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Nancy G. Prouty

Publications and source records attributed to Nancy G. Prouty.

At least 19 recordsLinked to original sources
USGS2026

Effect of land-use change and climate on coral calcification and geochemistry: A 253-year time series from west Maui

Land-use change and climate variability both regulate land-based inputs of sediment and nutrient delivery to coral reefs, yet few records in Hawaii can identify when these land-based inputs began or how they have evolved through time. We present a 253-year (1760–2013) coral core record from Olowalu reef, Maui, spanning pre-colonial settlement through the rise and decline of sugarcane agriculture, water diversion, and modern coastal development. Trace element ratios (e.g., Ba/Ca, Y/Ca, P/Ca, Fe/Ca, Sr/Ca) and coral growth parameters document how watershed disturbance and climate variability have influenced reef conditions. Coral trace element records exhibit coherent variability at annual to decadal timescales consistent with El Niño–Southern Oscillation and Pacific Decadal Oscillation frequencies, suggesting climatic control on runoff and groundwater delivery. Superimposed on this natural variability, Ba/Ca, P/Ca, and Fe/Ca increased by 17–55% from the eighteenth century to the late twentieth century, with the largest increase occurring during the mid-1900s and coinciding with the maximum extent of Maui sugarcane plantations. These shifts indicate prolonged increases in sediment and nutrient inputs to the reef. Coral calcification increased by ~30% prior to ~1970 but declined thereafter, coincident with the peak sugarcane production. The negative correlation between coral calcification rate and terrigenous proxies (e.g., Ba/Ca, Y/Ca, P/Ca, and Fe/Ca) suggests that episodic terrestrial inputs from sugarcane plantations depressed coral calcification. This record provides the first pre-colonial to modern baseline for ridge-to-reef connectivity in Maui and demonstrates that historical land-use change has left a persistent geochemical imprint on the downstream reef ecosystem.

Hawaii↗
USGS2026

Cruise summary—Samoa Basin abyssal mapping—Box coring leg, Pago Pago, Territory of American Samoa to Pago Pago, American Samoa, April 11– May 1, 2026

Expedition Summary U.S. Geological Survey scientists led a box coring effort to the Samoa Basin to characterize minerals and the surrounding abyssal sediments and fauna. Thirty-eight box cores were deployed between April 13, 2026, and April 28, 2026. Thirty-six box cores recovered sufficient material to determine nodule density, and 35 recovered sufficient material for subcores to be collected. The purpose of this Data Report is to provide a summary of samples collected, initial results that were obtained shipboard, and briefly mention planned future analyses from this expedition.

Data Report↗
USGS2026

CoralCache: A virtual coral core repository for transparent and reproducible annual growth rate analyses

As science fields enter the Big Data revolution, open-access repositories are essential for addressing larger-scale questions than are possible for single researchers by making data findable, accessible, interoperable, and reusable (FAIR). Furthermore, transparent data and code are increasingly important for reproducible research, especially for data types that inherently require subjective human interpretations. These ideas are applicable to coral sclerochronology, as the field has long been characterized by individual researchers collecting and analyzing coral skeletal cores from their study sites without substantial data sharing or archiving of the core images to meet FAIR principles. Here, we present CoralCache, a virtual coral core repository that not only archives image datasets (i.e., digitized X-rays and computed tomography scans), but also observer interpretations of the density banding patterns. CoralCache is linked to a graphical user interface, CoralCT, which together offer a way forward for coral growth rate analysis that is reproducible and collaborative. The data organization systems presented here could also be readily applied to related archives such as tree rings or bivalve shells.

