MRI: Development of an integrated wide-band acoustical backscattering and large-area camera imaging instrument for studies of mesopelagic and bathypelagic ecosystems

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

The mesopelagic and bathypelagic zones together span ocean depths from approximately 200 meters to 4,000 meters below the surface and form one of the largest habitats on Earth. These zones are home to diverse communities of zooplankton and micronekton, including a variety of small fishes, cephalopods, crustaceans, and gelatinous organisms. Yet relatively little is known about the biology, adaptations, abundance, biomass, and distribution of the inhabitants of these deep and dark ecosystems. In general, such organisms are difficult to sample by conventional nets due to a combination of the patchiness of the organisms, avoidance of the nets by more mobile organisms, difficulties in sampling synoptically at such depths using nets, and the destruction of fragile species by the nets. However, recent evidence suggests that the global biomass estimates of micronektonic fish in the mesopelagic zone based on sampling by nets may be an order of magnitude too low and suggests a strong coupling between surface production and mesopelagic fish biomass, hinting at a previously under-appreciated biogeochemical role. This project will fill the current technological void for characterizing mesopelagic and bathypelagic ecosystems by developing a combined acoustical and optical ecosystem assessment instrument for quantifying the biomass and distribution of zooplankton and micronekton in the mesopelagic and bathypelagic zones. This instrument is particularly well suited to understanding the diverse communities of zooplankton and micronekton in relation to environmental variability, such as meso-scale oceanic eddies, fronts, and upwelling regions, and abrupt topography, such as canyons, seamounts, and shelf breaks. Impacts from this research will extend from basic research problems underpinning science-based fisheries management and decision making, to broader societally relevant problems. The project outcomes will most likely guide the development of future commercially available instruments for fisheries and ecosystem assessment for users from both the scientific and fisheries research communities. This project will develop a combined wide-band acoustic scattering and two-scale large-area camera imaging towed instrument, rated to depths as great as 2,000 m, integrated with environmental sensors that can address many of the challenges associated with sampling in the mesopelagic and bathypelagic zones. This instrument capitalizes on emerging broadband acoustical approaches. The acoustic frequencies will span 1-450 kHz almost continuously, simultaneously providing ?full spectrum? information on zooplankton and micronekton, with the lower frequencies optimized for resonance classification of gas-bearing organism, such as myctophids and siphonophores, and the higher frequencies optimized for spectral classification of organism without gas-inclusions, such as euphausiids and salps. The two-scale camera system will provide images of these organisms over a large area for taxa/species-level classification as well as behavioral observation, including imaging larger and mobile micronekton, and will ground-truth the synoptic acoustic data.