Ingestion of microplastic has limited impact on a marine larva.

There is increasing concern about the impacts of microplastics (<1 mm) on marine biota. Microplastics may be mistaken for food items and ingested by a wide variety of organisms. While the effects of ingesting microplastic have been explored for some adult organisms, there is poor understanding of the effects of microplastic ingestion on marine larvae. Here, we investigated the ingestion of polyethylene microspheres by larvae of the sea urchin, Tripneustes gratilla. Ingestion rates scaled with the concentration of microspheres. Ingestion rates were, however, reduced by biological fouling of microplastic and in the presence of phytoplankton food. T. gratilla larvae were able to egest microspheres from their stomach within hours of ingestion. A microsphere concentration far exceeding those recorded in the marine environment had a small nondose dependent effect on larval growth, but there was no significant effect on survival. In contrast, environmentally realistic concentrations appeared to have little effect. Overall, these results suggest that current levels of microplastic pollution in the oceans only pose a limited threat to T. gratilla and other marine invertebrate larvae, but further research is required on a broad range of species, trophic levels, and polymer types.

Moderate ocean warming mitigates, but more extreme warming exacerbates the impacts of zinc from engineered nanoparticles on a marine larva.

There is growing concern about the combined effects of multiple human-induced stressors on biodiversity. In particular, there are substantial knowledge gaps about the combined effects of existing stressors (e.g. pollution) and predicted environmental stress from climate change (e.g. ocean warming). We investigated the impacts of ocean warming and engineered nanoparticles (nano-zinc oxide, nZnO) on larvae of a cosmopolitan tropical sea urchin, Tripneustes gratilla. Larval T. gratilla were exposed to all combinations of three temperatures, 25, 27 and 29 °C (current SST and near-future predicted warming of +2 and + 4 °C) and six concentrations of nZnO (0, 0.001, 0.01, 0.1, 1 and 10 mg nZnO·L-1). These stressors had strong interactive effects on fertilization, gastrulation and normal development of 5 day old larvae. High concentrations of nZnO had a negative effect, but this impact was less pronounced for sea urchins reared at their preferred temperature of 27 °C compared to 25 or 29 °C. Larval growth was also impacted by combined stress of elevated temperature and nZnO. Subsequent measurement of the dissolution and aggregation of nZnO particles and the direct effect of Zn2+ ions on larvae, suggest the negative effects of nZnO on larval development and growth were most likely due to Zn2+ ions. Our results demonstrate that marine larvae may be more resilient to stressors at optimal temperatures and highlight the potential for ocean warming to exacerbate the effects of pollution on marine larvae.