Earth System Science Data↗
USGS2026

The USGS Rotating X-ray Computed Tomography (RXCT) Coral-Core Archive: Scope, access, and standardization

We announce the U.S. Geological Survey (USGS) Rotating X-ray Computed Tomography (RXCT) Coral-Core Archive, a digital resource derived from ~400 coral reef cores curated at the USGS Pacific and St. Petersburg Coastal and Marine Science Centers. The archive de-livers calibrated 3-D image volumes that enable reproducible values of skeletal density, linear extension, and calcification from decadal-to-centennials scale records of coral growth and bioerosion. Cross-study comparability within the archive is supported by a unified RXCT workflow that minimizes imaging artifacts. This includes rejecting im-age-intensity–density regressions with r² < 0.95, back-calculating standard densities to verify a ±10% target precision, and confirming that band-averaged density values fall within published species- and site-specific ranges. Given global coral-reef decline and the rarity of physical archives, we release data under FAIR (Findable, Accessible, Interopera-ble, Reusable) principles. Calibrated imagery and scan metadata are distributed through CoralCache/CoralCT for analysis (DeCarlo et al., 2025), while core locations and collection metadata are published through the USGS Geologic Core and Sample Database (DOI: 10.5066/F7319TR3) with links to CT slice imagery in a USGS ScienceBase repository (DOI: 10.5066/P139Y9H4). This archive provides a powerful dataset for evaluating environ-mental controls on coral growth, establishing restoration baselines, and improving coastal-hazard assessments in the face of global coral-reef declines.

American Somoa, Guam, Florida, Hawaii, U.S. Virgin↗
USGS2026

Organic and isotopic indicators for sorting of sedimentary organic matter along a marginal submarine canyon

Submarine canyons are incised features of many continental margins that can have significant influence on the hydrodynamic distribution of sediments and organic matter eroded and deposited from the continents. Baltimore Canyon, on the mid-Atlantic margin of the United States, contains a complex set of sedimentary processes that simultaneously create unique benthic habitats and control the deposition of organic matter. Along the canyon axis, loci of net erosion, net deposition, and intense winnowing each host diverse faunal assemblages and varying mixtures of sedimentary organic matter derived both from production in the overlying water column and from mobilized sediments. Bioavailable components of this deposited organic matter sustain benthic communities, while recalcitrant components can contribute to long-term carbon burial in the deep sea. However, commonly employed bulk geochemical analyses provide little information about the relative bioavailability or depositional history of sedimentary organic matter. Here we employ a range of organic and isotopic analyses to explore in more detail how canyon-specific sediment dynamics determine the sorting of organic matter from shelf to open ocean. In combination with bulk geochemical characteristics, we subjected surface sediments from water depths of ∼200–1200 m in Baltimore Canyon to a sequential extraction procedure, isolating nonpolar and polar lipid classes, an acid-soluble fraction, and an acid-insoluble fraction. Each class was analyzed for carbon and nitrogen quantities and stable isotope ratios, and radiocarbon content where possible, along with compound-specific carbon and nitrogen isotope analysis of individual amino acids in the acid-hydrolysed fraction. We find different organic matter sources and depositional history recorded in the properties of younger, bioavailable organic matter components (polar lipids, amino acids) in comparison to the older, more recalcitrant components (nonpolar lipids, acid-insoluble fraction). These differences in source and bioavailability of organic matter vary along the canyon, correlating with grain size and erosion/deposition dynamics, and may help shape the benthic faunal assemblages. Additionally, our results suggest that determining the relative concentrations of acid-soluble and acid-insoluble organic matter may provide an easily accessible method to improve our understanding of the nutritional quality of sediments for benthic fauna than more commonly used bulk carbon or nitrogen concentrations.

Delaware, New Jersey↗
USGS2026

Samoa basin abyssal mapping: Box coring leg

This cruise report describes work from leg three of the NOAA American Samoa Abyssal Mapping effort, OPR-T900-KR-26. Leg one preceded this effort and collected ship-based acoustic data. Leg two collected autonomous underwater vehicle (AUV) data and began before, continued contemporaneously, and finished subsequently to leg three. The USGS field activity number assigned to this expedition is 2026-604-FA. The objective of this expedition was to collect representative box cores to inform prospectivity analyses through the region, and co-located interdisciplinary datasets as practical. USGS personnel directed the sampling locations and took custody of the box cores once recovered shipboard. USGS personnel then photographed and described the cores, subsampled, conducted analyses including wet weights and time sensitive measurements, and preserved subsamples and additional components for future work. Data releases co-released with this report are listed in the section “paired data releases.” NOAA released data from all legs of this effort in near-real time. Details of the preceding legs, the data, and NOAA’s project summary available from NOAA, (2026). This report is an expedition summary with preliminary datasets; remaining data releases and publications will be forthcoming.

