Resources & Links

Research Studies in R2R Watersheds & Relevant Links

Declines in tourism during COVID-19 reduces nitrogen loading of groundwater input to a coral reef in West Maui, Hawaiʻi

https://doi.org/10.1016/j.marpolbul.2025.118502
The coral reef at Kahekili Beach Park (KBP) in West Maui receives eutrophic submarine groundwater discharge (SGD), of which over half is injected wastewater from the Lahaina Wastewater Reclamation Facility (LWRF). Algal blooms, decreased calcification, calcium carbonate dissolution and bioerosion have been identified as consequences of injected wastewater. During the COVID-19 pandemic, Maui visitor numbers dropped 99 %, which reduced effluent volume and total nitrogen (TN) loading of injected wastewater by 70 % and 60 %, respectively. Water samples were collected at KBP during and after the visitor quarantine to characterize SGD nitrate concentrations ([NO3−]) during changing visitor population and injected wastewater characteristics. These results reveal a > 99 % reduction of SGD [NO3−] at the height of the visitor quarantine and suggest that TN injected at the LWRF should be kept below ∼53 lbs. d−1, which is more than four times the limit outlined in the LWRF National Pollutant Discharge Elimination System draft permit.
Andrea K. Kealoha, Kathryn E.F. Shamberger, Christopher K. Shuler, Samantha McClain, Tova Callender, Russell Sparks

Observations of Coastal Circulation, Waves, and Sediment Transport along West Maui, Hawaiʻi , and Modeling Effects of Potential Watershed Restoration on Decreasing Sediment Loads to Adjacent Coral Reefs

Open file report 2022-1121
Terrestrial sediment discharging from watersheds off West Maui, Hawaiʻi, has been documented as a primary stressor to local coral reefs, causing coral reef health to
decline. The U.S. Geological Survey acquired and analyzed physical oceanographic and sedimentologic field data off the coast of West Maui to calibrate and validate physics-based,
numerical hydrodynamic and sediment transport models of the study area developed by Deltares. These models simulated terrestrial sediment transport and dispersal from West Maui watersheds into coastal waters and how terrestrial sediment affects nearby coral reefs under different oceanographic forcing and watershed restoration scenarios.
Storlazzi, C.D., Cheriton, O.M., Cronin, K.M., van der Heijden, L.H., Winter, G., Rosenberger, K.J., Logan, J.B., and McCall, R.T., 2023, Observations of coastal circulation, waves, and sediment transport along West Maui, Hawaiʻi (November 2017–March 2018), and modeling effects of potential watershed restoration on decreasing sediment loads to adjacent coral reefs: U.S. Geological Survey Open-File Report 2022–1121, 73 p., https://doi.org/10.3133/ofr20221121.

Sediment Budget for Watersheds of West Maui, Hawaii

Story Map Summary here
Scientific Investigations Report 2020–5133:
Episodic runoff brings suspended sediment to West
Maui’s nearshore waters, turning them from blue to brown.
This pollution degrades the ecological, cultural, and
recreational value of these iconic nearshore waters. We used mapping, monitoring, and modeling to identify and quantify the watershed sources for fine sediment that pollutes the nearshore each year. These results focus strategies to reduce pollution on the outstanding sources for this sediment.
Terrestrial runoff causing coastal plumes now occurs
when two or more hours of rain falls at rates greater than
10–20 millimeter (mm) per hour in source watersheds.
Analysis of recent and historical rainfall indicates that West
Maui communities can expect rainfalls to bring coastal plumes
at least 3–5 times per year. Former agricultural fields and some
unimproved roads are possible sources for the fine sediment
of these plumes. We found, however, that these obvious
sources do not produce plumes during small annual storms,
because they drain water at rates that far exceed most annual
rainfalls and because there is no evidence for runoff from
rains that caused recent plumes. Streambanks now eroding
into historic fill terraces of sands, silts, and clays are a more
plausible source. These terraces are found only downstream
of historical agricultural fields and are composed of silt and
fine sand. Surveys show that the fill terraces occupy ~40
percent of streambank length, making them extensive. During
2015–2016, these deposits eroded at median rates of 5–24
mm per year. Summed over West Maui’s watersheds, these
rates imply sediment loads carried to the coast that can be ten
times or more than modeled pre-human values. A sediment
budget indicates that bank erosion of fill terraces from a
few watersheds likely dominates the current annual fine sediment load to the nearshore, with Kahana Stream watershed
producing the largest annual input of 285 metric tons, the
equivalent of 29 dump-truck loads every year.
Although past large storms have contributed to sediment
loading, annual plume generation is now caused by smaller
rainfalls eroding these near-stream terrace deposits, a legacy
of historic agriculture. Treatments of former agricultural
fields, roads, and reserve forests are consequently not likely
to measurably effect sediment pollution from smaller, more
frequent storms. Increased runoff from residential and
commercial development of West Maui has the potential to
exacerbate sediment plumes from such storms.
Stock, J.D., and Cerovski-Darriau, Corina, 2021, Sediment budget for watersheds of West Maui, Hawaii: U.S. Geological Survey Scientific Investigations Report 2020–5133, 61 p., 1 plate, scale 1:25,000, https://doi.org/10.3133/sir20205133.

