Search

Highlights • Study of the ecosystem's response to ITW events in the Adriatic • Introduction of the adaptive sampling design based on metocean numerical forecasts • Bacterioplankton composition and net primary production responded to ITWs • ITWs did not influence eukaryotic community diversity or abundances Abstract The oligotrophic Adriatic Sea is characterized during a typical summer by low productivity caused by strong water column stratification, which inhibits vertical mixing and nutrient supply to the euphotic zone. These conditions can be disrupted by transient physical forcing, which enhances nutrient fluxes and creates localized hotspots of relatively high net primary production. In this study, plankton abundance and diversity were investigated in relation to the physical forcing and nutrient concentrations in an area affected by island-trapped waves (ITWs) near Lastovo Island (Adriatic Sea). The episodic ITW events resulted in enhanced uplift and vertical excursion of the thermocline, marked by anomalously higher nutrient concentrations and a corresponding increase in net primary production in the thermocline layer. Physicochemical properties explained 11.7% (p = 0.002) of the variability in micro- and nanophytoplankton and 88.9% (p = 0.001) in the picoplankton community. A significant response to the ITW phenomenon in the plankton community composition (p = 0.001) was observed for bacterioplankton. Among the identified amplicon sequence variances, primary producers were scarce and mainly represented cyanobacteria (Synechococcus strain CC9902), stramenopiles (Pelagomonas), and chlorophytes (Ostreococcus). The remaining amplicon sequence variances were assigned to the classes Copepoda, parasitic fungi (Meyerozyma spp.), mixotrophic dinoflagellates (family Peridiniales, mostly the genus Blastodinium), and parasitic Ciliophora (Scuticociliata). Bacterial ecological functions corresponded to chemoheterotrophic, degradation, and fermentation processes, whereas s

The Northern Adriatic Sea is a key area of the Mediterranean Sea, strongly affected by freshwater inputs, mainly from the Po River, which bring high amounts of nutrients as well as organic and inorganic particles. Free-living and particle-attached prokaryotes were characterized by 16S rRNA gene amplicon sequencing of size-fractionated samples collected during a diatom bloom in this area. The diversity of free-living and particle-attached prokaryotic assemblages was investigated with the aim to understand how the microbial communities are structured in the two fractions and whether specific microbial groups are associated to one lifestyle or the other. The results highlight a diverse prokaryotic community dominated by Proteobacteria, Bacteroidetes, and, remarkably, Firmicutes. Taxa within Firmicutes and Alphaproteobacteria are identified as the main particle-attached indicators by LEfSe, while members of Bacteroidetes and Gammaproteobacteria were representative of the free-living lifestyle, although they were also usually found as particle-attached. Collectively, the results suggest that both the free-living and the particle-attached lifestyles are a complex combination of specialization and adaptation to local conditions

Polyunsaturated aldehydes (PUAs), produced as secondary metabolites by diatoms, have been shown to induce toxic effects on a variety of organisms, including copepods and phyto- and bacterioplankton. However, the nature of and the players in this interaction remain poorly understood. We tested the effect of 3 PUAs commonly produced by marine diatoms—2E,4E/Z-heptadienal (HEPTA), 2E,4E/Z-octadienal (OCTA), 2E,4E/Z-decadienal (DECA) and a mix of HEPTA and OCTA (MIX)—on a natural bacterial community from a coastal area of the NW Mediterranean Sea (Blanes Bay, Spain). Little effect on total or relative cell abundance or bulk bacterial production was observed after 6 or 24 h exposure to 7.5 nM of the 3 different PUAs for the different bacterial phylogenetic groups (Gammaproteobacteria, Bacteroidetes, Rhodobacteraceae and SAR11), assessed by catalysed reporter deposition (CARD)-fluorescence in situ hybridisation (FISH). Metabolic activity, i.e. single-cell activity as determined by microautoradiography combined with CARD-FISH (MAR-CARD-FISH), was least affected by the addition of single PUAs in Gammaproteobacteria, markedly in Bacteroidetes and most markedly in Rhodobacteraceae, leading to a decrease in Rhodobacteraceae abundance by 21% (by 38% of the active cells assessed by leucine uptake) compared to the control. Bacteroidetes, although markedly affected in single-cell activity, were the most abundant group (54% of total cell counts). The addition of a mixture of OCTA and HEPTA produced a more pronounced decrease in the metabolic activity of all groups than the incubation with the single PUAs, suggesting a synergistic effect. Our results demonstrate that PUAs have a differential effect on the single-cell activity of distinct bacterial groups in natural communities. PUAs may therefore play an important role in shaping bacterial community composition by conferring a competitive advantage to PUA-resistant groups, allowing them to preferentially use the organic matter releas