Marine plastic debris emits a keystone infochemical for olfactory foraging seabirds

Abstract

Plastic debris is ingested by hundreds of species of organisms, from zooplankton to baleen whales, but how such a diversity of consumers can mistake plastic for their natural prey is largely unknown. The sensory mechanisms underlying plastic detection and consumption have rarely been examined within the context of sensory signals driving marine food web dynamics. We demonstrate experimentally that marine-seasoned microplastics produce a dimethyl sulfide (DMS) signature that is also a keystone odorant for natural trophic interactions. We further demonstrate a positive relationship between DMS responsiveness and plastic ingestion frequency using procellariiform seabirds as a model taxonomic group. Together, these results suggest that plastic debris emits the scent of a marine infochemical, creating an olfactory trap for susceptible marine wildlife.

Keywords: Chemical ecology; conservation biology; dimethyl sulfide; foraging ecology; marine pollution; plastic debris; sensory ecology.

Fig. 1. DMS concentration in plastic debris headspace.

(A) DMS was not detected on any of the virgin plastic samples tested (n = 10 samples each for HDPE, LDPE, and PP, N = 30 total). (B) DMS was detected on every plastic sample after marine exposure (n = 12 bags of each plastic type; each bag subsampled five times). Box plots illustrate DMS concentrations on marine-seasoned plastic of each plastic type across sites (HPDE = 8.31 ± 2.25 μg of DMS per gram of plastic; LDPE = 8.90 ± 1.34 μg of DMS per gram of plastic; PP = 9.56 ± 2.33 μg of DMS per gram of plastic). Points represent each bag’s average DMS quantification; the error bars represent the SE of the five subsamples of each bag. Site averages by plastic type are as follows: for BML, x̄_HDPE = 13.45 ± 2.41 μg g⁻¹, x̄_LDPE = 11.76 ± 1.65 μg g⁻¹, and x̄_PP = 4.99 ± 0.98 μg g⁻¹; for HMS, x̄_HDPE = 3.16 ± 1.07 μg g⁻¹, x̄_LDPE = 6.05 ± 1.39 μg g⁻¹, and x̄_PP = 14.13 ± 2.33 μg g⁻¹.

Fig. 2. Effects of DMS responsiveness and nesting behavior on plastic ingestion in procellariiform seabirds.

(A) Maximum likelihood estimate (±SEM) of the DMS-responsive and non–DMS-responsive species groups, illustrating a significantly higher frequency of plastic debris ingestion in DMS-responsive species (binomial GLMM, P < 0.0001). (B) Maximum likelihood estimate (±SEM) of burrow- and surface-nesting species groups, illustrating a significantly higher frequency of plastic ingestion in burrow-nesting species (binomial GLMM, P < 0.05). Burrow-nesting behavior is used here as a proxy for DMS responsiveness.

Fig. 3. Plastic ingestion and DMS responsiveness among procellariiform seabirds.

Colored circles and horizontal lines represent the mean and 95% CIs for each species’ model-predicted plastic ingestion prevalence. Vertical dashed lines are model-predicted mean plastic ingestion frequency for each group (DMS-responsive and non–DMS-responsive). Vertical dotted lines represent the 95% CIs of the plastic ingestion frequency for each group.

Fig. 4. Relationship of plastic ingestion and nesting behavior.

Colored circles and horizontal lines represent the mean and 95% CIs for each species’ model-predicted plastic ingestion frequency. Vertical dashed lines are model-predicted mean plastic ingestion frequency for each group (burrow- and surface-nesting). Vertical dotted lines represent the 95% CIs of the plastic ingestion frequency for each group.