The Atlas of the Reefs of West Maui

Released March 2020: The Nature Conservancy released the “Atlas of the Reefs of West Maui,” a comprehensive report compiling 20 years of data detailing changes in the abundance and diversity of marine life in West Maui. The ‘first-of-its-kind’ atlas includes data collected by public and private organizations at 2,600 sites stretching from the “Pali” Tunnel on Honoapiʻilani Highway to Līpoa Point north of Honolua Bay.
Citation: Minton, D., Carr, R., Fielding, E., & Conklin, E. 2020. Atlas of the Reefs of West Maui. The Nature Conservancy Hawai‘i. Honolulu, HI 97817. 228 pp.

Maui-area coral reefs described in detail, including threats

Released July 1, 2019
A new USGS Open-File Report describes the coral reefs of Maui, Moloka‘i, Lānaʻi, and Kahoʻolawe in detail, including location, extent, coral cover, and connectivity.
The nine major coral reefs surrounding Maui and three nearby Hawaiian Islands (collectively Maui Nui) are critical to the local ecology, culture, and economy. Reef health has slowly declined over decades, and recent events such as the 2015 thermal bleaching have accelerated reef loss significantly, in some areas by an order of magnitude. The publication also describes threats to reef health, including overfishing, land-based pollution, and climate change. The report provides information that could inform Federal and State governments in their effort to establish a network of large-scale, connected Marine Protected Areas for effective management and protection of coral reefs in Hawai’i.
Citation: Field, M.E., Storlazzi, C.D., Gibbs, A.E., D’Antonio, N.L., and Cochran, S.A, 2019, The major coral reefs of Maui Nui, Hawai‘i—Distribution, physical characteristics, oceanographic controls, and environmental threats: U.S. Geological Survey Open-File Report 2019–1019, 71 p., https://doi.org/10.3133/ofr20191019.

Baseline Assessment for Coral Reef Community Structure and Demographics on West Maui

Detailed assessment of coral condition in West Maui to provide baseline for understanding changes in coral health that may result from mitigation actions by R2R
Released Spring 2017
Citation: Baseline assessments for coral reef
community structure and demographics on west Maui. Data Report. NOAA Fisheries Pacific Science Center, PIFSC Special Publication, SP-17-001, 44p.

Pharmaceuticals and Personal Care Products in Passive Samplers at Seven Coastal Sites off West Maui, Hawai‘i

Open-File Report 2022–1065
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, 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.
Campbell, P.L., Prouty, N.G., and Storlazzi, C.D., 2022, Pharmaceuticals and Personal Care Products in Passive Samplers at Seven Coastal Sites off West Maui, Hawai‘i: U.S. Geological Survey Open-File Report 2022–1065, 12 p., https://doi.org/10.3133/ofr20221065.

