Resilient amphipods: Gammarid predatory behaviour is unaffected by microplastic exposure and deoxygenation.

Microplastics are a ubiquitous and persistent form of pollution globally, with impacts cascading from the cellular to ecosystem level. However, there is a paucity in understanding interactions between microplastic pollution with other environmental stressors, and how these could affect ecological functions and services. Freshwater ecosystems are subject to microplastic input from anthropogenic activities (eg. wastewater), but are also simultaneously exposed to many other stressors, particularly reduced dissolved oxygen availability associated with climatic warming and pollutants, as well as biological invasions. Here, we employ the comparative functional response method (CFR; quantifying and comparing organism resource use as a function of resource density) to investigate the relative impact of different microplastic concentrations and oxygen regimes on predatory trophic interactions of a native and an invasive alien gammarid (Gammarus duebeni and Gammarus pulex). No significant effect on trophic interaction strengths was found from very high concentrations of microplastics (200 mp/L and 200,000 mp/L) or low oxygen (40 %) stressors on either species. Additionally, both gammarid species exhibited significant Type II functional responses, with attack rates and handling times not significantly affected by microplastics, oxygen or gammarid invasion status. Thus, both species showed resistance to the simultaneous effects of microplastics and deoxygenation in terms of feeding behaviour. Based on these findings, we suggest that the trophic function, in terms of predation rate, of Gammarus spp. may be sustained under acute bouts of microplastic pollution even in poorly­oxygenated waters. This is the first study to investigate microplastic and deoxygenation interactions and to find no evidence for an interaction on a key invertebrate ecosystem service. We argue that our CFR methods can help understand and predict the future ecological ramifications of microplastics and other stressors across taxa and habitats.

Ingestion of anthropogenic debris by migratory barnacle geese Branta leucopsis on a remote north-eastern Atlantic island.

Although seabirds are frequently used as sentinel species for anthropogenic pollution, the extent and impacts of synthetic debris ingestion remains poorly studied for many water bird species. Here, we assess ingestion of synthetic particles (≥0.5 mm) by barnacle geese, Branta leucopsis, wintering on a remote island. Faecal samples were collected over a period of four wintering seasons. In total, 71 individual samples were assessed, with 79% of samples displaying at least one debris particle (maximum lengths 0.5-5 mm) from anthropogenic sources. The recovered synthetic debris were identified as micro-fibres (n = 166) and micro-fragments (n = 165). The number of synthetic particles detected per sample was generally low at 4.7 ± 0.9, 43 (mean ± SE, maximum): micro-fibres 2.3 ± 0.3, 10; micro-fragments 2.3 ± 0.8, 40. Particle numbers detected per gram of faecal sample differed amongst wintering seasons. Our results suggest that non-marine water birds can frequently ingest low quantities of synthetic particles in remote coastal habitats.