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Auteur Sequeira, A.M.M.; Mellin, C.; Floch, L.; Williams, P.G.; Bradshaw, C.J.A.
Titre Inter-ocean asynchrony in whale shark occurrence patterns Type Article scientifique
Année 2014 Publication Revue Abrégée Journal of Experimental Marine Biology and Ecology
Volume 450 Numéro Pages 21-29
Mots-Clés <!–; –><keyword; Handled; id=; Not; Tag
Résumé (up) Abstract The whale shark (Rhincodon typus, Smith, 1828) is a migratory species (classed as Vulnerable by the IUCN) with genetic and circumstantial evidence for inter-ocean connectivity. Given this migratory behaviour, population-wide occurrence trends can only be contextualized by examining the synchrony in occurrence patterns among locations where they occur. We present a two-step modelling approach of whale shark spatial and temporal probability of occurrence in the Atlantic and Pacific Oceans using generalized linear mixed-effects models. To test the hypothesis that the probability of whale shark occurrence is asynchronous across oceans, as expected if inter-ocean migration occurs, we used long-term datasets of whale shark sightings derived from tuna purse-seine logbooks covering most of the central-east Atlantic (1980–2010) and western Pacific (2000–2010). We predicted seasonal habitat suitability to produce maps in each area, and then evaluated the relative effect of time (year) on the probability of occurrence to test whether it changed over the study period. We also applied fast Fourier transforms to determine if any periodicity was apparent in whale shark occurrences in each ocean. After partialling out the effects of seasonal patterns in spatial distribution and sampling effort, we found no evidence for a temporal trend in whale shark occurrence in the Atlantic, but there was a weak trend of increasing probability of occurrence in the Pacific. The highest-ranked model for the latter included a spatial predictor of occurrence along with fishing effort, a linear term for time, and a random temporal effect (year), explaining 15% of deviance in whale shark probability of occurrence. Fast Fourier transforms revealed a prominent 15.5-year cycle in the Atlantic. The increase in the probability of occurrence in the Pacific is concurrent with a decrease previously detected in the Indian Ocean. Cyclic patterns driven by migratory behaviour would better explain temporal trends in whale shark occurrence at the oceanic scale. However, despite cycles partially explaining observations of fewer sharks in some years, overall reported sighting rate has been decreasing. As a result, we suggest that the current {IUCN} status of the species should be re-assessed, but more data are needed to examine the flow of individuals across oceans and to identify possible reasons for asynchronous occurrences.
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ISSN 0022-0981 ISBN Médium
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Auteur Moreau, S.; Mostajir, B.; Almandoz, G.O.; Demers, S.; Hernando, M.; Lemarchand, K.; Lionard, M.; Mercier, B.; Roy, S.; Schloss, I.R.; Thyssen, M.; Ferreyra, G.A.
Titre Effects of enhanced temperature and ultraviolet B radiation on a natural plankton community of the Beagle Channel (southern Argentina): a mesocosm study Type Article scientifique
Année 2014 Publication Revue Abrégée Aquatic Microbial Ecology
Volume 72 Numéro 2 Pages 155-173
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Résumé (up) ABSTRACT: Marine planktonic communities can be affected by increased temperatures associated with global climate change, as well as by increased ultraviolet B radiation (UVBR, 280-320 nm) through stratospheric ozone layer thinning. We studied individual and combined effects of increased temperature and UVBR on the plankton community of the Beagle Channel, southern Patagonia, Argentina. Eight 2 m3 mesocosms were exposed to 4 treatments (with 2 replicates) during 10 d: (1) control (natural temperature and UVBR), (2) increased UVBR (simulating a 60% decrease in stratospheric ozone layer thickness), (3) increased temperature (+ 3°C), and (4) simultaneous increased temperature and UVBR (60% decrease in stratospheric ozone; + 3°C). Two distinct situations were observed with regard to phytoplankton biomass: bloom (Days 1-4) and post-bloom (Days 5-9). Significant decreases in micro-sized diatoms (>20 µm), bacteria, chlorophyll a, and particulate organic carbon concentrations were observed during the post-bloom in the enhanced temperature treatments relative to natural temperature, accompanied by significant increases in nanophytoplankton (10-20 µm, mainly prymnesiophytes). The decrease in micro-sized diatoms in the high temperature treatment may have been caused by a physiological effect of warming, although we do not have activity measurements to support this hypothesis. Prymnesiophytes benefited from micro-sized diatom reduction in their competition for resources. The bacterial decrease under warming may have been due to a change in the dissolved organic matter release caused by the observed change in phytoplankton composition. Overall, the rise in temperature affected the structure and total biomass of the communities, while no major effect of UVBR was observed on the plankton community.