Rigorously Valuing the Role of U.S. Coral Reefs in Coastal Hazard Risk Reduction

Open-File Report 2019-1027
Prepared in cooperation with the University of California Santa Cruz and The Nature Conservancy

The degradation of coastal habitats, particularly coral reefs, raises risks by increasing the exposure of coastal communities to flooding hazards. The protective services of these natural defenses are not assessed in the same rigorous economic terms as artificial defenses, such as seawalls, and therefore often are not considered in decision making. Here we combine engineering, ecologic, geospatial, social, and economic tools to provide a rigorous valuation of the coastal protection benefits of all U.S. coral reefs in the States of Hawaiʻi and Florida, the territories of Guam, American Samoa, Puerto Rico, and Virgin Islands, and the Commonwealth of the Northern Mariana Islands. We follow risk-based valuation approaches to map flood zones at 10-square-meter resolution along all 3,100+ kilometers of U.S. reef-lined shorelines for different storm probabilities to account for the effect of coral reefs in reducing coastal flooding. We quantify the coastal flood risk reduction benefits provided by coral reefs across storm return intervals using the latest information from the U.S. Census Bureau, Federal Emergency Management Agency, and Bureau of Economic Analysis to identify their annual expected benefits, a measure of the annual protection provided by coral reefs.
Citation: Storlazzi, C.D., Reguero, B.G., Cole, A.D., Lowe, E., Shope, J.B., Gibbs, A.E., Nickel, B.A., McCall, R.T., van Dongeren, A.R., and Beck, M.W., 2019, Rigorously valuing the role of U.S. coral reefs in coastal hazard risk reduction: U.S. Geological Survey Open-File Report 2019–1027, 42 p., https://doi.org/10.3133/ofr20191027.

Assessing the Resilience of Leeward Maui Reefs to Help Design a Resilient Managed Area Network

Released March 2019
The project team assessed the relative resilience of reef sites at two depths along areas of West and South-West Maui ("leeward Maui") in March of 2018. The surveys were conducted as a collaborative effort with DAR, The Nature Conservancy, and community organizations. This report presents findings from meeting these project objectives: 1) assess benthic cover comparisons among sites and depths, 2) complete resilience assessment including relative resilience and rankings for two depths, 3) conduct analyses that determine the primary drivers of differences in resilience between sites, and 4) develop a framework for using the resilience analysis outputs to identify and prioritize potential management actions to support the resilience of coral reefs in Maui. Two page summary available here.
Citation: Maynard J, Conklin E, Minton D, Williams GJ, Tracey D, Amimoto R, Carr R, Fielding E, Lynch H, Rose J, Sparks R, Sylva R, White D. (2019). Assessing the Resilience of Leeward Maui Reefs to Help Design a Resilient Managed Area Network. NOAA Coral Reef Conservation Program. NOAA Technical Memorandum CRCP 33, 40 pp.

The Use of Passive Membrane Samplers to Assess Organic Contaminant Inputs at Five Coastal Sites in West Maui, Hawaii
Released July 2017

Coral Reef Recovery Plan, Department of Aquatic Resources
Released March, 2017

Modeling Fine-Scale Coral Larval Dispersal and Interisland Connectivity to Help Designate Mutually-Supporting Coral Reef Marine Protected Areas: Insights from Maui Nui, Hawaii

Kahekili Reef Studies

2018 Update: Kahekili Herbivore Fisheries Management Area

Coral Skeleton δ15N as a Tracer of Historic Nutrient Loading to a Coral Reef in Maui, Hawaii

