Global plastic production has accelerated dramatically over
the past century to over 250 million tonnes produced per year. Most marine
litter originated from land based sources and direct human disposal. Plastics
threaten all trophic levels with injuries caused by ingestion, entanglement and
by toxins or microbial communities on the plastic surface. In particular, micro-organisms
ability to adapt to new niches and provide key ecosystem functions through
primary production and nutrient cycling means their presence on plastics could
have profound influences on both macro and microbiota.
This study investigates the structure and taxonomic
composition of microbial assemblages on plastic fragments in both coastal and
offshore Northern European waters in respect to season, geographical location
and plastic type. To study of assemblages’ spatial and seasonal variation in
the North Sea PET water bottles along with glass slides, for reference, were
attached to smart buoys for six weeks during winter, spring and summer. Two
research cruises used trawled nets at 41 stations during January and July, 2012
to investigate plastic variation of assemblages on plastics already present in
the oceans. Sampling stations encompassed the North Sea, English Channel,
Celtic Sea and Bristol Channel. Samples were imaged using SEM and sequenced
using PCR and Denaturing Gradient Gel Electrophoresis (DGGE), plastic samples
were analysed using Fourier transform infrared spectroscopy (FTIR).
SEM images showed the presence of prokaryotic and eukaryotic
growth on plastic debris, eukaryotes were attached by filamentous stalks. There
was high variability in community structure and composition in relation to
location, season, and polymer type despite some underlying similarities. PET
bottle communities showed greatest difference in winter compared to those in
spring and summer. A high abundance of Bacteriodetes,
Cyanobacteriai, Proteobacteria, and the eukarya Stramenopiles
were identified on all bottles. Bacteriodetes,
including biofilm constituent Tenacbaculum,
were abundant on PET bottles across all seasons and sampling. FTIR analysis did
not reveal any difference in the surface structure of the PET bottles, however
it is unclear whether this is due to lack of microbial action or because this
new technique needs refining. There were clear differences between communities
on the exposed PET bottles and the collected open water fragments. DGGE
analysis on open water fragments showed Cyanobacteria
(predominantly Phormidium and Pseudophormidium) were most dominant
across all plastic types and sampling stations.
Through an investigation of multiple types of plastic in
various locations over a three season time scale this study has highlighted the
variation and hinted at the biodiversity on marine plastics. The majority of
microbiota inhabiting marine plastics are commonly found in natural biofilms
however the study appears to overlook the less abundant bacteria, which could
have novel or harmful effects. Similarities were detected between assemblages
on plastic and glass, implying links between natural and plastic biofilm colonisers. Plastic biofilms pose a higher risk to oceans as it floats
and migrates within water transporting non-native biota.
Obeckmann, S., Loeder, M. G. J., Gerdts, G., Osborn, M. (2014) Spatial and seasonal variation in diversity and structure of
microbial biofilms on marine plastics in Northern European
waters. Microbiology Ecology. 90: 478-492. http://onlinelibrary.wiley.com/doi/10.1111/1574-6941.12409/epdf
Really interesting study, did the paper mention if there were any reasons behind the differences in community structure between winter and spring and summer? Such as certain bacteria present in one season and not in another? And did they use different types of plastic in different sizes/shapes? I'm guessing there are lots of factors that could control the settlement of microbial communities - such as water currents and distance from coast etc. could have an effect. It's interesting that there are similarities between glass and plastic though, which shows some microbes are no affected by the difference in material composition which could be dangerous in the long run as you go up the food chain...
ReplyDeleteThe study suggested environmental parameters were the main mediators of the variation winter and spring and summer as water analysis detected increased temperatures and lower oxygen concentrations in the summer compared to winter. In winter dominant microbes were different at each site, at the most northerly smart buoy the diatom Syndra spp. dominated. Contrastingly, the two other smart buoys were dominated by bacteria: Tenacibaculum (bacteriodetes) and Thiomicrospira (gammaproteobacteria) respectively. In comparison, spring and summer showed higher diversity, summer was dominated by the brown algae Saccharina and Fucus, diatom Asterionella and Cyanobacteria Stanieria and Pseudomrphium across all sites.
DeleteThe work used two experimental techniques: to assess the effects on new plastics they exposed PET bottles, evian water bottles specifically, for 6 weeks of winter, spring and summer then cut them up for sampling. To investigate different types of plastic already in the sea they trawled in sites across the North Sea, English Channel, Celtic Sea and Bristol Channel and collected many different types of plastic in all shapes and sizes.
They also mentioned the need for longer term experiments investigating factors influencing community structure and composition suggesting they were not confident with the effect of environmental factors. You’re right, like so many other in-situ experiments the variability is huge! I think it would be really interesting to run a longer term experiment investigating the assemblages more closely to assess whether the variability is just characteristic of the year of study or of all years.