Supporting Information Data for Bittner et al. 2026 including environmental data of Neuse River Estuary, North Carolina (USA), and dissolved and particulate B-vitamin measurements.

LOD and LOQ are given in fmol. Response of OH-pseudocobalamin and Me-pseudocobalamin assumed to be the same as for OH-cobalamin and Me-cobalamin, respectively. Asterisk (*) indicates values between LOD and LOQ were verified by the batch per batch method, otherwise only values above LOQ were quantified.</p><p dir="ltr"><b>Data S3</b>.

Concentrations of B-vitamins and vitamers present in the dissolved (<b>A</b>), small particulate (0.2-3 µm) size-fraction (<b>B</b>), and large (3-90 µm) particulate size-fraction (<b>C</b>) in the near-surface waters of the Neuse River Estuary across time points and stations sampled. Number of biological replicates for each sample for which data is available is provided in the column labelled n, as some replicates were lost during sample processing or measurement (see Methods).

Not all metabolites were detected in all biological replicates as, therefore the number of biological replicates, on which the measurement is based, is provided for each metabolite. If the metabolite was detected in minimum three replicates the standard deviation (sd) is listed. LOD: measurements were below limit of detection.

LOQ: measurements were below limit of quantification. Compounds specific LODs and LOQs are provided per dataset and matrix grouping in Supporting Information <b>Data S2</b>.</p><h3 dir="ltr"><b>ABSTRACT</b></h3><p dir="ltr">B-vitamins are organic cofactors required by prokaryotic and eukaryotic planktonic cells; their availability impacts aquatic microbial communities and associated biogeochemistry. Despite their ecological importance, B-vitamin dynamics and their relationships to plankton composition in estuaries are unclear, limiting our under- standing of estuary biology in general as well as how B-vitamins are distributed in marine systems.

Here, we simultaneously quantified multiple B-vitamins and their vitamers (vitamin related compounds, e.g., precursors for de novo synthesis) in particulate and dissolved phases. Alongside, we characterized the prokaryotic and eukaryotic microbial communities across freshwater to polyhaline zones of the Neuse River Estuary (NRE), North Carolina, USA from summer to fall. We found notable autochthonous B-vitamin production in the estuary, and the mid- estuary emerged as a zone of increased levels of B-vitamins fueled by algal growth.

B-vitamin and vitamer concen- trations were highly dynamic on short time scales (weeks) and we identified two specific dynamic modes. Moderate concentration changes likely driven by production/consumption and sporadic rapid concentration peaks presum- ably driven by shifts in plankton community composition. We identified vitamin B1,B12,psB12 (pseudo- cobalamin), and B3 as key explanatory variables for change in prokaryotic and eukaryotic NRE plankton, revealing B-vitamins as important compounds for resolving variability of plankton communities in estuaries.

Our study pro- vides insights into the dynamic concentrations of B-vitamins and vitamers across zones of estuaries and provides new evidence of B-vitamin influence upon plankton community composition.<br></p><p dir="ltr">DOI: <a href="doi.org/10.1002/lno.70508" target="_blank" rel="noreferrer">10.1002/lno.70508</a><br></p>