EarthArXiv↗
USGS2025

Impact of warming and suspended terrigenous sediment on the Hawaiian reef coral Montipora capitata

Coral reefs near high human population areas suffer from sedimentation and increased turbidity due to coastal development. However, there is limited research on how key species respond to turbidity caused by terrigenous sediment and how this response may change with increased water temperatures. This study investigated the effects of ambient and elevated turbidity (+ 26 NTU) in combination with ambient (27.1 °C) and elevated temperature (+ 4.1 °C; 31.2 °C) on the dominant Hawaiian reef coral Montipora capitata , collected from two Kāneʻohe Bay watersheds with distinct environmental histories. Using intermittent flow respirometry, we found that acute (12 h) exposure to elevated turbidity and temperature impacted algal symbionts ( Symbiodinium spp. ) but not the coral host, suggesting a potential delayed host physiological response. Corals from south Kāneʻohe Bay, where restricted water circulation and urbanization have degraded water quality, were more sensitive to stressors than those from the less-impacted northern sites, indicating that physiological responses vary by location and may be influenced by watershed conditions. The findings suggest that while short-term turbidity and warming impact Symbiodinium spp. immediately, prolonged exposure may lead to cascading effects on the coral host. Understanding these species-specific and location-dependent responses enhances our ability to guide restoration and conservation efforts for coral ecosystems facing both local (turbidity) and global (warming) stressors.

Hawaii↗
USGS2025

Land-based nutrient flux to a fringing reef: Insights from Ofu Island, American Samoa

Submarine groundwater discharge (SGD) is a critical driver of nutrient transport in coral reef ecosystems, shaping water quality, primary productivity, and overall reef health. This study quantifies SGD fluxes and associated nutrient dynamics in two reef flat pools within the Ofu Unit of the National Park of American Samoa: Papaloloa and Fatuana. A multi-method approach integrating unoccupied aerial system-based thermal infrared (UAS-TIR) surveys, radon-based SGD measurements, multichannel electrical resistivity tomography (ERT), and discrete water sampling was used to assess SGD rates and nutrient contributions. UAS-TIR imagery revealed cooler sea surface temperatures in both pools, indicative of SGD, with the higher fluxes observed in Papaloloa. Radon measurements revealed a strong inverse correlation between SGD rates and tidal stage, with a more immediate SGD response at Papaloloa due to its highly permeable calcareous sand and gravel substrate. In contrast, a 2–3-hour lag in SGD response at Fatuana suggests discharge from a more inland aquifer that has lower diffusivity. Nutrient concentrations correlated with temperature and salinity, confirming SGD as the dominant nutrient transport mechanism, whereas isotopic analyses indicated inputs from both groundwater and potential anthropogenic sources. Despite lower SGD flux at Fatuana, higher algal cover suggests additional factors influencing algal proliferation, including substrate availability and hydrodynamic conditions. Excess nutrient inputs from SGD may contribute to algal overgrowth, which threatens Ofu’s thermally tolerant corals by increasing competition for space and light. These findings underscore the complexity of SGD-mediated nutrient dynamics in reef environments and emphasize the need for integrated hydrological and ecological assessments to support effective reef conservation and management strategies.

American Samoa, Ofu Island, Olosega Island↗
USGS2025

Characterizing sedimentary organic carbon in a hydrothermal spreading center, the Escanaba Trough

