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Francis Marsac - One of the best experts on this subject based on the ideXlab platform.
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Seamounts, plateaus and governance issues in the southwestern Indian Ocean, with emphasis on fisheries management and marine conservation, using the Walters Shoal as a case study for implementing a protection framework
Deep Sea Research Part II: Topical Studies in Oceanography, 2020Co-Authors: Francis Marsac, J.-f. Ternon, Florence Galletti, E.v. Romanov, Hervé Demarcq, L. Corbari, P. Bouchet, W.r. Roest, S.j. Jorry, K. OluAbstract:There is a growing interest in the management of Seamounts of the Southwestern Indian Ocean (SWIO) both in waters under national jurisdictions and in the Areas Beyond National Jurisdiction (ABNJ). New scientific knowledge has been gathered through various oceanographic cruises during the past decade, and new agreements are under consideration globally to promote conservation and sustainable use of the biodiversity in the ABNJ, where the deep sea ecosystems associated with Seamounts are a growing matter of concern. SWIO Seamounts have attracted the interests of fishers since the 1960s, and contracts for mining exploration have been granted recently. Seamounts are known to shelter rich, fragile and poorly resilient ecosystems whose important ecological functions are threatened by various anthropogenic pressures. Whereas many Seamounts and shoals are located in national waters, many others fall in the ABNJ, with no current legal status per se. To ensure conservation of their habitats and biodiversity, it is essential that protection measures are instigated under an internationally recognized legal and institutional framework. In this paper, we review the current state of such a framework relevant to Seamounts, with emphasis on fisheries and conservation in the SWIO. An emblematic Seamount, the Walters Shoal, is selected as a case study to discuss how it could become a fully-protected space in the ABNJ. As a large part of the SWIO is under the mandate of the Nairobi Convention (as a Regional Sea under the auspices of UNEP), guidelines are proposed to encourage dedicated Seamount governance within the framework of this Convention
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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.
Telmo Morato - One of the best experts on this subject based on the ideXlab platform.
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A perspective on the importance of oceanic fronts in promoting aggregation of visitors to Seamounts
Fish and Fisheries, 2015Co-Authors: Telmo Morato, Peter I. Miller, Daniel C. Dunn, Simon J. Nicol, James Bowcott, Patrick N. HalpinAbstract:Recent evidence has demonstrated that not all Seamounts are areas where productivity, biomass and biodiversity of marine life thrive. Therefore, understanding the drivers and mechanisms underlying Seamount productivity is a major challenge in today's Seamount research. Incorporating oceanographic data in future analyses has been suggested to be of paramount importance to unveil many of the Seamount ecology paradigms. Persistent hydrographic features, such as oceanic fronts, have been recognized to enhance biological activity and to drive marine animal distributions and migration patterns. However, the importance of oceanic fronts in driving aggregations of visiting animals on Seamounts has not been understood yet. Here, we analysed a data set of Seamounts in the Pacific Ocean alongside satellite-derived maps of strong, persistent and frequently occurring oceanographic features, to evaluate if oceanic fronts promote aggregation of visitors on Seamounts. Our analyses suggest that Seamounts with a higher front frequency were more likely to aggregate tuna catch than average Seamounts. However, it appears that fronts may be driving factors for aggregation only if present above a certain threshold. These results highlight the importance of environmental conditions in general, and oceanic fronts in particular, in promoting Seamount productivity. We therefore argue that a thorough examination of the oceanographic conditions promoting Seamount productivity at various temporal and spatial scales is warranted in future Seamount research agendas.
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A global assessment of Seamount ecosystems knowledge using an ecosystem evaluation framework
Biological Conservation, 2014Co-Authors: Kristina Øie Kvile, Gerald H. Taranto, Tony J. Pitcher, Telmo MoratoAbstract:Abstract Seamounts are ubiquitous habitats of the deep-sea, collectively forming an area as large as Europe. Their characteristics have led marine scientists to hypothesize a series of ‘Seamount effects’ enhancing numbers of endemic species, rates of production and bentho-pelagic trophic transfers. These effects have profound implications for deep-sea management; collating the existing body of Seamount knowledge to describe potential effects on individual Seamounts is therefore of paramount importance. In the course of this study, relevant literature was searched for key geological, oceanographic and ecological Seamount attributes, and assembled in a ‘Google Earth’ map and in an online database (the Seamount Ecosystem Evaluation Framework, SEEF, www.Seamounteef.org ), comprising 597 Seamounts located in the Atlantic, Pacific, Southern and Mediterranean basins. Data collated were described both in terms of quality and quantity, and the status of past and present global Seamount knowledge was assessed. In addition, we investigated to what extent the available information supports Seamount functioning hypotheses. The analysis confirms that Seamounts remain largely unexplored, with only 0.4–4% of the total Seamount population directly sampled for scientific purposes. Some of the Seamount hypotheses tested are better supported than others, for example, some Seamounts may represent ‘oases’ of the abyssal plains and some may play a role in connecting benthic and pelagic communities. However, Seamounts present heterogeneous geophysical settings, suggesting that not all Seamounts affect the food webs and biogeochemical fluxes in the surrounding ocean in the same way. Therefore, SEEF constitutes a tool to identify features playing a key role in deep-sea ecosystems.
