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Saltmarshes, seagrass meadows and mudflats are key habitats in estuarine ecosystems. Despite being involved in key ecological processes, the influence of different estuarine habitats on sediment bacterial communities remains understudied. Few studies have analysed and compared the bacterial communities of more than one estuarine habitat at different depths. Here, we investigated to what extent different habitats (mudflats; mono-specific plots of seagrass [ Zostera noltei] and two saltmarsh plants [ Juncus maritimus and Spartina maritima]) and sampling depth (0, 5, 10 cm) influence variation in sediment bacterial composition. Our results showed significant differences in the abundance of selected higher taxa amongst habitats and depths. Surface sediment was characterized by bacteria assigned to the Acidimicrobiia, Flavobacteriia, Thiotrichales, Alteromonadales and Rhodobacterales, whereas in deeper sediment Deltaproteobacteria and Anaerolineae were dominant. Juncus sediment, in turn, presented the most distinct bacterial community, with Myxococcales abundant in this habitat. Sampling depth and habitat proved significant predictors of variation in sediment bacterial composition. The compositional dissimilarities amongst habitats and depths suggest functional divergence and complementarity, thus enhancing ecosystem functioning and health. Given the compositionally distinct communities found in different habitats and depths, our study corroborates the importance of conserving a diverse array of estuarine habitats. [ABSTRACT FROM AUTHOR]

The uppermost millimeter of the water column, the surface microlayer (SML), hosts bacterial communities (bacterioneuston) with potential metabolic adaptations to this unique physical and chemical environment. Hydrolysis and monomer incorporation by bacterioneuston and bacterioplankton communities in the estuarine system, Ria de Aveiro, was investigated and compared during a 2-year survey. The study was conducted at two contrasting sites, typifying the marine and brackish water characteristics of the estuary and with different sources, amounts and composition of organic matter. In the marine zone, bacterioneuston showed higher rates of hydrolysis and lower rates of monomer incorporation than bacterioplankton, whereas in the brackish water zone, neustonic and planktonic microbial communities showed similar activity rates. This pattern may result from the different degree of surface organic and inorganic matter enrichments, which reflect site-specific characteristics, such as hydrodynamics and sources of organic matter composition. In general, the estuarine SML environment favors polymer hydrolysis, but inhibits monomer utilization, in comparison with the subsurface layers. However, the differences between the two communities tend to decrease as autotrophic and heterotrophic activities increase in the brackish-water area. [ABSTRACT FROM PUBLISHER]

Abstract: The influence of freshwater flow on bacterial communities in the estuarine system Ria de Aveiro (Portugal) was investigated at two sites differently impacted by river inputs, representative of the marine and brackish water zones of the estuary. Sampling events were clustered based on hydrological features. The hydrodynamic was simulated with a Lagrangian model and related to microbiological parameters. Estuarine bacteria responded to different freshwater regimes developing distinct patterns of abundance and activity at the marine and brackish water zones. A circulation pattern induced by high river inflow produced vertical stratification in the marine zone, promoting a seaward flux of bacterioplankton, and stimulating the import of riverine phytoplankton and particle-attached bacteria to the brackish water zone. Advective transport and resuspension processes contributed to a 3-times increase in abundance of particle-attached bacteria during intense freshwater inputs. Additionally, bacterial activity in the estuary was controlled by inorganic nitrogen, responding to different freshwater inputs, which, in association with different prevailing sources of organic substrates induced significant changes in bacterial production. The dynamic and main controlling factors of bacterial communities are clearly impacted by freshwater inputs. Therefore, significant changes in the recycling of nutrients by microbial activities can be expected from alterations in freshwater inputs either related to global climate change or regional hydrological regimes. [Copyright &y& Elsevier]