Sediments in critical marine mineral environments are of wide importance due to their preservation of both marine minerals and organic carbon (OC) stocks. However, OC storage and cycling is often overlooked in mineral system studies. This work characterizes sedimentary OC within the Escanaba Trough, a hydrothermal sulfide system off the coast of northern California. By utilizing ROV-based push coring, we collected sediments near and far from high temperature, low temperature, and inactive vents. We applied a multipronged organic geochemical approach, measuring bulk sediment, OC fractions of varying labilities, and biomarkers to tease apart the storage, source, and cycling of OC within this complex system. In contrast to past work indicating a primarily terrestrial source to deeper, Pleistocene sediments, our results suggest a primarily marine source in surface sediments at least 50 m away from active venting. Near active venting, we see evidence of locally produced chemosynthetic OC in addition to the background marine source. This chemosynthetic OC appears to be rapidly remineralized and supports more complex deep-sea food webs compared to hemipelagic sites. Still, the greatest contribution of labile OC was observed at inactive vent sites, which we suggest is due to hydrothermal fluid alteration of more labile OC at actively venting sites. Depending on fluid temperature, hydrothermally altered OC is either preserved in the sediments as petroleum or migrated with fluid flow. Considering inactive sites are those most likely to be targeted by potential mining, we suggest additional studies could verify if these results apply at other sedimented seafloor massive sulfide systems.

California↗
USGS2025

Factors structuring macrofaunal communities of hydrocarbon seeps along the Cascadia margin

Cold seeps, fueled by hydrocarbon-based chemosynthesis, support unique benthic communities that can vary across small spatial scales influenced by local geochemistry. We examined the community structure and function of macrofauna in cold seeps along the Cascadia margin on the edge of gas hydrate stability—a dynamic environment that may fluctuate as seafloor temperatures change. These communities were assessed in relation to their sediment environment to provide baseline data for these previously uninvestigated seeps and decipher the most significant variables structuring them. Specific environmental drivers investigated include sediment organic carbon, total nitrogen, C:N ratios, stable isotopes (δ 13 C and δ 15 N), redox potential, grain size, and porefluid chemistry. Macrofaunal community composition varied across locations separating into twelve distinct clusters. Several co-located cores clustered separately, indicating high heterogeneity in these communities at small spatial scales. Significant drivers of macrofauna communities included clay and sand content, C:N, δ 15 N values, organic carbon content, and depth. Functional trait composition was influenced by similar drivers, including depth, δ 15 N values, C:N, and sand content. Our results indicate similar environmental variables structure macrofaunal community composition and function across small- and large-scale gradients, contributing to our understanding of heterogeneity in local and regional factors that shape seep macrofaunal communities. This is the first investigation of macrofauna at these recently discovered seeps and provides baseline data on the hydrate stability zone for future comparisons, advancing our knowledge of broad-scale trends in seep macrofauna ecology.

California, Oregon, Washington↗
USGS2024

International Ocean Discovery Program Expedition 389 preliminary report: Hawaiian drowned reefs

Our understanding of the mechanisms controlling eustatic sea level and global climate changes has been hampered by a lack of appropriate fossil coral records over the last 500 ky, particularly into and out of the glacial periods. This problem was addressed by International Ocean Discovery Program Expedition 389 by drilling a unique succession of Hawaiian drowned coral reefs now at 110–1300 meters below sea level (mbsl). The four objectives are to investigate (1) the timing, rate, and amplitude of sea level variability to examine cryosphere and geophysical processes, including the assessment of abrupt sea level change events; (2) the processes that determine changes in mean and high-frequency (seasonal–interannual) climate variability from times with different boundary conditions (e.g., ice sheet size, p CO 2 , and solar forcing); (3) the response of coral reef systems to abrupt sea level and climate changes; and (4) the variation through space and time of the subsidence and the volcanic evolution of the island. To achieve these objectives, 35 holes at 16 sites ranging 131.9–1241.8 mbsl were drilled during the expedition. A total of 425 m of core was recovered, comprising reef (83%) and volcanic (17%) material. Average core recoveries were 66%, with numerous intervals characterized by very well preserved mixtures of coralgal and microbialite frameworks with recoveries >90%. Some science-critical shallow sites were not drilled due to a failure to secure permits to operate in Hawaiian state waters. Furthermore, apart from one site the target penetration depths were not achieved. Preliminary radiometric dates indicate that the recovered reef deposits are from 488 to 13 ka in age. The Onshore Science Party took place in February 2024. Cores were CT and hyperspectral scanned and described. Standard measurements were made, and samples were taken for postcruise research. Preliminary assessment of the age and quality of the reef and basalt cores suggest that many of the expedition objectives will be met.