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Seamount physiography and biology in the north-east Atlantic and Mediterranean Sea
Biogeosciences, 2013Co-Authors: Telmo Morato, Ricardo S. Santos, Kristina Øie Kvile, Gerald H. Taranto, Fernando Tempera, Bhavani Narayanaswamy, Dierk Hebbeln, Gui M. Menezes, Claudia Wienberg, Tony J. PitcherAbstract:Abstract. This work aims at characterising the Seamount physiography and biology in the OSPAR Convention limits (north-east Atlantic Ocean) and Mediterranean Sea. We first inferred potential abundance, location and morphological characteristics of Seamounts, and secondly, summarized the existing biological, geological and oceanographic in situ research, identifying examples of well-studied Seamounts. Our study showed that the Seamount population in the OSPAR area (north-east Atlantic) and in the Mediterranean Sea is large with around 557 and 101 Seamount-like features, respectively. Similarly, Seamounts occupy large areas of about 616 000 km2 in the OSPAR region and of about 89 500 km2 in the Mediterranean Sea. The presence of Seamounts in the north-east Atlantic has been known since the late 19th century, but overall knowledge regarding Seamount ecology and geology is still relatively poor. Only 37 Seamounts in the OSPAR area (3.5% of all Seamounts in the region), 22 in the Mediterranean Sea (9.2% of all Seamounts in the region) and 25 in the north-east Atlantic south of the OSPAR area have in situ information. Seamounts mapped in both areas are in general very heterogeneous, showing diverse geophysical characteristics. These differences will likely affect the biological diversity and production of resident and associated organisms.
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an ecosystem evaluation framework for global Seamount conservation and management
PLOS ONE, 2012Co-Authors: Gerald H. Taranto, Kristina Øie Kvile, Tony J. Pitcher, Telmo MoratoAbstract:In the last twenty years, several global targets for protection of marine biodiversity have been adopted but have failed. The Convention on Biological Diversity (CBD) aims at preserving 10% of all the marine biomes by 2020. For achieving this goal, ecologically or biologically significant areas (EBSA) have to be identified in all biogeographic regions. However, the methodologies for identifying the best suitable areas are still to be agreed. Here, we propose a framework for applying the CBD criteria to locate potential ecologically or biologically significant Seamount areas based on the best information currently available. The framework combines the likelihood of a Seamount constituting an EBSA and its level of human impact and can be used at global, regional and local scales. This methodology allows the classification of individual Seamounts into four major portfolio conservation categories which can help optimize management efforts toward the protection of the most suitable areas. The framework was tested against 1000 dummy Seamounts and satisfactorily assigned Seamounts to proper EBSA and threats categories. Additionally, the framework was applied to eight case study Seamounts that were included in three out of four portfolio categories: areas highly likely to be identified as EBSA with high degree of threat; areas highly likely to be EBSA with low degree of threat; and areas with a low likelihood of being EBSA with high degree of threat. This framework will allow managers to identify Seamount EBSAs and to prioritize their policies in terms of protecting undisturbed areas, disturbed areas for recovery of habitats and species, or both based on their management objectives. It also identifies Seamount EBSAs and threats considering different ecological groups in both pelagic and benthic communities. Therefore, this framework may represent an important tool to mitigate Seamount biodiversity loss and to achieve the 2020 CBD goals.
