Low microalgae availability increases the ingestion rates and potential effects of microplastics on marine copepod Pseudodiaptomus annandalei

Microplastics have aroused great concern for their potential threats to marine organisms. This study investigated the interaction between three sizes of microplastics (0.5, 2, and 10 μm) and the marine copepod Pseudodiaptomus annandalei under two different microalgae concentrations (1 × 10³ and 1 × 10⁵ cells/mL). The results revealed that low microalgae supply increased microplastic ingestion through enhancing the encounter rates, and moreover increased the retention time of 0.5 μm microplastics. When the microalgae concentration was 1 × 10³ cells/mL, 0.5 μm microplastics could be observed in the copepods after depuration in clear seawater for 24 h, but almost totally excreted at 1 × 10⁵ cells/mL of microalgae. In addition, 0.5 μm microplastics induced significant effects on the ingestion of microalgae by P. annandalei both after 24 h of exposure and depuration. These results suggest that low microalgae availability may increase the ingestion and retention of microplastics in marine copepods, which might increase the ecological risk of microplastics.