Hawaii↗
USGS2024

Consumer isoscapes reveal heterogeneous food webs in deep-sea submarine canyons and adjacent slopes

The deep sea is the largest biome on earth, but one of the least studied despite its critical role in global carbon cycling and climate buffering. Deep-sea organisms largely rely on particulate organic matter from the surface ocean for energy – these organisms in turn play critical roles in energy transport, transformation, storage, and sequestration of carbon. Within the deep sea, submarine canyons are amongst the most complex and dynamic environments in our oceans, where varied morphology, powerful currents, and variable nutrient conditions influence the distribution of species and transport of organic material throughout the water column and the seafloor. Significant habitat heterogeneity provides ideal substrates for cold-water corals, making submarine canyons of interest to conservation and management. However, how these and other topographic features in the deep ocean influence energy flow and trophic pathways is poorly known. Thus, submarine canyons serve as model systems to track variability in organic material flux and consequential utilization and assimilation by the benthos. In this study, we used an extensive stable isotope dataset to examine food-web structure in Baltimore and Norfolk submarine canyons and compared them to their adjacent slopes located along the U.S. Atlantic margin. Linear models were used to construct geospatially-explicit consumer isoscapes that predicted variation in carbon and nitrogen isotopes across the canyon-slope seascape, providing a predictive map from which to test hypotheses on the distribution and flow of energy resources, relevant to understanding whole community function. Communities were composed of isotopically diverse feeding groups with photosynthetically-derived organic carbon providing the basal food resource. Canyon communities were distinct from the slope, with canyon consumers significantly 13 C-depleted, indicating a greater supply and/or utilization of fresh organic matter compared to the slope. Isoscapes for benthic and suspension feeders were distinct, possibly due to the consumption of different quality organic matter sources (fresh = suspension feeders, old = benthic feeders), each with distinct isotope composition. To our knowledge, our modeled isoscapes represent the first spatially extensive isotopic maps of deep-sea consumers, providing insights into regional-scale variation in stable carbon and nitrogen isotopes for different consumer groups. They provide a baseline for tracking climate-change induced fluctuations in the quality and availability of surface primary production and the consequential impact to benthic communities, which play critical roles in carbon cycling in our world’s oceans.

Progress in Oceanography↗
USGS2023

Diving deeper into seep distribution along the Cascadia Convergent Margin, USA

Previous margin-wide studies of methane seep distribution along the Cascadia Subduction Zone indicate peaks in seep density within the landward limit of the of gas hydrate stability zone (GHSZ; ≤500 m depth), suggesting a link between current ocean warming, acceleration of hydrate dissociated, and methane emissions. This inferred connection, however, may not account for regional geologic and/or structural complexities driving methane seepage. Expanding upon an existing seep database by adding new seeps data, we conducted statistical and spatial analyses to determine margin-wide distribution trends and offer a tectonic framework for understanding the tendency toward non-normality and spatial clustering. We then highlight the role of local-scale drivers of seep formation in addition to the first-order tectonic framework, using systematic geologic/geomorphic characterization of seep emission sites in southern Cascadia and case studies using meta-attribute analysis of seismic reflection data.. Seep distribution along the margin is non-random, but instead of clustering along the 500-m isobath, regions of high seep density occur in canyons and topographic highs. New findings from this study conclude that co-location of the outer arc high (OAH) and the landward limit of the GHSZ may explain high concentrations of seeps where deformation is the greatest and hydrates are unstable. Detailed analysis of the spatial relationships between seep sites and geologic-geomorphic features in southern Cascadia reveal a link between seeps and anticlines, with 52% of the seeps found in association with anticlines, 36% found at faults, 16% associated with canyons, and 11% at seafloor failure scarps. Given that a majority of anticlines are located along or seaward of the OAH in the actively deforming outer wedge, we suggest that the location of the OAH is a primary structural control on seep distribution. This scenario is supported by neural network analysis of multichannel seismic data revealing zones of probable fluid migration along vertical pipes, faults, and chimneys in the vicinity of active seep sites on anticlines. Determining linkages between seeps and submarine tectonic geomorphology is a crucial first step for understanding and forecasting the distribution of methane seepage, but also a necessity for evaluating causal relationships between ocean warming and gas-hydrate stability.

