LAUSR

Abstract Microplastic contamination is a growing threat facing marine ecosystems , of which a prominent source is the fibres from synthetic clothing. Ingestion and egestion (excretion) of microfibres , and whether these have short-term effects on behaviours such as feeding rate, have yet to be studied in many organisms, especially non-bivalve filter feeders . To determine if a common, filter feeding, intertidal invertebrate can ingest microfibres, we studied the acorn barnacle ( Balanus glandula Darwin 1854). We collected B. glandula from four locations near Bamfield, British Columbia, Canada, exposed half of them to a high concentration (~70,000 microfibres/L) of brightly coloured polyester microfibres for 24 h in unfiltered seawater (while the other half received a non-exposure treatment), and measured the feeding rates of the barnacles before and after the exposure. An average of 1.2 ± 1.9 fibres per barnacle were present in the gastrointestinal tracts of the plastic treatment group before depuration , and 0.3 ± 0.6 fibres per barnacle were found in the corresponding control group. Prior to depuration, 50% of the 20 barnacles in the plastic treatment ingested at least one microfibre, while a 15% ingestion rate was observed in the control group. There was no detectable short-term effect of microfibre ingestion on feeding rate. A 48-h post plastic exposure depuration period was used to evaluate whether microplastics were egested. No difference in egestion was found between those assessed directly after exposure and those that underwent depuration. Furthermore, a low depuration rate of 0.05 microfibres per 48 h suggests that barnacles may require longer than 48 h to egest microfibres. If representative, these results indicate that acorn barnacles ingested few microfibres even when exposed at very high concentrations, which supports the idea that they are at low risk for microplastic contamination and would not be a suitable indicator species.