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Barbara A Block - One of the best experts on this subject based on the ideXlab platform.
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life in the open ocean seasonal migration and diel diving behaviour of southern hemisphere porbeagle sharks lamna nasus
Marine Biology, 2015Co-Authors: Malcolm P. Francis, John C Holdsworth, Barbara A BlockAbstract:A wide range of pelagic predators survive in the open ocean, yet little is known about how they use that environment. Much of the current information on these species comes from studies in shelf waters, and it is not clear how representative the results are of their oceanic lifestyle. We used pop-up satellite tags to explore the horizontal and vertical use of the open ocean by porbeagle sharks (Lamna nasus) in the south-west Pacific Ocean and to identify possible mitigation measures to reduce their bycatch in tuna longline fisheries. Ten porbeagle sharks were tracked in waters around New Zealand for 72–300 days (median 221 days). Sharks made horizontal movements of hundreds to thousands of kilometres, with a maximum estimated track length of almost 10,000 km. Mature females made seasonal latitudinal migrations from ~46–48°S in summer to ~35–38°S during winter–spring, where they are hypothesised to give birth to pups. Porbeagle sharks exhibited diel vertical migration, diving Deeper during the day than at night. Dives generally began at dawn and finished at dusk and lasted 11–15 h depending on day length. Porbeagles feed mainly on mesopelagic fish and squid and appear to forage in the vertically migrating Deep Scattering Layer. All sharks dived to at least 600 m with a maximum recorded depth of 1024 m. During the day, most of their time was spent at depths of 200–600 m in the open ocean. Porbeagle shark bycatch could be substantially reduced by limiting longline fishing to daylight hours when they are too Deep to be caught. However, longliners currently set mainly at night to avoid seabird bycatch, which would increase unless other mitigation measures were implemented to protect them. A review of factors affecting the bycatch of various species, and the impact of mitigation measures on catches of target species, is required to identify an appropriate suite of management measures.
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vertical movements and habitat utilization of skipjack katsuwonus pelamis yellowfin thunnus albacares and bigeye thunnus obesus tunas in the equatorial eastern pacific ocean ascertained through archival tag data
2009Co-Authors: Kurt M Schaefer, Daniel W Fuller, Barbara A BlockAbstract:Skipjack, yellowfin, and bigeye tunas were caught and released with implanted archival tags in the equatorial eastern Pacific Ocean between 2004 and 2006. The depth and temperature data from five recovered archival tags for each species were analyzed and compared among species while at liberty within the same geographically defined area. Evaluations of the timed depth records resulted in discrimination of distinct vertical movement patterns for each species, including association with floating objects, daytime foraging below the thermocline in depths of the Deep Scattering Layer, surface orientation, and Deep diving in excess of 500 m. During the daytime, skipjack and yellowfin tunas occasionally exhibited repetitive bounce-dive foraging behavior well below the thermocline to depths of the Deep Scattering Layer, between 225 and 400 m. Bigeye tuna were foraging during the daytime at similar depths of about 225–475 m, except when undertaking upward forays. The Deepest dives recorded for skipjack, yellowfin, and bigeye tunas were 596, 1022, and 1695 m, respectively. The vertical habitat utilization distributions indicate that skipjack, yellowfin, and bigeye tunas, when not associated with floating objects, spent 99, 96, and 92%, respectively, of their time above the thermocline during the night, but spent 37, 44, and 57%, respectively, of their time below the thermocline during the day. The apparent species-specific physiological abilities and tolerances to environmental characteristics of their vertical habitat, including dissolved oxygen and temperature, are evaluated. Results of this study on the comparative vertical movements, behavior, and habitat utilization for these species, should also be useful in evaluations of species-specific vulnerability to purse-seine and longline fisheries in this region.