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mapping condor Seamount seafloor environment and associated biological assemblages azores ne atlantic
Seafloor Geomorphology as Benthic Habitat#R##N#GeoHAB Atlas of Seafloor Geomorphic Features and Benthic Habitats, 2012Co-Authors: Fernando Tempera, Igor Bashmachnikov, Ana Mendonça, Ana M. Martins, Telmo Morato, Neil C. Mitchell, Eva Giacomello, Aldino S Campos, Andreia Braga Henriques, Ana ColacoAbstract:Publisher Summary Seamounts are among the most common topographic features in the world ocean. Depending on their particular morphological traits, they can also be referred to as banks, knolls, guyots, mounds, or hills. Condor Seamount is a linear volcano located in the Azores (northeast Atlantic), 35 km in length, 2–6 km wide, and of varied seafloor morphology. A scientific observatory devoted to research on Seamount ecosystem structure and functioning has been established on Condor, secured by a temporary fishing closure. Multiple projects have contributed to this observatory by targeting the Seamount with snapshots and long-term deployments of moored, satellite-based, and shipborne technologies. This chapter presents a brief characterization of the Seamount's seafloor environment by focusing on the multibeam bathymetry data and a series of video, oceanographic, and fishery surveys. A classification based upon the bathymetric position index is presented to characterize the landscape composition of the Seamount. Habitats of conservation importance, such as coral gardens and deep-sea sponge aggregations, are documented. A qualitative zonation of the benthic assemblages based on the video surveys is presented along with dominant fish and crustacean catch data for comparable depth strata. Understanding how deep-sea habitat-building species like corals and sponges distribute at fine scales over the complex topography of individual Seamounts is therefore critical information to design usage zonation schemes.
J.-f. Ternon - One of the best experts on this subject based on the ideXlab platform.
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Seamounts, plateaus and governance issues in the southwestern Indian Ocean, with emphasis on fisheries management and marine conservation, using the Walters Shoal as a case study for implementing a protection framework
Deep Sea Research Part II: Topical Studies in Oceanography, 2020Co-Authors: Francis Marsac, J.-f. Ternon, Florence Galletti, E.v. Romanov, Hervé Demarcq, L. Corbari, P. Bouchet, W.r. Roest, S.j. Jorry, K. OluAbstract:There is a growing interest in the management of Seamounts of the Southwestern Indian Ocean (SWIO) both in waters under national jurisdictions and in the Areas Beyond National Jurisdiction (ABNJ). New scientific knowledge has been gathered through various oceanographic cruises during the past decade, and new agreements are under consideration globally to promote conservation and sustainable use of the biodiversity in the ABNJ, where the deep sea ecosystems associated with Seamounts are a growing matter of concern. SWIO Seamounts have attracted the interests of fishers since the 1960s, and contracts for mining exploration have been granted recently. Seamounts are known to shelter rich, fragile and poorly resilient ecosystems whose important ecological functions are threatened by various anthropogenic pressures. Whereas many Seamounts and shoals are located in national waters, many others fall in the ABNJ, with no current legal status per se. To ensure conservation of their habitats and biodiversity, it is essential that protection measures are instigated under an internationally recognized legal and institutional framework. In this paper, we review the current state of such a framework relevant to Seamounts, with emphasis on fisheries and conservation in the SWIO. An emblematic Seamount, the Walters Shoal, is selected as a case study to discuss how it could become a fully-protected space in the ABNJ. As a large part of the SWIO is under the mandate of the Nairobi Convention (as a Regional Sea under the auspices of UNEP), guidelines are proposed to encourage dedicated Seamount governance within the framework of this Convention
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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.
Pavanee Annasawmy - 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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Structures des communautés micronectoniques en relation avec les conditions environnementales à deux monts sous-marins peu profonds du sud-ouest de l'Océan Indien
2019Co-Authors: Pavanee AnnasawmyAbstract:Seamounts are ubiquitous topographic features across all ocean basins. They rise steeply through the water column from abyssal depths. Depending on their size, shape and summit depths, Seamounts reportedly have an impact on the physical flow regimes which may promote the aggregation of zooplankton, micronekton, and top predators above or in the immediate vicinity of their summits. Micronekton form a key trophic link between zooplankton and top marine predators and are divided into four broad categories: gelatinous plankton, crustaceans, cephalopods and mesopelagic fishes. The vertical and horizontal distributions, assemblages and trophic relationships of micronekton were investigated at two shallow Seamounts of the south-western Indian Ocean. La Pérouse Seamount is a steep bathymetric feature rising from a deep seabed located at 5000 m and with a summit depth at ~ 60 m below the sea surface. The Seamount is located at the north-western periphery of the oligotrophic Indian South Subtropical Gyre province. MAD-Ridge Seamount (“thus called in this study”), is ~ 240 m below the sea surface rising from a base located at ~2400 m. The Seamount is located within an “eddy corridor” to the south of Madagascar within the productive East African Coastal Province. Chapter 4 investigates the influence of mesoscale eddies, Madagascar shelf and shallow Seamounts on the distribution of micronekton using an acoustic approach. It is demonstrated that mesoscale eddies and the continental shelf may show enhanced acoustic densities of micronekton compared to MAD-Ridge Seamount. The micronekton acoustic densities were also greater at MAD-Ridge compared to La Pérouse, in accordance with the difference in productivity between the two sites. Chapter 5 is dedicated to the micronekton assemblages and diel migration patterns of micronekton communities. It is shown that, while the shallow scattering layer (0-200 m) consisted of oceanic micronekton species; the summits and flanks of La Pérouse and MAD-Ridge showed presence of resident or Seamount-associated species both during the day and night. I also discussed the different migration strategies of micronekton. Chapter 6 investigates the stable isotope patterns of mesopelagic communities at La Pérouse and MAD-Ridge. Despite the differing productivity at La Pérouse and MAD-Ridge, gelatinous organisms, crustaceans, smaller-sized squids and mesopelagic fishes exhibited trophic levels ranging from 2 to 4 at both Seamounts. This thesis highlights important knowledge gaps on Seamount ecosystems and ecological patterns associated to shallow Seamounts. It also underlines the importance of studying Seamount ecosystems of the south-western Indian Ocean in order to promote management and conservation measures for a sustainable use of such specific environments.
