Abstract
Diatom communities significantly influence ocean primary productivity and carbon cycling, but their spatial and temporal dynamics are highly heterogeneous and are governed by a complex diverse suite of abiotic and biotic factors. We examined the seasonal and biogeographical dynamics of diatom communities in Australian coastal waters using amplicon sequencing data (18S-16S rRNA gene) derived from a network of oceanographic time-series spanning the Australian continent. We demonstrate that diatom community composition in this region displays significant biogeography, with each site harbouring distinct community structures. Temperature and nutrients were identified as the key environmental contributors to differences in diatom communities at all sites, collectively explaining 21% of the variability observed in diatoms assemblages. However, specific groups of bacteria previously implicated in mutualistic ecological interactions with diatoms (Rhodobacteraceae, Flavobacteriaceae and Alteromonadaceae) also explained a further 4% of the spatial dynamics observed in diatom community structure. We also demonstrate that the two most temperate sites (Port Hacking and Maria Island) exhibited strong seasonality in diatom community and that at these sites, winter diatom communities co-occurred with higher proportion of Alteromonadaceae. In addition, we identified significant co-occurrence between specific diatom and bacterial amplicon sequence variants (ASVs), with members of the Roseobacter and Flavobacteria clades strongly correlated with some of the most abundant diatom genera (Skeletonema, Thalassiosira, and Cylindrotheca). We propose that some of these co-occurrences might be indicative of ecologically important interactions between diatoms and bacteria. Our analyses reveal that in addition to physico-chemical conditions (i.e., temperature, nutrients), the relative abundance of specific groups of bacteria appear to play an important role in shaping the spatial and temporal dynamics of marine diatom communities.
Highlights
Diatoms (Bacillariophyta) are one of the most abundant and diverse groups of marine phytoplankton, and are responsible for approximately 20% of global marine primary productivity [1,2]
We identified the diatom amplicon sequence variants (ASVs) that exhibited sudden and repeated increases in relative abundance between years, to identify diatom bloom dynamics at each of the three time-series sites
We identified temperature and nutrients as key environmental determinants explaining most of the spatial variation in diatom assemblages, which was reflected in a transition of community structure from tropical to temperate climates
Summary
Diatoms (Bacillariophyta) are one of the most abundant and diverse groups of marine phytoplankton, and are responsible for approximately 20% of global marine primary productivity [1,2] These unicellular photosynthetic eukaryotes constitute the base of the marine food web [3,4], and are especially abundant in coastal regions and polar nutrientrich waters [5,6,7]. Microorganisms 2022, 10, 338 frustules rapidly sink to the ocean’s seafloor and contribute to carbon sequestration [8] Given their ecological and biogeochemical importance, identifying the factors that influence diatom assemblage structure and diversity over space and time is essential for understanding the processes governing marine ecosystem productivity and function. This can lead to bloom events that last for days to weeks and sometimes induce a succession of small faster-growing species (e.g., Thalassiosira, Skeletonema, Pseudo-Nitzschia) initially dominating the consortia, followed by larger diatoms (e.g., Rhizosolenia, Leptocylindrus) [12,13]
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