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movements behavior and habitat utilization of yellowfin tuna thunnus albacares in the northeastern pacific ocean ascertained through archival tag data
Marine Biology, 2007Co-Authors: Kurt M Schaefer, Daniel W Fuller, Barbara A BlockAbstract:Sixty-eight yellowfin tuna, Thunnus albacares, (60-135 cm fork length) were caught and released with implanted archival tags offshore off Baja California, Mexico, during October 2002 and October 2003. Thirty-six fish (53%) were recaptured and the data were downloaded from all 36 recovered tags. Time at liberty ranged from 9 to 1,161 days, and the data were analyzed for the 20 fish that were at liberty for 154 or more days. The accuracy in the position estimates, derived from light-level longitude data and sea-surface temperatures (SSTs) based latitude, is about 0.41° in longitude and 0.82° in latitude, in this region. The movement paths, derived from position estimates, for the 20 yellowfin indicated that 19 (95%) remained within 1,445 km of their release locations. The estimated mean velocity along movement paths was 77 km/day. The southern and northern seasonal movement paths observed for yellowfin off Baja California are influenced by the seasonal movements of the 18°C SST isotherm. Cyclical movements to and from suitable spawning habitat (≥24°C SST) was observed only for mature fish. For the 12 fish that demonstrated site fidelity, the mean 95 and 50% utilization distributions were 258,730 km2 and 41,260 km2, respectively. Evaluations of the timed depth records resulted in discrimination of four distinct behaviors. When exhibiting type-1 diving behavior (78.1% of all days at liberty) the fish remained at depths less than 50 m at night and did not dive to depths greater than about 100 m during the day. Type-2 diving behavior (21.2% of all days at liberty) was characterized by ten or more dives in excess of 150 m during the day. Type-2 diving behavior is apparently a foraging strategy for fish targeting prey organisms of the Deep-Scattering Layer during the day, following nighttime foraging within the mixed Layer on the same prey. Yellowfin tuna exhibited occasional Deep-diving behavior, and some dives exceeded 1,000 m, where ambient temperatures were less than 5°C. Surface-oriented behavior, defined as the time fish remained at depths less than 10 m for more than 10 min, were evaluated. The mean number and duration of surface-oriented events per day for all fish was 14.3 and 28.5 min, respectively. Habitat utilization of yellowfin, presented as monthly composite horizontal and vertical distributions, indicates confined geographical distributions, apparently resulting from an affinity to an area of high prey availability. The vertical distributions indicate greater daytime depths in relation to a seasonally Deeper mixed Layer and a greater proportion of daytime at shallower depths in relation to a seasonally shallower mixed Layer.
Richard E Thomson - One of the best experts on this subject based on the ideXlab platform.
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distribution of zooplankton associated with the endeavour ridge hydrothermal plume
Journal of Plankton Research, 1995Co-Authors: Brenda J Burd, Richard E ThomsonAbstract:Enhanced zooplankton biomass was found in shallow ( 900 m) net samples collected over the Endeavour Ridge hydrothermal plume in 1991 and 1992. This enhanced biomass was manifest in considerably higher abundance values for most species in proximity to the vent field compared with abundance values from net samples collected 10-50 km off-axis. The species most enriched in abundance by the hydrothermal plume were those normally found in the mid-depth Scattering Layer at 400- 900 m depth. These mid-depth animals were also the dominant fauna in the Deep Scattering Layers that overlie the hydrothermal plume at depths of 1200-1900 m near the main vent field. The abundance and biomass dominants were species with pronounced ontogenetic migration patterns, and their associated predators. The abundance of many typically Deep species was also enhanced over the main vent field. Faunal compositions of net samples were compared using a similarity measure and average linkage rule. Deep fauna in proximity to the vent field but not associated with Scattering Layers (Group 1), were similar to Deep fauna 10-50 km off- axis. The fauna of the Deep Scattering Layer over the vent field (Group 2) was most similaT to surface and mid- depth Scattering Layer fauna found within a 50 km radius of the vent field. Statistical tests of linkages obtained using a bootstrap method indicate that the abundance and taxonomic composition of the two faunal groups were significantly distinct in 1992, but not in 1991. We conclude that there was considerable infiltration of shallow fauna into the Deep Scattering Layers within 2-3 km of the main vent field, less extensive infiltration 10-15 km to the north and south of the vent field in 1991, and insignificant infiltration at stations 50 km to the west of the vent field in 1992. A bootstrap analysis comparing the faunal composition of nets towed above 900 m depth showed that shallow fauna were not significantly distinct between the two sampling years or up to 50 km away from the vent field.
