Dataset: Results of a study examining how foundation species loss alters fDOM and heterotrophic bacteria counts based on sampling of tidepools in the Otter Rock Marine Reserve (ORMR) and Marine Garden, Oregon USA from June to August 2019

 fDOM samples were stored in amber glass vials at 4 °C until further processing. Heterotrophic bacterial counts were taken from 1.5 mL unfiltered seawater and stored in 0.5% paraformaldehyde (amended with 100 μL 8% ampulated paraformaldehyde, Electron MicroscopySciences, Hatfield, PA, USA) in a 2 mL polypropylene cryovial, mixed briefly and then frozen to -20 °C. All storage vials were triple rinsed with sample water prior to sample storage. fDOM samples were processed on a Horiba Aqualog scanning fluorometer with 1 cm quartz cuvettes at the University of Hawai’i at Mānoa following Nelson et al. (2015).

All samples were brought to room temperature prior to analysis. Prior to running samples, cuvettes were washed thoroughly with DI water and wiped clear with Kim wipes. Cuvettes were triple rinsed with DI between each sample. A DI blank was run after every 7 samples. Excitation-Emission Matrices (EEMS) were generated with excitation values ranging from 240 nm to 500 nm and emission values were measured ranging from 250 nm to 825 nm.

Excitation wavelengths were increased at 5 nm increments and measurements were integrated over 4 s at each increment. Inner filter correction was applied to account for fluorescence quenching by absorbance (Kothawala et al. 2013). Fluorescence values were scaled to Raman Units by dividing by the integrated emission range of 381 nm to 426 nm at an excitation of 350 nm in averaged DI blanks. The average blank EEMs, from DI blanks run immediately before and after each set of samples, were subtracted from the sample EEMs.

Two biogeochemical informative indices were calculated for this study which included M:C (the relative amount of marine to terrestrial humics) (Burdige et al. 2004) and BIX (biological index) (Huguet et al. 2009). Heterotrophic bacterial counts were analyzed using flow cytometry on an Attune Acoustic Focusing Cytometer with Autosampler Attachment (Life Technologies, Eugene, OR, USA) with methods following Nelson et al. (2015).

Flow cytometry samples were analyzed on fixed 1ml samples run on a Cytoflex Flow Cytometer stained with 7 μL of 40 μL mL−1 Hoechst 34580 (1 μg mL−1 , final concentration) following standard protocols (Nelson et al. 2015; Selph 2021).

Stained cells were distinguished from instrument noise using stained and unstained blank water, and autofluorescent cells containing phytopigments were subtracted from the total to derive the subset of heterotrophic bacterioplankton.