Fig 1.
Photo of representatives for each diatom group based on morphological features.
No example is shown for group G13 (i.e. unknown diatoms) in this figure. Image source for G2: [33] modified, and for G11: [34] modified.
Table 1.
Diatom groups based on morphological features.
Fig 2.
Biofilm development over time.
The relative amount of biofilm found on PE (white) and biodegradable plastic (grey) after 15 and after 33 days of the experiment. Time 0 represents the polymer without biofilm. The error bars indicate the standard error. (A) Results of benthic samples (6 m water depth). (B) Results of pelagic samples (3 m water depth).
Table 2.
Biofilm amount in relation to plastic type, site and exposure time.
Fig 3.
Diatom abundance per treatment.
The number of diatoms found per square centimetre on PE (white) and biodegradable plastic (grey) is displayed after 15 and 33 days of the experiments. The error bars indicate the standard error. (A) Results of benthic samples (6 m water depth). (B) Results of pelagic samples (3 m water depth).
Table 3.
Diatom abundance in correlation to plastic type, site and exposure time.
Fig 4.
Detrended correspondence analysis (DCA) for the diatom community on PE and biodegradable plastic in the benthic (A) and in the pelagic zone (B).
Diatoms were categorised by morphology. Each data point represents a plastic sample, the distance between the data points shows the similarity of the diatom composition found on the sample. The smaller the distance, the more similar the composition was between the samples. Different symbols were used to group the samples by plastic type and sampling time. Around the centroid of all data points for these groups an ellipse indicating the 95% confidence interval of their standard error was drawn. If these ellipses do not overlap the groups are assumed to be significantly different (P ≤ 0.05).
Fig 5.
Amount of oxygen (µmol) produced per day per square centimetre of plastic surface (white for PE, grey for biodegradable plastic) after 15 days and after 33 days of the experiment. Time 0 represents the polymer without biofilm. The error bars indicate the standard error. (A) Results of benthic samples (6 m water depth). (B) Results of pelagic samples (3 m water depth).
Table 4.
Tensile properties (sigma and epsilon) for each treatment.
Fig 6.
SEM pictures of the plastic surface of PE samples following removal of the biofilm.
Each sample is displayed in two magnifications. (A) and (B) show untreated PE; (C) and (D) PE after 15 days; (E) and (F) PE after 33 days. Arrows in (F) mark fissures close to remains of the biofilm.
Fig 7.
SEM pictures of the plastic surface of biodegradable plastic samples following removal of the biofilm.
Each sample is displayed in two magnifications. (A) and (B) show untreated samples of biodegradable plastic; (C) and (D) of biodegradable plastic after 15 days; (E) and (F) of biodegradable plastic after 33 days. Arrows in (B) mark apparent starch particles and in (D) and (F) remaining holes.