Excess nutrient loading to nearshore environments has been linked to declining water quality and ecosystem health. Macro-algal blooms, eutrophication, and reduction in coral cover have been observed in West Maui, Hawaii, and linked to nutrient inputs from coastal submarine groundwater seeps. Here, we present a forty-year record of nitrogen isotopes (δ15N) of intra-crystalline coral skeletal organic matter in three coral cores collected at this site and evaluate the record in terms of changes in nitrogen sources. Our results show a dramatic increase in coral δ15N values after 1995, corresponding with the implementation of biological nutrient removal at the nearby Lahaina Wastewater Reclamation Facility (LWRF). High δ15N values are known to be strongly indicative of denitrification and sewage effluent, corroborating a previously suggested link between local wastewater injection and degradation of the reef environment. This record demonstrates the power of coral skeletal δ15N as a tool for evaluating nutrient dynamics within coral reef environments.
Murray, J., Prouty, N.G., Peek, S. et al. Coral Skeleton δ15N as a Tracer of Historic Nutrient Loading to a Coral Reef in Maui, Hawaii. Sci Rep 9, 5579 (2019). https://doi.org/10.1038/s41598-019-42013-3

Characterization of dead zones of Porites compressa along Kahekili Beach Park Kahekili Beach Park in Kaanapali, Maui, was selected as the study site based on the 40% loss of coral coverage documented through DAR/CRAMP monitoring from 1995 to 2005, recent evidence that sewage effluent is being introduced to the reef via injection wells, and observations of areas of discrete areas of nearly 100% loss in coral cover known as “dead zones”. “Dead zones” are characterized by low coral cover with high abundance of standing but dead coral skeleton. Low coral coverage alone is not necessarily indicative of degradation. The presence of standing but dead skeleton and rubble suggest that live coral coverage used to be present but has been degraded through historical mortality events.
Ross et.al 2012.

Mapped Products

The West Maui Coastal Uses Participatory Mapping Project was conducted as a partnership of DAR, NOAA PIRO and NOAA PSC. The project has mapped significant human uses (including range and intensity) of the nearshore area to inform resource management. See maps of where people are fishing, jet skiing, surfing and many other uses in an interactive format.

Detailed maps of West Maui Reefs from the Pacific Islands Benthic Habitat Mapping Center

West Maui Wahikuli and Honokōwai Priority Watershed Area
REEF CONDITION REPORT 2016

Guidance for Watershed Managers

Watershed Stewardship

Created in 1997 through the community based West Maui Watershed Management Advisory Committee is the West Maui Watershed Owners Manual. Despite the changes to our land use patterns and environmental challenges since its release, this guide written for the community still contains highly relevant advice about actions anyone living, working or playing in West Maui can take to make a positive difference. This was funded by the DOH, USEPA and NOAA.

The US Coral Reef Task Force Watershed Working Group Metrics Subcommittee has developed metrics guidance documents to assist with what parameters are important for watershed managers to collect to track progress. The priority Ecosystem Indicators include water quality and coral metrics, while the Programmatic Checklist focuses on the non-ecological factors that play into success, such as institutional support, a watershed management plan, local governmental support etc.

This tool was created to assist watershed managers to more effectively link watershed assessments and management planning with coral ecosystem restoration and conservation.

Links to Partner Agencies & Organizations

NOAA Coral Reef Program: http://coralreef.noaa.gov/
DLNR Department of Aquatic Resources: http://www.hawaiicoralreefstrategy.com/
U.S. Army Corps of Engineers: http://www.poh.usace.army.mil/
Hawaii State Department of Health: http://health.hawaii.gov/
U.S. Environmental Protection Agency: http://www.epa.gov/
U.S. Geological Survey: http://www.usgs.gov/
U.S. Fish and Wildlife Service: http://www.fws.gov/
National Fish and Wildlife Foundation: http://www.nfwf.org/coralreef/Pages/home.aspx#.U8SnrrHCd8E
Hui O Ka Wai Oka: https://www.huiokawaiola.com/
West Maui Mountains Watershed Partnership: http://www.westmauiwatershed.org/
The Nature Conservancy: http://www.nature.org
The Coral Reef Alliance: http://www.coral.org/
County of Maui: http://www.co.maui.hi.us/
Maui Nui Marine Resource Council: http://www.mnmrc.org/

The USGS Pacific Coastal & Marine Science Center has conducted considerable research in West Maui on topics such as coral larval dispersal, coastal circulation and sedimentation patterns, the impact of sediments and much more. Check out the link dedicated to work on Maui.
http://coralreefs.wr.usgs.gov/maui.html