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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.
Tony J. Pitcher - One of the best experts on this subject based on the ideXlab platform.
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A global assessment of Seamount ecosystems knowledge using an ecosystem evaluation framework
Biological Conservation, 2014Co-Authors: Kristina Øie Kvile, Gerald H. Taranto, Tony J. Pitcher, Telmo MoratoAbstract:Abstract Seamounts are ubiquitous habitats of the deep-sea, collectively forming an area as large as Europe. Their characteristics have led marine scientists to hypothesize a series of ‘Seamount effects’ enhancing numbers of endemic species, rates of production and bentho-pelagic trophic transfers. These effects have profound implications for deep-sea management; collating the existing body of Seamount knowledge to describe potential effects on individual Seamounts is therefore of paramount importance. In the course of this study, relevant literature was searched for key geological, oceanographic and ecological Seamount attributes, and assembled in a ‘Google Earth’ map and in an online database (the Seamount Ecosystem Evaluation Framework, SEEF, www.Seamounteef.org ), comprising 597 Seamounts located in the Atlantic, Pacific, Southern and Mediterranean basins. Data collated were described both in terms of quality and quantity, and the status of past and present global Seamount knowledge was assessed. In addition, we investigated to what extent the available information supports Seamount functioning hypotheses. The analysis confirms that Seamounts remain largely unexplored, with only 0.4–4% of the total Seamount population directly sampled for scientific purposes. Some of the Seamount hypotheses tested are better supported than others, for example, some Seamounts may represent ‘oases’ of the abyssal plains and some may play a role in connecting benthic and pelagic communities. However, Seamounts present heterogeneous geophysical settings, suggesting that not all Seamounts affect the food webs and biogeochemical fluxes in the surrounding ocean in the same way. Therefore, SEEF constitutes a tool to identify features playing a key role in deep-sea ecosystems.
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Seamount physiography and biology in the north-east Atlantic and Mediterranean Sea
Biogeosciences, 2013Co-Authors: Telmo Morato, Ricardo S. Santos, Kristina Øie Kvile, Gerald H. Taranto, Fernando Tempera, Bhavani Narayanaswamy, Dierk Hebbeln, Gui M. Menezes, Claudia Wienberg, Tony J. PitcherAbstract:Abstract. This work aims at characterising the Seamount physiography and biology in the OSPAR Convention limits (north-east Atlantic Ocean) and Mediterranean Sea. We first inferred potential abundance, location and morphological characteristics of Seamounts, and secondly, summarized the existing biological, geological and oceanographic in situ research, identifying examples of well-studied Seamounts. Our study showed that the Seamount population in the OSPAR area (north-east Atlantic) and in the Mediterranean Sea is large with around 557 and 101 Seamount-like features, respectively. Similarly, Seamounts occupy large areas of about 616 000 km2 in the OSPAR region and of about 89 500 km2 in the Mediterranean Sea. The presence of Seamounts in the north-east Atlantic has been known since the late 19th century, but overall knowledge regarding Seamount ecology and geology is still relatively poor. Only 37 Seamounts in the OSPAR area (3.5% of all Seamounts in the region), 22 in the Mediterranean Sea (9.2% of all Seamounts in the region) and 25 in the north-east Atlantic south of the OSPAR area have in situ information. Seamounts mapped in both areas are in general very heterogeneous, showing diverse geophysical characteristics. These differences will likely affect the biological diversity and production of resident and associated organisms.