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composition of a Deep Scattering Layer overlying a mid ocean ridge hydrothermal plume
Marine Biology, 1992Co-Authors: Brenda J Burd, Richard E Thomson, Glen S JamiesonAbstract:Three sets of zooplankton trawls with multiple nets were deployed in June 1990 within a Deep (2000 m) Scattering Layer overlying the central hydrothermal vent field on the Endeavour segment of Juan de Fuca Ridge in the northeast Pacific. Trawl data were collected concurrently with temperature, salinity, light attenuation and acoustic (150 kHz) backscatter profiles. We describe the composition, size distribution and biomass of zooplankton collected in the net samples, and compare biomass distributions with physical characteristics of the hydrothermal plume. The nine discrete trawl samples (1 mm mesh) contained zooplankton biomass of between 0.3 and 21 mg dry wt m-3 with the highest biomass samples coincident with large and positive (+20 dB) acoustic backscatter anomalies observed above the top of the hydrothermal plume. Lowest biomass samples were coincident with small, negative (-5 dB) backscatter anomalies within the core of the plume. Results suggest that the region within a hundred meters of the top of the plume was a zone of enhanced zooplankton concentration associated with nutrition enrichment related to the plume. In contrast, the plume core was a zone of faunal depletion, presumably linked to adverse plume chemistry. The species composition and size distribution profiles from net samples revealed that the epi-plume assemblage contained several trophic levels of bathypelagic fauna, but did not contain benthic larvae or vent-related benthopelagic fauna.
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the Deep Scattering Layer associated with the endeavour ridge hydrothermal plume
Deep Sea Research Part A. Oceanographic Research Papers, 1992Co-Authors: Richard E Thomson, Brenda J Burd, Lee R Gordon, Adrian G Dolling, Glen S JamiesonAbstract:Abstract We analyse surface-to-bottom profiles of temperature, salinity, light attenuation coefficient and acoustic (150 kHz) backscatter intensity collected in June 1990 in the vicinity of the central hydrothermal vent field on Endeavour Ridge in the northeast Pacific. Data from coincident Deep plankton net tows corroborate earlier speculation (Thomson et al., 1991, Journal of Geophysical Research, 96, 4839-4844) that the 100 m thick acoustic Scattering Layer found near 1.9 km depth in this region consists of a dense concentration of macrozooplankton living near the top of the plume-contaminated bottom waters. Peak (≈10 dB) acoustic anomalies in the June 1990 backscatter Layer were located near the top of the plume at depths of 1800–2000 m throughout the principal 60 km2 study area. The Scattering Layer contained a high Zooplankton biomass of 21 mg m−3 and maximum species richness of 83 taxa. In all profiles, the backscatter intensity decreased to anomalously low values beneath the core of the plume. The presence of the backscatter Layer 12 km to the east of the vent site is evidence for Zooplankton Layering beyond the immediate confines of the ridge. We conclude that pelagic and Deep-sea Zooplankton congregate near the top of the plumecontaminated bottom waters in the vicinity of the ridge to take advantage of increased concentrations of chemosynthetic bacteria, fine-grained particles and other nutrients carried vertically upward by the buoyant portions of the plume. The Zooplankton depletion below the central core of the spreading hydrothermal plume indicates that Zooplankton avoid elevated concentrations of hydrothermally-derived minerals and other chemicals inherent to the main body of the plume.
Francis Marsac - One of the best experts on this subject based on the ideXlab platform.
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Micronekton distributions and assemblages at two shallow seamounts of the south-western Indian Ocean: Insights from acoustics and mesopelagic trawl data
Progress in Oceanography, 2019Co-Authors: Pavanee Annasawmy, Anne Lebourges-dhaussy, J.-f. Ternon, Yves Cherel, Gildas Roudaut, Frédéric Ménard, Pascal Cotel, Evgeny Romanov, Francis MarsacAbstract:Micronekton distributions and assemblages were investigated at two shallow seamounts of the south-western Indian Ocean using a combination of trawl data and multi-frequency acoustic visualisation techniques. La Pérouse (∼60 m) seamount is located on the outskirts of the oligotrophic Indian South Subtropical Gyre province with weak mesoscale activities and low primary productivity all year round. The “MAD-Ridge” seamount (thus termed in this study; ∼240 m) is located in the productive East African Coastal (EAFR) province with high mesoscale activities to the south of Madagascar. This resulted in higher micronekton species richness at MAD-Ridge compared to La Pérouse. Resulting productivity at MAD-Ridge seamount was likely due to the action of mesoscale eddies advecting larvae and productivity from the Madagascar shelf rather than local dynamic processes such as Taylor