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USGS Leads Field Trip for Attendees at U.S. Coral Reef Task Force Meeting
During the fall 2014 meeting of the United States Coral Reef Task Force (USCRTF), held in Kāʻanapali, Maui, Hawaiʻi, Curt Storlazzi of the U.S. Geological Survey (USGS) Pacific Coastal and Marine Science Center (Santa Cruz, California) led a field trip along the west Maui coast to address the science behind the “Past, Present, and Hopefully Future of Maui’s Coral Reefs.”
The goal of the field trip was to provide participants with an overview of more than 15 years of integrated scientific investigations by federal, state, academic, and non-governmental organization (NGO) scientists to identify land-based sources of pollution from the Wahikuli and Honokōwai watersheds—primarily eroded sediment, nutrients from agricultural fertilizers, and nutrients and contaminants from discharged wastewater—and document the resulting impact on the adjacent fringing coral reefs. These watersheds have been designated as a USCRTF priority study site, underscoring their importance in the “ridge to reef” concept of marine ecosystem health.
The nearly 50 field-trip participants represented a broad range of organizations, including the U.S. Department of the Interior, National Oceanic and Atmospheric Administration (NOAA), Environmental Protection Agency (EPA), U.S. Army Corps of Engineers, U.S. Fish and Wildlife Service, National Aeronautics and Space Administration (NASA), State of Hawaiʻi Division of Aquatic Resources, Hawaiian Islands Humpback Whale National Marine Sanctuary, Scripps Institution of Oceanography, University of Hawaiʻi, and National Coral Reef Institute, along with interested members of the public. At both stops on the field trip, participants were briefed on the scientific issues and history of research at the site, including geologic and oceanographic controls of sediment, nutrient, and contaminant influx to the coral reefs, as well as how recent management efforts have begun to mitigate the impacts of these land-based pollutants. Discussions were followed by a snorkeling tour of the nearshore reefs.
The field trip started on Kapua Beach, located in Kahana at the very northern edge of the Honokōwai watershed, where Storlazzi described the legacy of 150 years of pineapple cultivation and other causes of upland erosion, and explained how sediment delivered to the coast has resulted in a shift from clear water and a healthy coral reef system to a nearshore environment with cloudy water and a veneer of mud on the reef and surrounding seafloor. He discussed how previous research by University of Hawaiʻi ecologists motivated the USGS Pacific Coral Reef Project, in the 2000s, to focus its investigations on circulation and sediment dynamics in this area. Those USGS studies resulted in numerous scientific journal articles and USGS reports that advanced our understanding of how sediment moves through fringing coral reefs and provided data for scientists and managers. (For an overview of these studies, see http://coralreefs.wr.usgs.gov/maui.html.) While snorkeling, the field trip participants could see the abundance of algae, a muddy seafloor with little live coral, and few reef fish.
At the second stop at Kahekili Beach Park, located along the central coast of the Wahikuli watershed, Storlazzi and Darla White (State of Hawaiʻi, Division of Aquatic Resources) discussed the history of research into the impact of nearby wastewater injection wells on the coral reefs. These studies began in the late 1990s with inconclusive EPA investigations on algal overgrowth of the reefs, followed by successful studies by the University of Hawaiʻi linking the algal overgrowth to nutrients in the wastewater. The USGS Pacific Islands Water Science Center followed with an observational study and numerical modeling that showed how the plume from the Lahaina Wastewater Reclamation Facility flows underground to the coast; this prompted the USGS Pacific Coral Reef Project’s high-resolution seafloor mapping and studies of physical and geochemical processes to understand the rates, volumes, and ultimate fate of constituents being discharged through the reef. Lastly, Storlazzi and White discussed the recent success of the State of Hawaiʻi Kahekili Herbivore Fisheries Management Area (established in 2009), which has improved the health of the coral reef by increasing the number of herbivores (plant eaters) that consume the algae growing on the corals because of the introduction of wastewater nutrients. During the underwater tour, participants were able to view nearshore submarine vents issuing nutrient- and contaminant-laden groundwater and nitrogen bubbles from the onshore injection wells, as well as erosion of the reef rock around these vents. A short swim northward, away from the vents, allowed the snorkelers to view a healthy coral reef, with an abundance of live coral, many reef fish, and little algae. After seeing the effects of erosion and sedimentation—the “Past”—and wastewater discharge—the “Present”—the participants ended the day with this vision of the “Hopeful Future.”
Feedback from field-trip participants was positive and discussions were lively. Much of the talk centered on what the next steps should be to ensure the future of west Maui’s coral reefs. Many asked, “What should we do?” What was clear to all was the volume and breadth of the science that helps guide restoration efforts in this USCRTF Priority Study Area, and that the USGS continues to play a leading role in providing the basic and applied science on land-based pollution necessary to achieve these goals.
For further information see:
Cochran, S.A., Gibbs, A.E., and White, D.J., 2014, Benthic habitat map of the U.S. Coral Reef Task Force Watershed Partnership Initiative Kāʻanapali priority study area and the State of Hawaiʻi Kahekili Herbivore Fisheries Management Area, west-central Maui, Hawaiʻi: U.S. Geological Survey Open-File Report 2014–1129 (http://dx.doi.org/10.3133/ofr20141129).
Storlazzi, C.D., and Field, M.E., 2008, Winds, waves, tides, and the resulting flow patterns and fluxes of water, sediment, and coral larvae off West Maui, Hawaiʻi: U.S. Geological Survey Open-File Report 2008–1215 (http://pubs.usgs.gov/of/2008/1215/).
Swarzenski, P.W., Storlazzi, C.D., and others, 2012, Nearshore morphology, benthic structure, hydrodynamics, and coastal groundwater discharge near Kahekili Beach Park, Maui, Hawaiʻi: U.S. Geological Survey Open-File Report 2012–1166 (http://pubs.usgs.gov/of/2012/1166/).
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