Integrated Ecosystem Studies Underway off the Kona Coast of the Island of Hawaii
The NOAA Ship Oscar Elton Sette is on a 14-day research cruise in waters off the Kona coast of the Island of Hawaii. The expedition will provide support for the Pacific Islands Fisheries Science Center's (PIFSC) Integrated Ecosystem Assessment (IEA) project in the Kona region, also known as West Hawaii. The main goal of the Kona IEA cruise is to learn about the characteristics and functioning of the ecosystem, including physical and chemical features of the ocean waters and the biology of marine organisms living in the area. The scientific field party includes researchers from PIFSC, The University of Hawaii (UH), the Joint Institute for Marine and Atmospheric Research (JIMAR), and the American Museum of Natural History. Chief Scientist for the expedition is Evan Howell, a research oceanographer at the PIFSC.
An additional goal of the research cruise is to provide experience and training for future scientists. Accordingly, the field party will include an undergraduate student from the UH, a graduate student from the UH School of Ocean and Earth Science and Technology, an undergraduate PIFSC summer intern, two undergraduate recipients of NOAA Ernest F. Hollings scholarships, and a NOAA Teacher at Sea.
The mission of the cruise is to better understand spatial ecosystem differences off the West Hawaii coastline. Ecosystem information collected during the survey will help identify north-south or onshore-offshore differences that may be present during the cruise. Researchers will survey the "Kohala Shelf" area between the islands of Hawaii and Maui, which appears to be a center of activity for some cetacean species. A question they want to answer is how this region may differ from the offshore waters south of Keahole point. The team will also will study another spatial ocean feature of interest in the region, the local (mesoscale) eddies that are generated by a combination of topography and prevailing northeasterly tradewinds. Scientists want to know how the eddies may affect different components of the ecosystem off West Hawaii, from plankton and smaller organisms up through the larger fishes, cetaceans and other marine life in the area.
The research vessel departed Ford Island, Pearl Harbor, on July 1, 2011 and traveled to the Kona coast waters to begin oceanographic operations. Initial operations will occur at specific locations (stations) along the Kohala Shelf area to try and identify offshore-onshore changes in water properties and biological characteristics across the Kohala Shelf to the north. Once sampling across the shelf region is completed, the Sette will move south and commence operations along two north-south transects. There, the research team will to try to identify any ecosystem changes along this spatial gradient and determine if they are consistent between the offshore transects and the transects closer to the West Hawaii coastline.
Model forecasts of ocean physical properties for July 2011 show that a large ocean eddy (a mesoscale feature) may be present in the Kona area. Several research projects in the past have described the physical features and biological responses of the eddies and on this cruise we hope to gain additional knowledge about these important oceanic features.
To obtain as much information as we can about the West Hawaii oceanic ecosystem, we will measure parameters of as many layers of the ecosystem as possible during the two-week cruise. At each station, we will measure the physical, chemical, and biological characteristics of the ocean using several techniques. We will measure the physical characteristics of the ocean using an instrument called a CTD profiler. The CTD profiler sensors measure the conductivity, temperature, and pressure of the surrounding water as the profiler is lowered from the ocean surface down through the water column to our maximum defined survey depth of 1000 meters. We will also measure ocean currents continuously using an Acoustic Doppler Current Profiler (ADCP), enabling us to determine how fast water is moving across an entire water column. We will measure ocean chemistry through a combination of at-sea and laboratory techniques. Oxygen concentrations in the water column will be measured by using an oxygen sensor affixed to the CTD profiler. During each CTD profile operation (or cast), water samples will be collected at 12 standard depths using 10-liter Niskin bottles. The bottles are deployed on the CTD instrument with both ends open; at the desired depth, they are remotely triggered to close, capturing a discrete water sample. The bottled samples are filtered at sea to measure biological properties or stored for later analysis in the laboratory. Thirty milliliters of water will be taken from each collection bottle and immediately frozen for later analysis of nutrient concentrations. Taken together, these sample water measurements will provide key information on the physics and chemistry of the West Hawaii marine ecosystem during the cruise.
To estimate the abundance of phytoplankton in the water column and identify phytoplankton classes, an additional three liters of water will be taken from each Niskin bottle and filtered in the wet laboratory of the Sette. Although phytoplankton densities are continuously estimated during each CTD cast using a fluorometer attached to the CTD instrument, several factors may introduce errors in the estimates. So it is important to spot check or "truth" the CTD fluorometer estimates using a stable, tested laboratory technique. In the ship's laboratory, one liter of water will be filtered for analysis of chlorophyll-a using The Turner 10AU field fluorometer. This will provide a gross estimate of the abundance (standing stock) of phytoplankton off West Hawaii during the cruise. To understand the phytoplankton class composition, two liters of water will be filtered and the resulting samples frozen in liquid nitrogen for later laboratory analysis at the University of Hawaii. These results will provide information on the primary level of the ecosystem food chain.
To study animals in the next higher level of the ecosystem food web, we will use active acoustic techniques, or sonar. We will deploy a bioacoustic instrument to measure the abundance and distribution of marine organisms in the water column. The instrument emits pulses of sound downward from the ship's hull, then records echoes of the sound waves reflected back to the ship. The return waves are created as the downward sound pulses encounter organisms in the water. By studying the echoes, or "backscatter", the researchers learn to identify the kind of organisms present and their size and biomass density. Analysis of backscatter data reveals patterns of distribution and movement of the encountered marine life. Organisms encountered include small fish, squid, and shrimp that make up the so-called "sound scattering layers" (SSL) and are important food for larger fish in the ecosystem.
To improve the accuracy of organism identification based on the acoustic system, Sette researchers will collect samples of organisms from the scattering layers at night using a large trawl net towed from the ship. The trawl net will be deployed to different depths, with target depths identified by the bioacoustic survey results. Collected trawl samples will be examined to determine what kinds of organism are present and take measurements of the organisms. These results will then be combined with the measured acoustic data in order to improve the accuracy and effectiveness of acoustic monitoring.
Cetacean specialists will collect information on whales and dolphins throughout the cruise. While the Sette is underway, observers stationed on the ship's flying bridge will scan the sea surface looking for cetaceans using 25x150 "big-eye" binoculars. When they encounter a group (pod) of cetaceans, they will identify the species involved and record data on the size of the pod and its behavior. In addition, while the Sette is "on station" to collect the other oceanographic and biological data, teams of 4 scientists will be deployed in the Sette's 17' safe boat to collect cetacean observations.
Through a combination of these ecosystem measurements, PIFSC hopes to gain a complete ecosystem "snapshot" assessment of the West Hawaii oceanic region. The various methodologies should provide information on each of the ecosystem levels, and the repetition of the methods at survey stations along the Kohala Shelf and the coast of West Hawaii should provide enough information to spatially define, compare and contrast important ecosystem features.