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an ecosystem evaluation framework for global Seamount conservation and management
PLOS ONE, 2012Co-Authors: Gerald H. Taranto, Kristina Øie Kvile, Tony J. Pitcher, Telmo MoratoAbstract:In the last twenty years, several global targets for protection of marine biodiversity have been adopted but have failed. The Convention on Biological Diversity (CBD) aims at preserving 10% of all the marine biomes by 2020. For achieving this goal, ecologically or biologically significant areas (EBSA) have to be identified in all biogeographic regions. However, the methodologies for identifying the best suitable areas are still to be agreed. Here, we propose a framework for applying the CBD criteria to locate potential ecologically or biologically significant Seamount areas based on the best information currently available. The framework combines the likelihood of a Seamount constituting an EBSA and its level of human impact and can be used at global, regional and local scales. This methodology allows the classification of individual Seamounts into four major portfolio conservation categories which can help optimize management efforts toward the protection of the most suitable areas. The framework was tested against 1000 dummy Seamounts and satisfactorily assigned Seamounts to proper EBSA and threats categories. Additionally, the framework was applied to eight case study Seamounts that were included in three out of four portfolio categories: areas highly likely to be identified as EBSA with high degree of threat; areas highly likely to be EBSA with low degree of threat; and areas with a low likelihood of being EBSA with high degree of threat. This framework will allow managers to identify Seamount EBSAs and to prioritize their policies in terms of protecting undisturbed areas, disturbed areas for recovery of habitats and species, or both based on their management objectives. It also identifies Seamount EBSAs and threats considering different ecological groups in both pelagic and benthic communities. Therefore, this framework may represent an important tool to mitigate Seamount biodiversity loss and to achieve the 2020 CBD goals.
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Abundance and distribution of Seamounts in the Azores
Marine Ecology Progress Series, 2008Co-Authors: Telmo Morato, Tony J. Pitcher, Fernando Tempera, Gui M. Menezes, Miguel Machete, Adrian Kitchingman, Sherman Lai, Ricardo S. SantosAbstract:We characterized the Seamount distribution of the economic exclusive zone (EEZ) of the Azores (Portugal) using 2 bathymetry datasets. Our algorithm showed that peaks and Seamounts are common features in this region of the North Atlantic. The density obtained of 3.3 peaks of all sizes per 1000 km 2 is in the same order of magnitude as that obtained on the Mid-Atlantic Ridge by a few other studies. A total of 63 large and 398 small Seamount-like features are mapped and described in the Azorean EEZ. Our distribution of Seamounts predicts that about 57% of the potential Azores Seamounts lie in the zone protected from deep-water trawling by European Commission Council Regulation No. 1568/2005.
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Evidence of a Seamount effect on aggregating visitors
Marine Ecology Progress Series, 2008Co-Authors: Telmo Morato, Ricardo S. Santos, Miguel Machete, Divya A. Varkey, Carla Damaso, Marco Santos, Rui Prieto, Tony J. PitcherAbstract:It has been suggested that Seamounts hold higher abundances of some 'visiting' ani- mals, such as tuna, sharks, billfishes, marine mammals, sea-turtles and even seabirds, but this has been based on sparse records, and warrants further examination. In this paper we use data from a fishery observer program to examine whether the predicted higher abundances of tuna, marine mammals, sea turtles and seabirds actually occur around Azores Seamounts and to map the distribu- tion of the various species. Our results indicate that some marine predators (skipjack Katsuwonus pelamis and bigeye tuna Thunnus obesus, common dolphin Delphinus delphis and Cory's shearwater Calonectris diomedea borealis) were significantly more abundant in the vicinity of some shallow- water Seamount summits. Our methodology, however, failed to demonstrate a Seamount association for bottlenose dolphins Tursiops truncatus, spotted dolphin Stenella frontalis, sperm whale Physeter macrocephalus, terns Sterna hirundo and S. dougalli, yellow-legged gull Larus cachinnans atlantis and loggerhead sea turtles Caretta caretta. Seamounts may act as feeding stations for some of these visitors. Not all Seamounts, however, seemed to be equally important for these associations. Only Seamounts shallower than 400 m depth showed significant aggregation effects. These Seamounts may be considered hotspots of marine life in the Azores, and a special effort should be made in order to ensure a sustainable management of these habitats.
