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West Maui Coastal Circulation Experiment: Understanding the Movement of Sediment, Coral Larvae, and Contaminants Along Coral Reefs
From late June through mid-July, U.S. Geological Survey (USGS) scientists and technicians conducted fieldwork off West Maui, Hawai'i, to better understand coastal circulation and its effect on coral-reef health.
Led by project chief Mike Field (USGS, Santa Cruz, CA), the cruises and instrument deployments were a continuation of the USGS Coral Reef Project's research in the eight main Hawaiian Islands. This research is part of the USGS' commitment to the U.S. Coral Reef Task Force, a multiagency group, cochaired by the U.S. Department of the Interior, which was established by Executive Order in 1998 to preserve and protect the biodiversity, health, heritage, and social and economic value of U.S. coral-reef ecosystems.
The West Maui Coastal Circulation Experiment was undertaken as part of an ongoing effort led by the USGS to better understand the effect of geologic processes on coral-reef systems in the United States and its trust territories.
The USGS worked with numerous scientists from State and local agencies and organizations in its endeavor to understand the coastal circulation along West Maui, HI. While our main goals were to understand the coastal circulation's effects on the movement of sediment and contaminants, we chose the timing of the experiment to coincide with the spawning of the reef-building coral Montipora capitata, locally known as "rice coral," which was predicted to occur on the nights of June 30 through July 3.
In this way, we could also attempt to track coral larvae and determine whether the poor health of certain reefs is due to insufficient new recruitment or other environmental factors, such as excess sediment, nutrients, or contaminants. West Maui was chosen because of the wide range in health of the coral ecosystems and the importance of the reef to local residents and tourists.
Nine bottom-mounted instrument packages were deployed on June 27 and 28 by divers Mike, Curt Storlazzi (USGS, Santa Cruz), Josh Logan (USGS, Santa Cruz), Tom Reiss (USGS, Menlo Park), and Greg Piniak (USGS, Santa Cruz).
Eight of these packages measured waves, tides, currents, temperature, salinity, and optical and acoustic backscatter; they were built, tested, and programmed before deployment by Andrea Ogston (University of Washington), Dave Gonzales (USGS, Menlo Park, CA), Kathy Presto (University of Washington), Josh, and Curt.
The ninth package was Hank Chezar's (USGS, Menlo Park) "Coral Imaging System," a bottom-imaging camera designed to monitor coral-larvae and sediment dynamics. All of these packages will remain on the sea floor for 3 to 4 months to make long-term environmental measurements and, we hope, to image different coral species' spawning events later in the summer.
Each day during the coral spawning, USGS and University of California, Santa Cruz (UCSC), scientists used a converted fishing vessel, the Alyce C, to conduct hydrographic surveys in order to get a better spatial view of the processes and environmental parameters being recorded by the bottom-mounted instruments.
Margaret McManus (UCSC), Brian McLaughlin (UCSC), Josh, and Curt collected more than 11 km of vessel-mounted acoustic Doppler current-profiler (VM-ADCP) data and 20 conductivity-temperature-depth/optical-backscatter (CTD/OBS) profiler casts each day during the spawning event.
They were joined on different days by Greg Piniak, who conducted larval tows to collect coral-larvae samples, and Jodi Harney and Eric Grossman (USGS, Santa Cruz), who collected laser-in-situ-scattering-and-transmissometry (LISST) data by attaching the LISST sensor to the CTD/OBS profiler.
We hope that the larval tows and LISST data will permit us to calibrate the OBS' optical backscatter and VM-ADCP's acoustic backscatter so that we can use the VM-ADCP data to map the concentration and spatial distribution of coral larvae.
In an attempt to better understand water-mass and coral-larvae movement, radio-trackable differential-GPS (DGPS) drifters were deployed over a healthy reef each night when the coral larvae spawned at about 9:00 p.m. local (Hawai'i standard) time. These drifters, which were designed and built by Tom Reiss (USGS, Menlo Park), present minimal area to the wind and are moved instead by currents pushing against plastic fins, called "drogues," that can be mounted on the bottom of a drifter to measure currents at the surface or on a line attached to the drifter to measure currents below the surface.
Gerry Hatcher (USGS, Santa Cruz) designed and fabricated the electronics placed inside each drifter, which transmitted the DGPS signal via radio so that Gerry and Tom could track all of the drifters from a base station onshore. The drifters transmitted their coordinates either directly to the base station in Gerry and Tom's hotel room or first to repeaters set up on the neighboring islands of Lanai and Molokai.
Using geographic-information-system (GIS) software, Gerry and Tom were able to track and map the drifters' positions in real time, permitting USGS or cooperating personnel to recover them. Each night, two sets of two drifters, with one of each set drogued for surface currents and the other drogued for currents 3 to 5 m below the surface, were deployed from boats by Tom and Mike. Tom, Gerry, and Mike then allowed them to drift until they came ashore or made their bid for freedom out to sea. Personnel from the University of Hawai'i, the Maui Division of Aquatic Resources, Maui Community College, the U.S. Coast Guard, and the Maui Division of Ocean and Boating Recreation helped during the planning, permitting, deployment, and recovery of the drifters.
Greg and biologists Eric Brown (University of Hawai'i's Institute of Marine Biology), Donna Brown (Maui Community College), Alan Ligon (University of Hawai'i's Institute of Marine Biology), John Gorman (Maui Ocean Center), and Erica Cushing (Maui Ocean Center) collected data on the coral larvae and their recruitment success at several locations in the study area, most of which were co-located with the USGS' bottom-mounted instruments. This co-location will help us determine whether specific environmental factors (wave-induced stresses, temperature, salinity, and so on) are responsible for recruitment success at any given location.
In a goodwill gesture, the biologists attempted, albeit rather unsuccessfully, to teach "rockhead" geologists Mike, Tom, Josh, Eric, and Curt how to identify and count coral larvae during scuba dives at night when the corals were spawning.
We wish to thank Captain Joe Reich of the Alyce C, who was outstanding as usual in his support of the boat surveys, instrument deployments, drifter recoveries, and scuba operations. Thanks also to Eric Brown, who, in the middle of trying to write the last of his Ph.D. thesis (which will likely become "THE" book on Maui reefs), took on the extremely difficult and time-consuming task of coordinating the State and local agencies that contributed people, boats, and vehicles to the experiment.
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