Microplastics alter feeding strategies of a coral reef organism

Increasing marine microplastic pollution has detrimentally impacted organismal physiology and ecosystem functioning. While previous studies document negative effects of microplastics on coral reef animals, the potential responses of organisms such as Large Benthic Foraminifera (LBF) are largely unknown. Here, we document the impact of microplastics on heterotrophic feeding behavior of LBF. Specimens of Amphistegina gibbosa were incubated in three experimental treatments: (1) Artemia sp. nauplii only; (2) pristine microplastic particles only; (3) choice of nauplii and pristine microplastic. Feeding rates were observed 24 h after initiation of treatments. A separate experiment was conducted to compare the effect of conditioned vs. pristine microplastic. Our results indicate that A. gibbosa is able to selectively feed on Artemia, avoiding interactions with pristine microplastic. However, the presence of conditioned microplastic causes similar feeding interaction rates as with Artemia. This suggests microplastics with longer residence times may have a larger impact on facultative detritivores.

Methods
All experimental trials were performed in 12-well polystyrene plates. Three food choice treatment groups were defined: (1) Artemia sp. nauplii only (n = 10 nauplii in each replicate); (2) microplastic particles only (n = 10 microplastic particles in each replicate); (3) evenly split food choice of Artemia sp. nauplii and microplastic (n = 5 each). A total of 12 replicates of each treatment group were set up, and a randomized design was created to assign treatments to wells. A total of five specimens of A. gibbosa were placed into each well. Approximately 24 hours after the initiation of the experiment, feeding activity of A. gibbosa on nauplii and microplastic was assessed visually under a Leica binocular microscope, by counting the number of remaining nauplii and feeding attempts on microplastic particles and nauplii. For the purpose of this experiment, feeding on microplastic is defined as any physical interaction with the LBFs’ pseudopodia. Two trials were conducted, with a total of 24 replicates (12 per trial) in each treatment. None of the specimens were used in both trials. To ensure counting accuracy, an additional four counting controls per treatment were established, in which no LBF were placed in the well.