column formation. Mean micronekton abundance/biomass, as estimated from mesopelagic trawl catches, were lower over the summit compared to the vicinity of the seamounts, due to net selectivity and catchability and depth gradient on micronekton assemblages. Mean acoustic densities in the night shallow Scattering Layer (SSL: 10-200 m) over the summit were not significantly different compared to the vicinity (within 14 nautical miles) of MAD-Ridge. At La Pérouse and MAD-Ridge, the night and day SSL were dominated by common diel vertical migrant and non-migrant micronekton species respectively. While seamount-associated mesopelagic fishes such as Diaphus suborbitalis (La Pérouse and MAD-Ridge) and Benthosema fibulatum performed diel vertical migrations (DVM) along the seamounts’ flanks, seamount-resident benthopelagic fishes, including Cookeolus japonicus (MAD-Ridge), were aggregated over MAD-Ridge summit both during the day and night. Before sunrise, mid-water migrants initiated the first vertical migration event from the intermediate to the Deep Scattering Layer (DSL, La Pérouse: 500-650m; MAD-Ridge: 400-700 m) or Deeper. During sunrise, the other taxa contributing to the night SSL exhibited a successive series of vertical migration events from the surface to the DSL or Deeper. Some scatterers were blocked in their upward and downward migrations due to the seamount topography, more commonly known as the sound Scattering Layer interception/topographic blockage hypothesis. Possible mechanisms leading to the observed patterns in micronekton vertical and horizontal distributions are discussed. This study contributes to a better understanding of how seamounts influence the diel vertical migration, horizontal distribution and community composition of micronekton and seamount-associated/resident species at two poorly studied shallow topographic features in the south-western Indian Ocean.
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Micronekton distributions and assemblages at two shallow seamounts of the south-western Indian Ocean: Insights from acoustics and mesopelagic trawl data
Progress in Oceanography, 2019Co-Authors: Pavanee Annasawmy, Anne Lebourges-dhaussy, J.-f. Ternon, Yves Cherel, Gildas Roudaut, Frédéric Ménard, Pascal Cotel, Evgeny V. Romanov, Francis MarsacAbstract:Micronekton distributions and assemblages were investigated at two shallow seamounts of the south-western Indian Ocean using a combination of trawl data and multi-frequency acoustic visualisation techniques. La Perouse (∼60 m) seamount is located on the outskirts of the oligotrophic Indian South Subtropical Gyre province with weak mesoscale activities and low primary productivity all year round. The “MAD-Ridge” seamount (thus termed in this study; ∼240 m) is located in the productive East African Coastal (EAFR) province with high mesoscale activities to the south of Madagascar. This resulted in higher micronekton species richness at MAD-Ridge compared to La Perouse. Resulting productivity at MAD-Ridge seamount was likely due to the action of mesoscale eddies advecting larvae and productivity from the Madagascar shelf rather than local dynamic processes such as Taylor column formation. Mean micronekton abundance/biomass, as estimated from mesopelagic trawl catches, were lower over the summit compared to the vicinity of the seamounts, due to net selectivity and catchability and depth gradient on micronekton assemblages. Mean acoustic densities in the night shallow Scattering Layer (SSL: 10-200 m) over the summit were not significantly different compared to the vicinity (within 14 nautical miles) of MAD-Ridge. At La Perouse and MAD-Ridge, the night and day SSL were dominated by common diel vertical migrant and non-migrant micronekton species respectively. While seamount-associated mesopelagic fishes such as Diaphus suborbitalis (La Perouse and MAD-Ridge) and Benthosema fibulatum performed diel vertical migrations (DVM) along the seamounts’ flanks, seamount-resident benthopelagic fishes, including Cookeolus japonicus (MAD-Ridge), were aggregated over MAD-Ridge summit both during the day and night. Before sunrise, mid-water migrants initiated the first vertical migration event from the intermediate to the Deep Scattering Layer (DSL, La Perouse: 500-650m; MAD-Ridge: 400-700 m) or Deeper. During sunrise, the other taxa contributing to the night SSL exhibited a successive series of vertical migration events from the surface to the DSL or Deeper. Some scatterers were blocked in their upward and downward migrations due to the seamount topography, more commonly known as the sound Scattering Layer interception/topographic blockage hypothesis. Possible mechanisms leading to the observed patterns in micronekton vertical and horizontal distributions are discussed. This study contributes to a better understanding of how seamounts influence the diel vertical migration, horizontal distribution and community composition of micronekton and seamount-associated/resident species at two poorly studied shallow topographic features in the south-western Indian Ocean.
