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Diel Vertical Dynamics of Gelatinous Zooplankton (Cnidaria, Ctenophora and Thaliacea) in a Subtropical Stratified Ecosystem (South Brazilian Bight)

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      Abstract

      The diel vertical dynamics of gelatinous zooplankton in physically stratified conditions over the 100-m isobath (~110 km offshore) in the South Brazilian Bight (26°45’S; 47°33’W) and the relationship to hydrography and food availability were analyzed by sampling every six hours over two consecutive days. Zooplankton samples were taken in three depth strata, following the vertical structure of the water column, with cold waters between 17 and 13.1°C, influenced by the South Atlantic Central Water (SACW) in the lower layer (>70 m); warm (>20°C) Tropical Water in the upper 40 m; and an intermediate thermocline with a deep chlorophyll-a maximum layer (0.3–0.6 mg m-3). Two distinct general patterns were observed, emphasizing the role of (i) physical and (ii) biological processes: (i) a strong influence of the vertical stratification, with most zooplankton absent or little abundant in the lower layer. The influence of the cold SACW on the bottom layer apparently restricted the vertical occupation of most species, which typically inhabit epipelagic warm waters. Even among migratory species, only a few (Aglaura hemistoma, Abylopsis tetragona eudoxids, Beroe sp., Thalia democratica, Salpa fusiformis) crossed the thermocline and reached the bottom layer. (ii) A general tendency of partial migrations, with variable intensity depending on the different species and developmental stages; populations tended to be more widely distributed through the water column during daylight, and to become more aggregated in the upper layer during the night, which can be explained based on the idea of the “hunger-satiation hypothesis”, maximizing feeding and minimizing the chances of being predated.

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      Eat and run? The hunger/satiation hypothesis in vertical migration: history, evidence and consequences.

      The study of vertical migrations in aquatic organisms has a long and colourful history, much of it to do with the effects of changing sampling technology on our understanding of the phenomenon. However, the overwhelming majority of such studies carried out today still depend on detecting differences in vertical distribution profiles during some course of time, or acoustic echoes of migrating bands of organisms. These can not distinguish migratory activity of individual organisms, but can only assess net results of mass transfers of populations, which may integrate many individual migrations. This is an important distinction, for without knowing the actual movements of individuals it seems unlikely that we will be able to understand their causes, nor the effects of vertical migrations on the environment or on the migrators themselves. This review examines evidence for individual vertical movements gathered from 'tracers', mainly gut contents, and reviews the evidence for the hypothesis that such movements are in fact driven by hunger and satiation. The more recently appreciated vertical migrations of phytoplankters and their similarities in form and driving forces to those of zooplankton and nekton are also discussed. Finally, the role of vertical migrators in vertical fluxes of materials is discussed, along with the consequences of satiation-driven descent for such estimates.
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        Marine zooplankton studies in Brazil: a brief evaluation and perspectives

         Rubens Lopes (2007)
        Marine zooplankton research in Brazil has been primarily descriptive, with most studies focusing on community structure analysis and related issues. The composition and spatial distribution of several taxonomic groups are currently well known, although less-abundant and small-sized taxa as well as initial stages of almost all species have received little attention. Some numerically important taxa such as heterotrophic protists, ctenophores, acoel turbellarians and ostracods remain virtually unstudied. Large sectors of the continental shelf have not been sampled in detail, particularly those areas influenced by the North Brazil Current (5ºN-15ºS). Zooplankton abundance and biomass in offshore waters have seldom been quantified, and information on the distribution and vertical migration of meso- and bathypelagic species are lacking. Additional faunistic assessments must target those less-studied taxa and geographical locations. However, priority in ecological studies should be given to process-oriented investigations aimed at understanding the mechanisms controlling zooplankton distribution, trophic interactions within pelagic food webs and production cycles in relation to the physical environment. An effort should be made to incorporate state-of-the-art sampling technology and analytical methods into future research projects.
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          Electrically coupled, photosensitive neurons control swimming in a jellyfish.

          Central neurons in Polyorchis (Hydromedusae) were impaled with microelectrodes, and conventional resting potentials were obtained. The waveform of action potentials recorded concurrently with swimming events shows evidence of electrotonic coupling between these neurons, which are also directly photosensitive and receive excitatory synaptic input from other conduction systems.
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            Author and article information

            Affiliations
            [1 ]Departamento de Sistemática e Ecologia, Universidade Federal da Paraíba, João Pessoa, Paraíba, Brasil
            [2 ]Departamento de Oceanografia Biológica, Instituto Oceanográfico, Universidade de São Paulo, São Paulo, Brasil
            [3 ]Programa de Pós Graduação em Zoologia, Departamento de Zoologia, Universidade Federal do Paraná, Curitiba, Paraná, Brasil
            The Evergreen State College, UNITED STATES
            Author notes

            Competing Interests: The authors have declared that no competing interests exist.

            Conceived and designed the experiments: MNJ JCUC FPB. Performed the experiments: MNJ JCUC. Analyzed the data: MNJ FPB. Contributed reagents/materials/analysis tools: MNJ FPB. Wrote the paper: MNJ FPB. Identification and quantification of gelatinous zooplankton: MNJ. Identification and quantification of other zoplankton groups: MNJ JCUC.

            Contributors
            Role: Editor
            Journal
            PLoS One
            PLoS ONE
            plos
            plosone
            PLoS ONE
            Public Library of Science (San Francisco, CA USA )
            1932-6203
            4 December 2015
            2015
            : 10
            : 12
            26637179
            4670095
            10.1371/journal.pone.0144161
            PONE-D-15-08537
            (Editor)
            © 2015 Nogueira Júnior et al

            This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

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            Figures: 12, Tables: 3, Pages: 28
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            Funding
            This study was undertaken as part of the PROPELL project (Dinâmica das interações físico-biológicas no sistema pelágico da plataforma continental Sudeste do Brasil), supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq.; www.cnpq.br, project n° 474165/2004-3). This investigation also received funds from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP; http://www.fapesp.br/, project n° 2011/21290-1). MNJ had a scholarship from CNPq (PhD grant n° 140945/2007-5) and from FAPESP (post-doctoral grant n° 2011/09880-8 and JCUC from the USA National Science Foundation ( http://www.nsf.gov/, Grant GEO-0452325) through the Inter-American Institute of Global Change Research ( http://www.iai.int/, grant CRN 2076). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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