Long-term seasonal patterns of free-living and particle-attached marine bacteria in a temperate coastal ecosystem

2018 Ocean Sciences Meeting, 11-16 February, in Portland, OregonHigh-throughput sequencing techniques (HTS) provide detailed descriptions of natural microbial assemblages and their dynamics. Temporal sampling coupled with these techniques has shown that, in temperate marine ecosystems, free-living (FL) bacterioplankton shows stable annual patterns. Likewise, the FL and particle-attached (PA) microbial communities have been shown to differ in composition with many bacteria exhibiting preferences for either a PA or FL lifestyle. Here, we investigated the long-term (10 years) dynamics and predictability of FL and PA bacterial assemblies in the Blanes Bay Microbial Observatory (NW Mediterranean). We found that both size-fractions show clear seasonal patterns of alphadiversity with higher richness in fall and winter. Community structure clearly differed both by season and size-fraction, being the former a stronger driver than the latter. We observed that both seasonality and lifestyle trends vary depending on taxonomy. Groups such as Planctomycetes or Verrucomicrobia showed PA preference whereas the SAR11 clade and the Rickettsiales are clear examples of FL bacteria. Along, several taxa showed synchronic patterns of abundance with a 1-year periodicity. At the OTU (Operational Taxonomic Unit) level, only 26% showed recurrent seasonality but these represented the most abundant ones (92% of total reads). When teasing apart the FL and PA fractions, we found a higher proportion of seasonal OTUs in the FL than in the PA fraction. Yet, time-decay curves confirmed that there is a high degree of predictability in both size fractions. Moreover, the analysis of the temporal series revealed that, for about two years, the PA community intriguingly differed from the predictable one. Interestingly, this period coincides with the construction of a nearby harbor. Our results show that the synchrony of bacterioplankton can be overwhelmed by perturbations such as harbor engineering, but communities are able to recover once the perturbation ceasesPeer Reviewe