A High-Resolution Time Series Reveals Distinct Seasonal Patterns of Planktonic Fungi at a Temperate Coastal Ocean Site (Beaufort, North Carolina, USA)

Abstract

There is a growing awareness of the ecological and biogeochemical importance of fungi in coastal marine systems. While highly diverse fungi have been discovered in these marine systems, still, little is known about their seasonality and associated drivers in coastal waters. Here, we examined fungal communities over 3 years of weekly sampling at a dynamic, temperate coastal site (Pivers Island Coastal Observatory [PICO], Beaufort, NC, USA). Fungal 18S rRNA gene abundance, operational taxonomic unit (OTU) richness, and Shannon's diversity index values exhibited prominent seasonality. Fungal 18S rRNA gene copies peaked in abundance during the summer and fall, with positive correlations with chlorophyll , SiO, and oxygen saturation. Diversity (measured using internal transcribed spacer [ITS] libraries) was highest during winter and lowest during summer; it was linked to temperature, pH, chlorophyll , insolation, salinity, and dissolved inorganic carbon (DIC). Fungal communities derived from ITS libraries were dominated throughout the year by, with contributions from ,, and , and their seasonal patterns linked to water temperature, light, and the carbonate system. Network analysis revealed that while cooccurrence and exclusion existed within fungus networks, exclusion dominated the fungus-and-phytoplankton network, in contrast with reported pathogenic and nutritional interactions between marine phytoplankton and fungi. Compared with the seasonality of bacterial communities in the same samples, the timing, extent, and associated environmental variables for fungi community are unique. These results highlight the fungal seasonal dynamics in coastal water and improve our understanding of the ecology of planktonic fungi. Coastal fungal dynamics were long assumed to be due to terrestrial inputs; here, a high-resolution time series reveals strong, repeating annual patterns linked to environmental conditions, arguing for a resident coastal fungal community shaped by environmental factors. These seasonal patterns do, however, differ from those observed in the bacterioplankton at the same site; e.g., fungal diversity peaks in winter, whereas bacterial diversity maxima occur in the spring and fall. While the dynamics of these communities are linked to water temperature and insolation, fungi are also influenced by the carbonate system (pH and DIC). As both fungi and heterotrophic bacteria are thought to be key organic-material metabolizers, differences in their environmental drivers may offer clues as to which group dominates secondary production at this dynamic site. Overall, this study suggests the unique ecological roles of mycoplankton and their potentially broad niche complementarities to other microbial groups in the coastal ocean.

Microbial communities across nearshore to offshore coastal transects are primarily shaped by distance and temperature

“…4A) includes samples from Stations A to C when the water temperature is <19 C, relative to the warmer offshore temperatures >22 C at Stations D and E in these same transects. This temperature-related seasonal signal aligns with previous studies at Station A, which found that temperature is the strongest environmental factor correlated with microbial community changes (Ward et al, 2017;Duan et al, 2018) as well as other studies that observed secondary seasonal patterns layered on top of strong spatial patterns (Fortunato et al, 2012). Supporting this hypothesis, taxa that increased in these cool winter samples were previously identified as winterassociated in the PICO time series (Ward et al, 2017).…”

“…This study builds on previous research that found strong temperature‐associated annual patterns in microbial communities at the PICO time series (Ward et al ., ; Duan et al ., ). These PICO‐LOVE transects begin at the PICO time series site (Station A) and cross the mid‐Atlantic continental shelf, depth < 160 m (Day et al ., ), for a total distance of 87 km to Station E, at the edge of both the continental shelf break and the warm, oligotrophic waters of the Sargasso Sea.…”

“…In order to better understand the microbial community diversity and dynamics in the coastal oceans, we repeatedly sampled surface water transects from the North Carolina coast to the edge of the Sargasso Sea. Starting at the Piver's Island Coastal Observatory (PICO) a well‐characterized weekly time‐series site at the mouth of an estuary (Johnson et al ., ;Ward et al ., ; Duan et al ., ), we sampled a transect across the continental shelf to the oligotrophic waters of the Sargasso Sea as part of the PICO‐Longitudinal Observational Variability Experiment (PICO‐LOVE) a total of 15 times (Supporting Information Table S1), although not all stations were sampled in each transect. At this site, freshwater inputs are generally low, resulting in minimal salinity differences across the transect and allowing us to focus on investigating microbial community transitions across the other chemical, physical and biological gradients in the coastal ocean.…”

Diverse groups of fungi are associated with plastics in the surface waters of the Western South Atlantic and the Antarctic Peninsula

“…Other marine debris such as wood also harbour fungi, suggesting that Fungi are well adapted to live on different types of floating marine substrates (Kettner, Oberbeckmann, Labrenz, & Grossart, 2019; Kettner et al., 2017). The abundance and diversity of fungi in coastal waters varies seasonally in response to environmental variables such as particulate organic carbon (Duan et al., 2018; Taylor & Cunliffe, 2016), which could also affect how and which fungal taxa colonize plastics.…”

Seasonal Dynamics of Pelagic Mycoplanktonic Communities: Interplay of Taxon Abundance, Temporal Occurrence, and Biotic Interactions

“…Marine microbial plankton, including fungi, are exposed to a highly fluctuating environment, which is reflected in changing diversity and structure (Gilbert et al, 2012;Lucas et al, 2016;Taylor and Cunliffe, 2016;Teeling et al, 2016;Duan et al, 2018). The dynamics within marine microbial communities can be described by different patterns (Needham et al, 2013), ranging from relatively small variations around an average to rapid increases and decreases within a very short time.…”