The experiments were conducted at the Research Field Station Marine Lab (FSML) Kaneohe Bay, Hawaii, (HIMB; 21.4326 ˚, -157.7866˚).

The following sections contain methodology excerpts from Quinlain et al. (2018) relevant to this dataset.

Collection of major reef constituents:

Three visibly healthy colonies each of Porites compressa and Montipora capitata, two locally abundant hermatypic corals, were collected between 4 and 7 meters depth from fringing reef immediately adjacent to the Hawai'i Institute of Marine Biology in Kāne'ohe Bay, Hawai'i (HIMB; 21.435 ˚, -157.787˚) between 12 and 16 October 2015. Each colony was fragmented into 36 nubbins and one nubbin from each colony was mounted onto each of 36 polystyrene frames (roughly 10 cm2) using epoxy putty. Each frame had 6 nubbins (3 Porites, 3 Montipora); one nubbin from each colony per frame; 24.8 ± 5.23 g dry weight P. compressa, 21.9 ± 5.05 g dry weight of M. capitata. Corals were allowed to acclimate 10 days before the start of the experiment. Rubble of dead skeleton from P. compressa skeleton was haphazardly collected in conjunction with the coral collections, separated into 36 equal portions (78.9 ± 3.42 g dry weight) and contained within polyethylene mesh netting containers. The macroalga Gracilaria sp. (Rhodophyta) was collected from the north point of HIMB (21.4360˚, -157.7881˚); any visible invertebrates and epiphytes within the macroalgae were removed, fronds were separated into 36 equal portions (11.0 ± 0.55 g wet weight) and contained within polyethylene mesh netting mesh containers. Sand was collected from the top 3 cm of aerobic reef sand on the eastern edge of HIMB (21.4350˚, -157.7871˚) using a 7.5 cm diameter core and was left undisturbed in each of the 36 petri dishes in which it was collected.

Aquaria and nutrient enrichment systems:

Square polycarbonate aquaria (n = 36) were affixed with an upper spigot drain to hold water level constant at 6 L, acid washed and soaked for 72 hours in flowing seawater to leach plasticizers prior to the experiment, scrubbed clean, rinsed with freshwater and dried. Each aquarium was filled with 4 benthic constituent units (either four coral frames, four algal or rubble mesh portion containers or four sand dishes) and placed into one of three 1300L flow-through seawater tanks (12 aquaria per tank) as water baths to maintain stable temperature. Each tank thus contained one replicate aquarium of each benthic group maintained at each nutrient level (Figure 1, Quinlain et al. 2018). Source water from Kāne'ohe Bay was filtered through a sand filter followed by a 20 µm polyethylene cartridge pre-filter to exclude large plankton. A concentrated nutrient mix (2 mmol L-1 sodium nitrate and 0.67 mmol L-1 monosodium phosphate, 20L) was prepared every other day by amending seawater with a frozen concentrated stock in a pre-cleaned polycarbonate carboy stored at ambient temperatures in the dark. Both the source water and nutrient mixture were pumped by continuous peristalsis through platinum cured silicone tubes into nutrient mixing aquaria with 90 minute residence times maintained at three concentrations (ambient, low and high; mean and time series concentrations in Figure 1 and Figure S2, respectively, Quinlain et al., 2018) then distributed by peristalsis to the experimental aquaria maintained at a 5-hour residence time. Each week all aquaria were replaced with cleaned and dried aquaria and randomly rearranged spatially within incubation tanks, but maintained in three replicate experimental blocks cycled among 1300 L tanks to account for light and temperature variation; means of 288 ± 354 µmol photon m-2 s-1 and 25.9 ±1.9 ˚C did not differ significantly among water baths and are detailed in a companion manuscript (Silbiger et al., 2018).

Dissolved Organic Matter (DOM) sample collection and analysis:

DOM samples were collected biweekly over a period of four weeks from each aquaria using acid washed and seawater leached treatment-specific, rubber free polyethylene syringes and filtered through a 0.2 µm polyethersulfone filter (25 mm; Sterlitech) in a polypropylene filter holder (Swin-lok; Whatman). Filtrate was collected in acid washed, combusted, triple sample-rinsed amber borosilicate vials with teflon septa lids and stored dark at 4˚C until analysis within 1 month of collection. Dissolved organic carbon (DOC) was measured as non-purgeable organic carbon via acidification, sparging and high temperature platinum catalytic oxidation on a Shimadzu TOC-V (Carlson et al. 2010). Nutrient samples were collected identically, but frozen (-20 °C) in polyethylene centrifuge tubes, thawed to room temperature, mixed thoroughly and analyzed on a Seal Analytical Segmented Flow Injection AutoAnalyzer AA3HR for simultaneous determination of soluble reactive phosphate (PO43-), ammonium (NH4+), nitrate + nitrite (N + N; NO3- + NO2-), silicate (SiO4) and total dissolved nitrogen and phosphorus (TDN, TDP; via in-line persulfate/ultraviolet oxidation). Dissolved organic nitrogen (DON) was calculated as the difference between TDN and the sum of ammonium, nitrate and nitrite.

Samples for fluorescence spectroscopy were measured using an Horiba Aqualog scanning fluorometer following the methods of Nelson et al. (2015) and processed using a Matlab (v2007b) script (see processing section below). Six PARAFAC components were validated using split half validation and outlier analysis (Figure S1, Quinlain et al., 2018). All PARAFAC components had similar excitation-emission maxima and strong covariation among samples with previously identified fluorophores; thus for subsequent analyses, we examined established fluorescence maxima from the literature (Table S1, Quinlain et al., 2018; Coble ,1996; Stedmon et al., 2003; Lakowicz, 2010).