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      The impact of a strong natural hypoxic event on the toadfish Aphos porosus in Coliumo Bay, south-central Chile Translated title: Impacto de un fuerte evento de hipoxia natural sobre el bagre de mar Aphos porosus en Bahía Coliumo, centro-sur de Chile

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          Abstract

          The occurrence of natural hypoxic events and coastal marine areas affected by anthropogenic hypoxia has increased over the past decades. In Coliumo Bay, a small shallow bay of the eastern South Pacific, an intense event of natural hypoxia took place in January 2008, causing the mass mortality of fish and other components of the benthic and pelagic communities. In the short term (3 months) recovery was observed in species richness as well as in total fish density. Nevertheless, in the medium term (2 years), this event produced negative effects on population size. In particular, the toadfish Aphos porosus, a dominant fish species in Coliumo Bay, showed a progressive decrease in population size since the occurrence of the hypoxic event, associated with a decrease in recruitment. We hypothesized that this reduction in population size lowered the probability of encounter of reproductive adults, decreasing the number of eggs, larvae and ultimately recruits, thus driving the population towards a low density threshold, and eventually, favoring an Allee effect condition. These results provide evidence on the causal relationship between coastal natural hypoxic events, mass mortality, life history and population dynamics. The slow recovery of the A. porosus population size suggests a process in which the population remains vulnerable to new perturbations. The observed population response is an example of the trajectory that some species may follow when faced with increasing occurrences of natural hypoxic events as predicted, for instance, by global warming scenarios.

          Translated abstract

          La ocurrencia de hipoxias naturales y las áreas marinas costeras afectadas por hipoxias antropogénicas se han incrementando en las últimas décadas. En Coliumo, una pequeña bahía somera del Pacífico sur-este, se registró un intenso evento de hipoxia natural en enero del 2008, provocando una mortalidad masiva de peces y otros componentes de la comunidad bentónica y pelágica. En el corto plazo (3 meses) se observó una recuperación en la riqueza y densidad total de peces, sin embargo, en el mediano plazo (2 años) este evento tuvo efectos negativos en sus tamaños poblacionales. En particular Aphos porosus, especie dominante del ensamble de peces en los fondos blandos de Bahía Coliumo, presentó una disminución progresiva en su tamaño poblacional luego del evento, asociada a una disminución en el reclutamiento. Nuestra hipótesis es que la reducción del tamaño poblacional, habría disminuido la probabilidad de encuentro de adultos reproductivos, disminuyendo huevos, larvas y finalmente los reclutas, llevando a A. porosus hacia un umbral crítico de baja densidad, favoreciendo una condición poblacional de efecto Allee. Estos resultados entregan evidencia sobre la relación de causalidad entre eventos de hipoxia natural, mortalidad masiva, historia de vida y dinámica poblacional. La lenta recuperación numérica de A. porosus sugiere un proceso en el cual la población presenta una alta vulnerabilidad a nuevas perturbaciones. Esta respuesta poblacional es un ejemplo de la trayectoria que ciertas especies pudieran seguir ante el incremento de eventos de hipoxia natural, el cual se estima podría ocurrir en un escenario de calentamiento global.

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          Biostatistical Analysis

          Designed for one/two-semester, junior/graduate-level courses in Biostatistics, Biometry, Quantitative Biology, or Statistics, the latest edition of this best-selling biostatistics text is both comprehensive and easy to read. It provides a broad and practical overview of the statistical analysis methods used by researchers to collect, summarize, analyze, and draw conclusions from biological research data. The Fourth Edition can serve as either an introduction to the discipline for beginning students or a comprehensive procedural reference for today's practitioners.
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            Dead zones in the coastal oceans have spread exponentially since the 1960s and have serious consequences for ecosystem functioning. The formation of dead zones has been exacerbated by the increase in primary production and consequent worldwide coastal eutrophication fueled by riverine runoff of fertilizers and the burning of fossil fuels. Enhanced primary production results in an accumulation of particulate organic matter, which encourages microbial activity and the consumption of dissolved oxygen in bottom waters. Dead zones have now been reported from more than 400 systems, affecting a total area of more than 245,000 square kilometers, and are probably a key stressor on marine ecosystems.
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              Thresholds of hypoxia for marine biodiversity.

              Hypoxia is a mounting problem affecting the world's coastal waters, with severe consequences for marine life, including death and catastrophic changes. Hypoxia is forecast to increase owing to the combined effects of the continued spread of coastal eutrophication and global warming. A broad comparative analysis across a range of contrasting marine benthic organisms showed that hypoxia thresholds vary greatly across marine benthic organisms and that the conventional definition of 2 mg O(2)/liter to designate waters as hypoxic is below the empirical sublethal and lethal O(2) thresholds for half of the species tested. These results imply that the number and area of coastal ecosystems affected by hypoxia and the future extent of hypoxia impacts on marine life have been generally underestimated.
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                Author and article information

                Journal
                revbiolmar
                Revista de biología marina y oceanografía
                Rev. biol. mar. oceanogr.
                Universidad de Valparaíso. Facultad de Ciencias del Mar (Valparaíso, , Chile )
                0718-1957
                December 2012
                : 47
                : 3
                : 475-487
                Affiliations
                [02] Concepción orgnameUniversidad de Concepción orgdiv1Centro de Investigación Oceanográfica en el Pacífico Sur Oriental (COPAS) Chile
                [01] Concepción orgnameUniversidad de Concepción orgdiv1Facultad de Ciencias Naturales y Oceanográficas orgdiv2Programa de Investigación Marina de Excelencia Chile eduhernandez@ 123456udec.cl
                [03] Concepción orgnameUniversidad de Concepción orgdiv1Facultad de Cs. Naturales y Oceanográficas orgdiv2Departamento de Oceanografía Chile
                Article
                S0718-19572012000300010 S0718-1957(12)04700310
                10.4067/S0718-19572012000300010
                a6590a5b-7b69-4cf1-a3ad-191f71fbfc2c

                This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

                History
                : 01 June 2012
                : 05 November 2012
                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 63, Pages: 13
                Product

                SciELO Chile


                surgencia,hypoxia,Allee effect,Humboldt Current System,Sistema de Corriente Humboldt,efecto Allee,hipoxia,Fish,upwelling,Peces

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