Polymer type and UV-treatment influence the first week of biofilm development in Caribbean sublittoral waters

Marine plastic pollution has increased exponentially since the start of mass production in the 1950´s and the negative impacts of marine plastic debris (MPD) on marine life are general acknowledged. Typically, MPD is overgrown by diverse biofilms comprised of prokaryote and eukaryotes, but it is mostly unresolved whether polymers are colonized by opportunist that attach to any hard surface, or if different polymers attract specific communities. This question is further complicated by the fact that floating MPD is subjected to UV-induced photo-oxidation, which results in polymer degradation, i.e. the release of smaller and more bioavailable daughter products, and also causes changes in the polymer’s surface properties. If weathered surfaces are more prone to colonization than pristine ones and whether communities on these surfaces are different is unknown. In consonance, whether colonizers interact with the different polymers, e.g. degrade it, or are just ‘hitching a ride’ is ambiguous. To solve this complex problem we investigated the initial colonization of pristine plastics and the influence of photo-oxidation on community succession. We incubated five different polymer types (PE, PP, PET, PS and Nylon; one set UV pre-treated, one set pristine), in shallow coastal waters of the Caribbean island St. Eustatius at a depth of 5m. Multivariant-analyses to compare day 1 and day 6 revealed that the microbial community changed over time, which is a typical feature during colonisation. Communities of day 1 and day 6 were also analysed separately to assess the influences of UV pre-treatment and polymer type during separate stages of biofilm development. On day 1, UV pre-treated foils attracted a different community than non-pre-treated foils, while there was no statistical difference in community composition between the five polymer types. In contrast, on day 6, the influence of UV treatment on community composition was no longer significant, while different polymer types supported different communities. These results show that the community is dynamic in the initial stage of colonization of polymers. The effects of UV pre-treatment and polymer type indicate that colonizers are not purely opportunistic. With more in-depth analysis on OTU and/or order level, we aim to answer the following questions: 1) What is the main driver for community succession 2) Are there polymer-specific members of the community 3) Do the different polymer types select for communities that might utilise the polymer or its UV-degradation products for energy gain and/or growth.