Biodegradable Plastics in the Marine Environment: Comparative Analyses of Bacterial Biofilms, Macroinvertebrate Colonization, and Degradation Patterns

Floating debris in the ocean recruits microbes and marine invertebrates to its surface, resulting in rafting communities. As biodegradable plastics increase in prevalence as alternatives to petroleum-based plastics, their properties may impact the dynamics of rafting communities by influencing the composition of bacterial biofilms and attached invertebrates. We compared attached biofouling communities of bacteria and marine invertebrates on biodegradable surfaces and nonbiodegradable petroleum-based plastics and naturally occurring substrata. Six surface types: polypropylene plastic (PP), polystyrene (PS), polylactic acid plastic (PLA), polyhydroxyalkanoates plastic (PHA), maple wood veneer, and propagules of the mangrove Rhizophora mangle, were examined to determine if plastic type affected biofilm composition on the surfaces and their degradation patterns. Biofilm analyses were conducted at twelve weeks, and degradation analyses were conducted at twenty-two weeks of immersion. Using digital image analysis, 16S rRNA sequencing, and metagenomic analyses, we found that microbial biofilms, marine invertebrate inhabitants, and degradation patterns differed across the various substrate types tested. Microbial communities on PLA were more similar to those on the two non-biodegradable plastics, while communities on PLA were more like those on the natural substrata. The biodegradable PLA showed signs of degradation within 22 weeks of immersion, suggesting that biodegradable plastics behave variably in the natural environment. Results of this study bring forth the importance of designing biodegradable plastics with careful consideration of the environmental conditions in which they are likely to persist.