California, Oregon, Washington↗
USGS2023

A characterization of the deep-sea coral and sponge community along the Oregon Coast using a remotely operated vehicle on the EXPRESS 2022 expedition

Deep-sea coral and sponge (DSCS) communities serve as essential fish habitat (EFH) by providing shelter and nursery habitat, increasing diversity, and increasing prey availability (Freese and Wing, 2003; Bright, 2007; Baillon et al., 2012; Henderson et al., 2020). Off the U.S. West Coast, threats to these long-lived, fragile organisms from bottom contact fishing gear, potential offshore renewable energy development, and ocean warming and acidification have been the subject of recent research (Gomez et al., 2018; Salgado et al., 2018; Yoklavich, et al., 2018; Gugliotti et al., 2019). Other DSCS studies have reported new species (Yoklavich and Love, 2005), analyzed species distribution and abundance (Tissot et al., 2006, Watters et al., 2022), developed predictive distribution models (Huff et al., 2013; Rooper et al., 2017; Kreidler, 2020), and discovered medicinal uses for corals and sponges (Essack et al., 2011; Shrestha et al., 2018). Due to the vast area of unexplored seafloor within the territorial waters and the U.S. exclusive economic zone (EEZ; 12-200 nautical miles off the coast) and the technological requirements and expense of deep-sea research, there is still much to learn about the distributions and biology of DSCS. This information is critical to resource managers for effective conservation and management of DSCS habitats. In order to minimize the adverse impacts of fishing on EFH, the Pacific Fishery Management Council (PFMC) and National Marine Fisheries Service (NMFS) designated several seafloor habitat areas as EFH conservation areas (EFHCA), first in 2006 (as part of Amendment 19 to the Pacific coast groundfish fishery management plan) and then again in 2020 (as part of Amendment 28). These areas are closed to bottom trawl fishing at a minimum, and in some cases to all bottom contact fishing gears. In addition to protections afforded by EFH-related regulations, the National Marine Sanctuary Program prohibits certain non-fishing activities within areas designated as national marine sanctuaries, such as oil and gas exploration or extraction, cable laying, and other forms of seabed alteration or construction that disturb benthic communities. NOAA’s Deep-Sea Coral and Research Technology Program (DSCRTP) began a 4-yr funding initiative for the U.S. West Coast in 2017. The goals of the West Coast Deep-Sea Coral Initiative (WCDSCI) were to: 1) gather baseline information on areas subject to fishing regulation changes prior to the implementation of Amendment 28; 2) improve our understanding of known DSCS bycatch “hot spots”; and 3) explore and assess DSCS resources within NOAA National Marine Sanctuaries with emphasis on areas of sanctuary resource protection and management concerns. As part of the WCDSCU, an 11-day expedition (3 Sep – 13 Sep 2022) was launched from the NOAA Ship Bell M. Shimada, beginning and ending in Newport, OR. The science team assembled for this cruise were members of the EXpanding Pacific Research and Exploration of Submerged Systems (EXPRESS) campaign, which brings together researchers from federal and nonfederal institutions to collaborate on scientific expeditions targeting the deepwater areas off California, Oregon, and Washington. EXPRESS supports researchers leveraging funding, resources, personnel, and expertise to accomplish more science than would have been possible by a single entity alone. The 2022 expedition included research partners from National Marine Fisheries Service (NMFS) Southwest Fisheries Science Center (SWFSC) and Northwest Fisheries Science Center (NWFSC), Bureau of Ocean Energy Management (BOEM), U.S. Geological Survey (USGS), Pacific Fisheries Management Council Habitat Committee, and Woods Hole Oceanographic Institution.

