Sea Technology

SEP 2012

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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AUVs for Ecological Studies Of Marine Plankton Communities Intelligent Algorithms on Dorado and Tethys AUVs Enable Precise Water Sampling for Plankton Research By Dr. Julio Harvey Research Technician, Research and Development Dr. Yanwu Zhang Senior Research Specialist and Dr. John Ryan Senior Research Specialist Monterey Bay Aquarium Research Institute Moss Landing, California M arine plankton are central to processes sustaining life on Earth. For example, as primary producers, they regulate atmospheric gases, and phyto- and zooplankton, which occupy the lowest trophic levels, fuel marine food webs, supporting larger organisms, including economically important species for fisheries around the world. Coastal plankton communities exhibit widespread spa- tial and temporal variation in abundance, diversity and be- havior. These variations are often in response to similarly variable shifts in local environmental processes, both physi- cal (e.g., wind-driven circulation and mixing) and chemical (e.g., nutrient influxes from upwelling, riverine or other ter- restrial outflow sources). Traditional methods, like tow-netting, are invaluable for documenting overall plankton community diversity and continue to provide comprehensive data sets. These efforts, however, have also revealed that advancing plankton ecolo- gy studies requires precise methods to sample spatially and temporally variable plankton communities. High-precision sampling methods have made it pos- sible to identify invertebrate larvae transported in sediment plumes, phytoplankton concentrated into thin layers and zooplankton collected against steep density gradients gen- erated by upwelling fronts. These accomplishments address the paramount ecological issues of population connectivity and effective planning of marine protected areas, harmful algal bloom development and monitoring, and upwelling mediated production and aggregation of zooplankton, in- cluding local invertebrate larval retention and supply. Because a single method of observation cannot compre- hensively describe the complex and dynamic interplay be- tween coastal oceanic processes and biological outcomes, multiscale, multidisciplinary experiments are necessary. Such experiments simultaneously deploy multiple ocean- (Right) The Monterey Bay Aquarium Research Institute's AUV Dorado, with Gulper midsection cover removed. (Left) The Gulper water sampling mechanisms. observing assets, including moorings, ships, drifters, gliders, AUVs, autonomous in-situ water sample analyzers and re- mote sensing instrumentation. The resulting data sets enable insights into complex ecological relationships. Dorado AUV The Monterey Bay Aquarium Research Institute's (MBARI) Dorado AUV combines synoptic environmental data acqui- sition, high-intake-rate water sampling and adaptive deci- sion-making software to collect plankton at fine spatial and temporal scales. The Dorado is outfitted with a suite of sen- sors measuring temperature, salinity, nitrate, oxygen, chloro- phyll fluorescence, optical backscattering, bioluminescence and particle-size distribution, as well as 10 Gulper water samplers. The sensors' measurements reveal a synoptic view of water-column properties along the vehicle's sawtooth- shaped flight path and are precisely associated with each of the 10 water samples collected during an AUV mission. When triggered to fire by the AUV's decision-making software, each spring-loaded sampler collects 1.8 liters of seawater in less than two seconds through ports in the hull of the vehicle and stores these samples for analysis upon return to shore. The rapid sample intake is designed to break through the boundary layer formed by passage of the ve- www.sea-technology.com SEPTEMBER 2012 / st 51

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