Study area: The main field study was conducted in a coral reef offshore from the Richard Gump South Pacific Research Station located next to Cook's Bay on the northern shore of Mo'orea, French Polynesia. Research was conducted by small boat in a shallow-water coral reef and offshore Pacific Ocean. See Figure 1 in Xue et al. 2022 (under review) for the geographic locations of French Polynesia, the island of Mo'orea, and the schematic description of the reef structure and the reef-ocean transect sampling locations.

Sample collection and storage: Water samples were collected from the near sea surface using precleaned polypropylene bottles from repeated sampling trips to six hydrographic stations along a reef-ocean transect. To collect samples for dissolved concentrations, the unfiltered samples were gravity filtered through a precombusted GF/F filter into precleaned 20 milliliter (mL) scintillation vials following the procedure of small-volume drip filtration (Kiene and Slezak 2006). Paired with each dissolved sample, another set of samples was also collected for the measurement of total concentrations by transferring 15 mL of unfiltered seawater into 20 milliliter (mL) scintillation vials. All samples were microwaved to boiling and allowed to cool to room temperature followed by bubbling using high-purity nitrogen and acidification with 150 microliters of Ultrex-grade HCl. Each sample was collected in duplicate and was stored at room temperature in the dark until analyses were conducted in the home laboratory in Syracuse, New York.

Acrylate and organosulfur quantification: Acrylate concentrations were determined using a pre-column derivatization HPLC method (Xue and Kieber 2021). For derivatization, 300 microliter (µL) thiosalicylic acid (20 mM) reagent was added into a 5 mL precleaned borosilicate vial containing 3 mL of a standard or seawater sample. The pH in each vial was adjusted to 4.0. Then each vial was tightly screw-capped and incubated at 90 degrees Celsius in a water bath for 6 hours. After cooling to room temperature, each derivatized sample was filtered using a 0.2 µm Nylon syringe filter followed by injection of 1 mL sample into a Shimadzu reverse-phase HPLC with UV absorbance detection at 257 nanometers (nm). To measure concentrations of DMSP and DMSO, both compounds were first converted to DMS. To convert DMSP or DMSO to DMS, 200 µL 5 M NaOH or 20% TiCl3 was added to 1 mL of a standard or seawater sample in a precleaned borosilicate serum vial, which was immediately capped and sealed followed by incubation. Incubation for DMSP was overnight at room temperature, while incubation for DMSO was at 55 degrees C for 1 hour. The produced DMS was analyzed using a cryogenic purge-and-trap system and a Shimadzu GC-14A with a flame photometric detector (Kinsey et al., 2016).

Chlorophyll a (Chl a): 250 ml of seawater was filtered through a 25 millimeter (mm) diameter GF/C glass fiber filter that was subsequently stored frozen. The fluorescence of the extracts was measured with a calibrated Turner designs fluorometer

Notes: Concentrations (column C-H) in dissolved or unfiltered (total) samples are given in units of nanomole/L with subscripts d and t indicating dissolved and total concentrations, respectively.