Coral cores (n57) were collected in July 2013 from the shallow reef at Kahekili in Kaanapali, West Maui, Hawaii, from scleractinian Porites lobata (Figure 1) in water depths of between 1 and 3 m and in the vicinity of brackish SGD "seeps" near Kahekili Beach Park (Glenn et al., 2013), approximately 0.5 km southwest of the LWRF (Table 1). All cores were collected from living Porites spp., except for adjacent to the seep where the coral colony was dead upon collection. Colonies were selected based on several criteria including distance from shore, distance from seep, coral shape, and water depth. Metrics of coral reef health (bioerosion,calcification, and growth rate) were quantified at the Woods Hole Oceanographic Institution’s CT Scanning Facility (Crook et al., 2013) where CT scan images (supporting information Figure S1) were used to calculate the proportion of the skeleton eroded (>1 mm boring diameter) by boring organisms and calculated as the total volume of CaCO3 removed relative to the total volume of the individual Porites coral core (Barkley et al., 2015; DeCarlo et al., 2015) using coral CT (DeCarlo & Cohen, 2016). The average growth rate reported in this study is the average linear extension rate and respective standard deviation for the length of cores analyzed per site. Pearson correlation coefficients and respective p values were calculated in Excel. Significance levels were tested at the 95% and 90% confidence level. The number of years for analysis ranged from the upper 10–26 years and was calculated as linear extension (mm) per year. The range (i.e., length of core analyzed) reflects the fact that the quality/preservation of banding was not consistent across the collection sites due to differences in boring and erosion (supporting information Figure S1). In comparison to measured bioerosion rates, predicted bioerosion rates were calculated using the equation from DeCarlo et al. (2015) where bioerosion rate5211.96 * Xarag143.52. Coral life spans were calculated based on annual growth rate and core length. Coral life span for the dead specimen was determined by comparing bomb-derived radiocarbon (14C) values measured at five depth intervals to reference bomb-curves from Hawaii (Andrews et al., 2016). Samples were prepared for Accelerator Mass Spectrometry (AMS) radiocarbon(14C) dating at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility.

Coral nitrogen isotope (d15N) values were determined by collecting skeletal material (300 mg) from the upper 4.0–5.6 mm of growth. Approximately 18 mg of material was placed into tin capsules with an approximately equivalent mass of vanadium oxide (V2O5) catalyst to ensure complete combustion for analysis using a Costech elemental analyzer—Isotope Ratio Mass Spectrometry (EA-IRMS) at the University of California at Santa Cruz and the USGS Stable Isotope Lab to determine d15N composition. Analytical uncertainty of0.16&is reported based on replicate analysis of the international nitrogen standard, acetanilide.

Sampling for water at the primary seep site and in adjacent coastal waters was conducted in September 2014 and March 2016. In 2014, sampling of the submarine springs was conducted using a piezometer point directly inserted into the primary seep site (Swarzenski et al., 2012) and a 12 V peristaltic pump during both high and low tide (supporting information Table S1). At each sampling site, the salinity and temperature of the seep water and bottom water was recorded using calibrated YSI multiprobes. Seawater sampling in March 2016 was conducted near the coral sites every 4 h over a 6 day period for nutrients and carbonate chemistry variables. A peristaltic pump was used to pump seawater from the seafloor and temperature and salinity were recorded using a calibrated YSI multimeter. In situ temperatures were also recorded fromSolonist CTD Divers installed at each sampling tube (Prouty et al., 2017).