| dc.description.abstract | The present study investigated the ingestion and egestion dynamics of four white textile microfibres (ca. 60 µm) in the marine copepod Calanus finmarchicus. This study is the first to expose aquatic invertebrates to microfibres of different chemical composition. A selection of synthetic and natural polymers were used: polyamide, polyester, treated wool, and untreated wool. Individual animals (young females) were incubated with microfibres (150 ml^-1) and microalgal feed (Rhodomonas baltica 7,500 cells ml^-1) during an uptake phase of 45 h, followed by a depuration phase of 96 h where the animals were only incubated with microalgal feed (total 141 h). Uniquely this experiment sampled the same copepods at 12 time points (4 h, 8 h, 16 h, 24 h, 45 h, 49 h, 53 h, 57 h, 69 h, 93 h, 117 h, 141 h) over the whole experiment, reducing noise from individual variation. A pulsed exposure was conducted where data was collected and media renewed at sampling points. Data on faecal pellet number, volume and microfibre content was collected to calculate variables related to faecal pellet production, microfibre ingestion and egestion, and ingestion of microalgae. There was no effect of microfibre exposure or composition on overall feeding rate of the copepods (p = 0.18). There was however a significant effect of microfibre composition on the ingestion of microfibres by C. finmarchicus (p < 0.001). The average ingestion rates of the four types of microfibre used in this experiment are: polyester = 24.2 microfibres hour^-1 copepod^-1, treated wool = 6.7 microfibres hour^-1 copepod^-1, untreated wool = 5.3 microfibres hour^-1 copepod^-1 polyamide = 1.7 microfibres hour^-1 copepod^-1. Due to small sample sizes, post hoc tests were not able to identify which microfibre type/s are ingested at significantly different rates than others. Ingestion rates indicate that polyester, the most common textile fibre, is ingested at a higher rate than the other microfibres tested. Chemical cues from the fibre or associated microbiota may be responsible for the selective ingestion observed herein. Alternatively, physiochemical parameters of the microfibres not tested here could affect dispersal in suspension, thereby affecting their availability. At the highest ingestion rate, microfibres occupied 12% of the faecal pellets by volume, suggesting a 12% reduction in microalgae intake. This decrease was not reflected in the volume of algae ingested by copepods. The retention time in the gut was comparable for all types of microfibres. Eighty percent of microfibres of all types were egested within the first 4 h of depuration. Less than 1 microfibre copepod^-1 persisted in the faecal pellets until the end of the experiment, possibly due to experimental conditions. Areas of further study include the mechanisms behind the selective ingestion of fibres observed herein, and the impact it has on copepod fitness. | |