Report↗
USGS2022

Pharmaceuticals and personal care products in passive samplers at seven coastal sites off West Maui, Hawaiʻi:

Passive membrane samplers—semipermeable membrane devices and polar organic chemical integrative samplers—were deployed for 22 continuous days at 7 sites along the West Maui, Hawaiʻi, coastline in February and March 2017 to assess organic contaminants at shallow coral reef ecosystems from diverse upstream inputs. The distribution of organic compounds observed at these coastal sites showed considerable variability; high concentrations of microbially sourced organic compounds observed at all sites, with pentadecane as the predominant normal alkane, showed the relative importance of marine and microbial organic matter to the coastal carbon pool. Pharmaceuticals and personal care products, as well as flame retardants, were also detected at all sites. Of the seven sites sampled, the Kahekili Beach Park site had the highest number of unique contaminants and the Honokōwai Stream site had the highest concentrations of compounds. Two individual compounds, a flame retardant and a fragrance, were ubiquitous across the studied West Maui reefs, including at the least-developed site. A direct correlation to upstream land-use practices or legacy agricultural inputs was not readily observed since polychlorinated biphenyls, pesticides, herbicides, or insecticides were not detected. Results provide a snapshot of relative contaminant abundances as well as inputs to select nearshore environments along the West Maui coastline captured during the 2017 wet season, which was drier than expected. These data can be useful for understanding the range of stressors potentially affecting nearshore ecosystems, such as groundwater inputs and watershed runoff.

Hawaii↗
USGS2022

High-resolution observations of submarine groundwater discharge reveal the fine spatial and temporal scales of nutrient exposure on a coral reef: Faga'alu, AS

Submarine groundwater discharge (SGD) can deliver substantial nutrient and contaminant loads to nearshore coral reefs. Correctly scaling SGD rates from a point source to a reef is generally a linear process involving simplified assumptions on the hydrogeology, bathymetry, and nearshore hydrodynamics that are essential to properly assess SGD scale and impact to individual coral heads. Here, we apply high-resolution SGD techniques to provide information at the scale of individual coral heads in Faga’alu Bay, American Samoa, where focused SGD delivers a plume of freshened and nutrient-rich water directly to the adjacent coral reef. Unoccupied Aerial System-based measurements were used to acquire remotely sensed, calibrated, high-resolution thermal infrared imagery that were coupled with traditional in-situ SGD observations. This approach permits a detailed assessment of SGD and associated nutrient loadings to individual coral heads as a function of time and enables a more realistic method to quantify SGD impact.

Faga’alu Bay↗
USGS2022

The role of pH up-regulation in response to nutrient-enriched, low-pH groundwater discharge

Coral reefs and their ecosystems are threatened by both global stressors, including increasing sea-surface temperatures and ocean acidification (OA), and local stressors such as land-based sources of pollution that can magnify the effects of OA. Corals can physiologically control the chemistry of their internal calcifying fluids (CF) and can thereby regulate their calcification process. Specifically, increasing aragonite saturation state in the CF (Ω CF ) may allow corals to calcify even under external low saturation conditions. Questions remain regarding the physiological processes that govern the CF chemistry and how they change in response to multiple stressors. To address this knowledge gap, the boron δ 11 B and B/Ca were analyzed in tropical corals, Porites lobata, collected at submarine groundwater seeps impacted by the release of treated wastewater in west Maui, Hawai'i, to document the interactions between high nutrient / low pH seep water on CF carbonate chemistry. Results show substantial up-regulation of pH and dissolved inorganic carbon (DIC) with respect to seawater in P. lobata corals collected from within the wastewater impacted area at Kahekili Beach Park compared to the control site at Olowalu Beach. The Ω CF was 9 to 10 times higher than ambient seawater Ω, and 13 to 26% higher than in corals from the control site and from values previously observed in tropical Porites spp. corals. Such elevated up-regulation suggests that corals exposed to nutrient-enriched, low pH effluent sustain CF supersaturated with respect to aragonite, possibly as an internal coping mechanism to combat multiple stressors from land-based sources of pollution. This elevated up-regulation has implications to coral vulnerability to future climate- and ocean-change.

Hawaii↗