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 555
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Auteur Levin, N.; Coll, M.; Fraschetti, S.; Gal, G.; Giakoumi, S.; Gke, C.; Heymans, J.J.; Katsanevakis, S.; Mazor, T.; ztrk, B.; Rilov, G.; Gajewski, J.; Steenbeek, J.; Kark, S.
Titre REVIEW Biodiversity data requirements for systematic conservation planning in the Mediterranean Sea Type Article scientifique
Année 2014 Publication Revue Abrégée Mar Ecol Prog Ser
Volume 508 Numéro Pages 261-281
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Résumé (up) ABSTRACT: The Mediterranean Sea’s biodiversity and ecosystems face many threats due to anthropogenic pressures. Some of these include human population growth, coastal urbanization, accelerated human activities, and climate change. To enhance the formation of a science-based system of marine protected areas in the Mediterranean Sea, data on the spatial distribution of ecological features (abiotic variables, species, communities, habitats, and ecosystems) is required to inform conservation scientists and planners. However, the spatial data required is often lacking. In this review, we aimed to address the status of our knowledge for 3 major types of spatial information: bathymetry, classification of marine habitats, and species distributions. To exemplify the data gaps and approaches to bridge them, we examined case studies that systematically prioritize conservation in the Mediterranean Sea. We found that at present the data required for conservation planning is generally more readily available and of better quality for the European countries located in the Western Mediterranean Sea. Additionally, the Mediterranean Sea is lagging behind other marine regions where rigorous criteria for conservation planning has been applied in the past 20 yr. Therefore, we call upon scientists, governments, and international governmental and non-governmental organizations to harmonize current approaches in marine mapping and to develop a framework that is applicable throughout the Mediterranean region. Such coordination between stakeholders is urgently needed before more countries undertake further extensive habitat mapping, so that future conservation planning can use integrated spatial datasets.
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Numéro d'Appel LL @ pixluser @ collection 383
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Auteur Shannon, L.; Coll, M.; Bundy, A.; Gascuel, D.; Heymans, J.J.; Kleisner, K.; Lynam, C.P.; Piroddi, C.; Tam, J.; TraversTrolet, M.; Shin, Y.
Titre Trophic level-based indicators to track fishing impacts across marine ecosystems Type Article scientifique
Année 2014 Publication Revue Abrégée Mar Ecol Prog Ser
Volume 512 Numéro Pages 115-140
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Résumé (up) ABSTRACT: Trophic level (TL)-based indicators have been widely used to examine fishing impacts in aquatic ecosystems and the induced biodiversity changes. However, much debate has ensued regarding discrepancies and challenges arising from the use of landings data from commercial fisheries to calculate TL indicators. Subsequent studies have started to examine survey-based and model-based indicators. In this paper, we undertake an extensive evaluation of a variety of TL indicators across 9 well-studied marine ecosystems by making use of model- as well as survey- and catch-based TL indicators. Using detailed regional information and data on fishing history, fishing intensity, and environmental conditions, we evaluate how well TL indicators are capturing fishing effects at the community level of marine ecosystems. Our results highlight that the differences observed between TL indicator values and trends is dependent on the data source and the TL cut-off point used in the calculations and is not attributable to an intrinsic problem with TL-based indicators. All 3 data sources provide useful information about the structural changes in the ecosystem as a result of fishing, but our results indicate that only model-based indicators represent fishing impacts at the whole ecosystem level.
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 1206
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Auteur Christensen, V.; Coll, M.; Piroddi, C.; Steenbeek, J.; Buszowski, J.; Pauly, D.
Titre A century of fish biomass decline in the ocean Type Article scientifique
Année 2014 Publication Revue Abrégée Mar Ecol Prog Ser
Volume 512 Numéro Pages 155-166
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Résumé (up) ABSTRACT: We performed a global assessment of how fish biomass has changed over the last 100 yr, applying a previously developed methodology using ecological modeling. Our assessment built on more than 200 food web models representing marine ecosystems throughout the world covering the period from 1880 to 2007. All models were constructed based on the same approach, and have been previously documented. We spatially and temporally distributed fish biomasses delivered by these models based on fish habitat preferences, ecology, and feeding conditions. From these distributions, we extracted over 68000 estimates of biomass (for predatory and prey fishes separately, including trophic level of 3.5 or higher, and trophic level between 2.0 and 3.0, respectively), and predicted spatial-temporal trends in fish biomass using multiple regression. Our results predicted that the biomass of predatory fish in the world oceans has declined by two-thirds over the last 100 yr. This decline is accelerating, with 54% occurring in the last 40 yr. Results also showed that the biomass of prey fish has increased over the last 100 yr, likely as a consequence of predation release. These findings allowed us to predict that there will be fish in the future ocean, but the composition of fish assemblages will be very different from current ones, with small prey fish dominating. Our results show that the trophic structure of marine ecosystems has changed at a global scale, in a manner consistent with fishing down marine food webs.
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Numéro d'Appel LL @ pixluser @ collection 379
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