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) 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.

Water samples: A study was conducted to determine the rate constant and rate for the biological consumption of dissolved acrylate and DMSP. Experiments were performed using unfiltered water samples collected during diel sampling in the back reef and open Pacific Ocean stations.

Biological consumption of dissolved acrylate: To perform an incubation experiment for the biological consumption of acrylate, acrylate was added to unfiltered water samples in triplicate 250 milliliter (mL) polycarbonate (PC) bottles to yield an initial concentration of 10-15 nanomolar (nM). Another set of three PC bottles received no acrylate addition. Once samples were prepared, they were placed in a large incubator with hosing to continuously pump ambient seawater through the incubator to maintain the temperature at ~28 degrees Celsius. Samples were incubated in the dark. Subsamples (15 mL) were collected at four time points from each PC bottle during incubation, and the total length of each incubation was 14 hours for the back reef samples and 18 hours for the Pacific Ocean samples.

Biological consumption of dissolved DMSP: The biological consumption of DMSP was determined using the glycine betaine (GBT) inhibition method outlined in Kiene and Gerard (1995). Briefly, six PC bottles were filled with freshly collected, unfiltered seawater. Three bottles were treated with GBT to a final concentration of 10 micromolar (µM) and the other three bottles were left untreated. All samples were incubated in dark in the same incubator used for acrylate experiments. Subsamples (15 mL) were collected at several time points from each bottle for the measurement of DMSP concentrations.

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 milliliter (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 micrometer (µm) Nylon syringe filter followed by injection of a 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 overnight for DMSP at room temperature or for DMSO 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).

Notes: All samples from the biological consumption experiments were processed, stored, and analyzed for acrylate and DMSP using the same procedures used to measure DMSP and acrylate concentrations in the transect study (https://www.bco-dmo.org/dataset/879142).

Kbio_acrylate and Kbio_DMSP denote the first-order rate constants for biological consumption of acrylate and DMSP in the unit of per day (d-1).

Dissolved acrylate (Acrylate_d) and dissolved dimethylsulfoniopropionate (DMSP_d) concentrations were determined in the water samples used for the biological consumption experiments.

The concentrations of acrylate or DMSP at different time points were fit into a first-order decay kinetic model and the rate constants (+/- standard deviation) were determined by taking the slope of the best-fit line from linear regression analysis.

The biological consumption rate was calculated by multiplying the concentration of acrylate or DMSP with the rate constant in each sample.

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