Glen S Jamieson - One of the best experts on this subject based on the ideXlab platform.
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composition of a Deep Scattering Layer overlying a mid ocean ridge hydrothermal plume
Marine Biology, 1992Co-Authors: Brenda J Burd, Richard E Thomson, Glen S JamiesonAbstract:Three sets of zooplankton trawls with multiple nets were deployed in June 1990 within a Deep (2000 m) Scattering Layer overlying the central hydrothermal vent field on the Endeavour segment of Juan de Fuca Ridge in the northeast Pacific. Trawl data were collected concurrently with temperature, salinity, light attenuation and acoustic (150 kHz) backscatter profiles. We describe the composition, size distribution and biomass of zooplankton collected in the net samples, and compare biomass distributions with physical characteristics of the hydrothermal plume. The nine discrete trawl samples (1 mm mesh) contained zooplankton biomass of between 0.3 and 21 mg dry wt m-3 with the highest biomass samples coincident with large and positive (+20 dB) acoustic backscatter anomalies observed above the top of the hydrothermal plume. Lowest biomass samples were coincident with small, negative (-5 dB) backscatter anomalies within the core of the plume. Results suggest that the region within a hundred meters of the top of the plume was a zone of enhanced zooplankton concentration associated with nutrition enrichment related to the plume. In contrast, the plume core was a zone of faunal depletion, presumably linked to adverse plume chemistry. The species composition and size distribution profiles from net samples revealed that the epi-plume assemblage contained several trophic levels of bathypelagic fauna, but did not contain benthic larvae or vent-related benthopelagic fauna.
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the Deep Scattering Layer associated with the endeavour ridge hydrothermal plume
Deep Sea Research Part A. Oceanographic Research Papers, 1992Co-Authors: Richard E Thomson, Brenda J Burd, Lee R Gordon, Adrian G Dolling, Glen S JamiesonAbstract:Abstract We analyse surface-to-bottom profiles of temperature, salinity, light attenuation coefficient and acoustic (150 kHz) backscatter intensity collected in June 1990 in the vicinity of the central hydrothermal vent field on Endeavour Ridge in the northeast Pacific. Data from coincident Deep plankton net tows corroborate earlier speculation (Thomson et al., 1991, Journal of Geophysical Research, 96, 4839-4844) that the 100 m thick acoustic Scattering Layer found near 1.9 km depth in this region consists of a dense concentration of macrozooplankton living near the top of the plume-contaminated bottom waters. Peak (≈10 dB) acoustic anomalies in the June 1990 backscatter Layer were located near the top of the plume at depths of 1800–2000 m throughout the principal 60 km2 study area. The Scattering Layer contained a high Zooplankton biomass of 21 mg m−3 and maximum species richness of 83 taxa. In all profiles, the backscatter intensity decreased to anomalously low values beneath the core of the plume. The presence of the backscatter Layer 12 km to the east of the vent site is evidence for Zooplankton Layering beyond the immediate confines of the ridge. We conclude that pelagic and Deep-sea Zooplankton congregate near the top of the plumecontaminated bottom waters in the vicinity of the ridge to take advantage of increased concentrations of chemosynthetic bacteria, fine-grained particles and other nutrients carried vertically upward by the buoyant portions of the plume. The Zooplankton depletion below the central core of the spreading hydrothermal plume indicates that Zooplankton avoid elevated concentrations of hydrothermally-derived minerals and other chemicals inherent to the main body of the plume.
Brenda J Burd - One of the best experts on this subject based on the ideXlab platform.
