations. The LC50 at 25 °C was incorporated in a Dynamic Energy Budget Individual-Based Model to assess dose-response effects of microplastics on theoretical equilibrium population densities under projected warming conditions. At elevated temperature, the individual-level 14d-LC50 for mixed-microplastics was three-fold higher compared to the derived population-level LC50 (6.45 x 106 MPs m-3). This implies that the population dynamics of N. spinipes are more sensitive than observed short-term sublethal effects at an individual-level (adults). Our study demonstrates that the combined exposure of microplastic and elevated water temperature in a severe emissions scenario (SSP-8.5, IPCC) can induce increased mortality, and informs on the vulnerability of marine populations under current and future environmental conditions. |
