Unscrambling Cyanobacteria Community Dynamics Related to Environmental Factors

Abstract

Future climate scenarios in the Baltic Sea project an increase of cyanobacterial bloom frequency and duration, attributed to eutrophication and climate change. Some cyanobacteria can be toxic and their impact on ecosystem services is relevant for a sustainable sea. Yet, there is limited understanding of the mechanisms regulating cyanobacterial diversity and biogeography. Here we unravel successional patterns and changes in cyanobacterial community structure using a 2-year monthly time- series during the productive season in a 100 km coastal-offshore transect using microscopy and high-throughput sequencing of 16S rRNA gene fragments. A total of 565 cyanobacterial OTUs were found, of which 231 where filamentous/colonial and 334 picocyanobacterial. Spatial differences in community structure between coastal and offshore waters were minor. An “epidemic population structure” (dominance of asingle cluster) was found for Aphanizomenon/Dolichospermum within the filamentous/colonial cyanobacterial community. In summer, this clusters imultaneously occurred with opportunistic clusters/OTUs, e.g., Nodularia spumigena and Pseudanabaena. Picocyanobacteria, Synechococcus/Cyanobium, formeda consistent but highly diverse group. Overall, the potential drivers structuring summer cyanobacterial communities were temperature and salinity. However, the different responses to environmental factors among and within genera suggest high niche specificity for individual OTUs. The recruitment and occurrence of potentially toxic filamentous/colonial clusters was likely related to disturbance such as mixing events and short-term shifts in salinity, and not solely dependent on increasing temperature and nitrogen-limiting conditions. Nutrients did not explain further the changes in cyanobacterial community composition. Novel occurrence patterns were identified as a strong seasonal succession revealing a tight coupling between the emergence of opportunistic picocynobacteria and the bloom offilamentous/colonialclusters. These findings highlight that if environmental conditions can partially explain the presence of opportunistic picocyanobacteria, microbial and trophic interactions with filamentous/colonial cyanobacteria should also be considered as potential shaping factors for single-celled communities. Regional climate change scenarios in the Baltic Sea predict environmental shifts leading to higher temperature and lower salinity; conditions identified here as favorable for opportunistic filamentous/colonial cyanobacteria. Altogether, the diversity and complexity of cyanobacterial communities reported here is far greater than previously known, emphasizing the importance of microbial interactions between filamentous and picocyanobacteria in the context of environmental disturbances.

Local Environmental Conditions Shape Generalist But Not Specialist Components of Microbial Metacommunities in the Baltic Sea

“…We used samples collected from monthly transects during April to October 2011 along a 100-km transect off the east coast of Sweden in the western Gotland Sea of the Baltic Sea Proper (for a detailed description of the study area and environmental conditions, see Diaz-Gil et al, 2014; Legrand et al, 2015; Bertos-Fortis et al, 2016). In brief, unfiltered natural seawater was collected in acid washed Milli-Q rinsed polycarbonate bottles, at discrete depths (2, 4, 6, 8, and 10 m) that were pooled and filtered shipboard on to 47 mm 0.2 μm Supor filters (Pall corporation).…”

“…Our aim was to examine assembly processes for structuring bacterioplankton community composition and biogeography using samples collected from monthly transects during April to October 2011 along a 100-km transect off the east coast of Sweden in the western Gotland Sea of the Baltic Sea Proper (Diaz-Gil et al, 2014; Legrand et al, 2015; Bertos-Fortis et al, 2016). Using 16S rRNA gene fragments we investigated (i) phylogenetic relatedness over time, (ii) differences in community assembly mechanisms over time, and between taxa, and (iii) how niche breadth influenced community assembly.…”

Influence of Major Storm Events on the Quantity and Composition of Particulate Organic Matter and the Phytoplankton Community in a Subtropical Estuary, Texas

“…Given the importance of cultivated crops in the Mission-Aransas watershed, understanding the impact of freshwater inflows on the phytoplankton community in this estuary is key to the management of these vital sporadic freshwater inflows. Furthermore, cyanobacteria show extreme plasticity toward changes in environmental conditions and aquatic systems across the world, and cyanobacterial bloom frequency and duration are projected to increase in response to climate change (Paerl et al, 2014a;Bertos-Fortis et al, 2016).…”

“…dominated during the low salinity summer 2015 wet period, and Prochlorococcus spp. dominating during the high salinity summers of 2013 and 2014 (Figures 2B, 4A; Supplementary Figure 3A; Bertos-Fortis et al, 2016).…”

“…occurrence was associated with lower salinities (Cai et al, 2010). In a study of cyanobacterial communities in the upper mixed layer (0-10 m) of the Baltic Sea, temperature and salinity were the potential drivers in structuring summer cyanobacterial communities (Bertos-Fortis et al, 2016). Picocyanobacteria were present in this layer year-round, and Cyanobium spp., in particular, have the ability to thrive in dynamic environments (such as the MAE) which is the reason for their year-round presence despite seasonal changes (BertosFortis et al, 2016).…”