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distribution of zooplankton associated with the endeavour ridge hydrothermal plume
Journal of Plankton Research, 1995Co-Authors: Brenda J Burd, Richard E ThomsonAbstract:Enhanced zooplankton biomass was found in shallow ( 900 m) net samples collected over the Endeavour Ridge hydrothermal plume in 1991 and 1992. This enhanced biomass was manifest in considerably higher abundance values for most species in proximity to the vent field compared with abundance values from net samples collected 10-50 km off-axis. The species most enriched in abundance by the hydrothermal plume were those normally found in the mid-depth Scattering Layer at 400- 900 m depth. These mid-depth animals were also the dominant fauna in the Deep Scattering Layers that overlie the hydrothermal plume at depths of 1200-1900 m near the main vent field. The abundance and biomass dominants were species with pronounced ontogenetic migration patterns, and their associated predators. The abundance of many typically Deep species was also enhanced over the main vent field. Faunal compositions of net samples were compared using a similarity measure and average linkage rule. Deep fauna in proximity to the vent field but not associated with Scattering Layers (Group 1), were similar to Deep fauna 10-50 km off- axis. The fauna of the Deep Scattering Layer over the vent field (Group 2) was most similaT to surface and mid- depth Scattering Layer fauna found within a 50 km radius of the vent field. Statistical tests of linkages obtained using a bootstrap method indicate that the abundance and taxonomic composition of the two faunal groups were significantly distinct in 1992, but not in 1991. We conclude that there was considerable infiltration of shallow fauna into the Deep Scattering Layers within 2-3 km of the main vent field, less extensive infiltration 10-15 km to the north and south of the vent field in 1991, and insignificant infiltration at stations 50 km to the west of the vent field in 1992. A bootstrap analysis comparing the faunal composition of nets towed above 900 m depth showed that shallow fauna were not significantly distinct between the two sampling years or up to 50 km away from the vent field.
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composition of a Deep Scattering Layer overlying a mid ocean ridge hydrothermal plume
Marine Biology, 1992Co-Authors: Brenda J Burd, Richard E Thomson, Glen S JamiesonAbstract:Three sets of zooplankton trawls with multiple nets were deployed in June 1990 within a Deep (2000 m) Scattering Layer overlying the central hydrothermal vent field on the Endeavour segment of Juan de Fuca Ridge in the northeast Pacific. Trawl data were collected concurrently with temperature, salinity, light attenuation and acoustic (150 kHz) backscatter profiles. We describe the composition, size distribution and biomass of zooplankton collected in the net samples, and compare biomass distributions with physical characteristics of the hydrothermal plume. The nine discrete trawl samples (1 mm mesh) contained zooplankton biomass of between 0.3 and 21 mg dry wt m-3 with the highest biomass samples coincident with large and positive (+20 dB) acoustic backscatter anomalies observed above the top of the hydrothermal plume. Lowest biomass samples were coincident with small, negative (-5 dB) backscatter anomalies within the core of the plume. Results suggest that the region within a hundred meters of the top of the plume was a zone of enhanced zooplankton concentration associated with nutrition enrichment related to the plume. In contrast, the plume core was a zone of faunal depletion, presumably linked to adverse plume chemistry. The species composition and size distribution profiles from net samples revealed that the epi-plume assemblage contained several trophic levels of bathypelagic fauna, but did not contain benthic larvae or vent-related benthopelagic fauna.
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the Deep Scattering Layer associated with the endeavour ridge hydrothermal plume
Deep Sea Research Part A. Oceanographic Research Papers, 1992Co-Authors: Richard E Thomson, Brenda J Burd, Lee R Gordon, Adrian G Dolling, Glen S JamiesonAbstract:Abstract We analyse surface-to-bottom profiles of temperature, salinity, light attenuation coefficient and acoustic (150 kHz) backscatter intensity collected in June 1990 in the vicinity of the central hydrothermal vent field on Endeavour Ridge in the northeast Pacific. Data from coincident Deep plankton net tows corroborate earlier speculation (Thomson et al., 1991, Journal of Geophysical Research, 96, 4839-4844) that the 100 m thick acoustic Scattering Layer found near 1.9 km depth in this region consists of a dense concentration of macrozooplankton living near the top of the plume-contaminated bottom waters. Peak (≈10 dB) acoustic anomalies in the June 1990 backscatter Layer were located near the top of the plume at depths of 1800–2000 m throughout the principal 60 km2 study area. The Scattering Layer contained a high Zooplankton biomass of 21 mg m−3 and maximum species richness of 83 taxa. In all profiles, the backscatter intensity decreased to anomalously low values beneath the core of the plume. The presence of the backscatter Layer 12 km to the east of the vent site is evidence for Zooplankton Layering beyond the immediate confines of the ridge. We conclude that pelagic and Deep-sea Zooplankton congregate near the top of the plumecontaminated bottom waters in the vicinity of the ridge to take advantage of increased concentrations of chemosynthetic bacteria, fine-grained particles and other nutrients carried vertically upward by the buoyant portions of the plume. The Zooplankton depletion below the central core of the spreading hydrothermal plume indicates that Zooplankton avoid elevated concentrations of hydrothermally-derived minerals and other chemicals inherent to the main body of the plume.
