Rol ecosistémico de Malacobelemnon daytoni (Octocorallia, Pennatulacea, Kophobelemnidae) en comunidades bentónicas de Caleta Potter, Isla 25 de Mayo, Antártida.

Tesis (Grado Doctor en Ciencias Biológicas)--Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Lugar de Trabajo:: Departamento de Diversidad Biológica y Ecología. Ecología Marina- CONICET-Universidad Nacional de Córdoba. 2014 - 123 h. con Anexo de Publicaciones Derivada de la Tesis + CD. ils.; grafs.; tabls.; maps. Contiene Referencia Bibliográfica. Abstract en español e inglésEl ecosistema bentónico de Caleta Potter (Isla 25 de Mayo, Antártida) mostró en los últimos años un aumento llamativo en la abundancia y rango de distribución del cnidario Malacobelemnon daytoni (Octocorallia, Pennatulacea, Kophobelemnidae) junto con la retracción de especies de ascidias. En paralelo a estos cambios en las comunidades bentónicas, se registró un incremento de sedimento en la columna de agua como consecuencia del retroceso del Glaciar Fourcade debido al aumento de las temperaturas atmosféricas en la región.Este es el primer caso registrad donde pennatulaceos son dominantes, más aún, esta especie no ha sido reportada en ningún otro ecosistema antártico. El presente trabajo tiene como objetivo analizar la biología del cnidario mediante los estudios de reproducción, alimentación y tolerancia al sedimento, para inferir acerca del potencial de super vivencia de esta especie frente al cambio ambiental que se viene registrando en este ecosistema. Se realizaron experimentos de tolerancia al sedimento en la base Argentina Carlini, donde además se tomaron muestras durante dos años consecutivos (2009-2010) para los estudios de reproducción y alimentación. Se observó que Malacobelemnon daytoni es una especie gonocórica, de fecundación externa y larvas lecitotróficas. La madurez reproductiva en esta especie se alcanza rápidamente (1, 5 cm de longitud) y la oogénesis se caracteriza por el mantenimiento de oocitos en diferentes estadios durante todo el año, de los cuales una pequeña proporción finaliza la maduración y son liberados de manera sincronizada a través de los autozoides. Se sugiere que la reproducción es estacional con más de un desove al año, asociados a los pulsos de energía generados a partir de los detritos puestos a disposición en los eventos de resuspensión. Con respecto a la estrategia alimentaria se observó coincidencia entre los dos marcadores tróficos utilizados (Ácidos Grasos e isótopos estables de C y N) señalando a esta especie como omnívora/oportunista. Estos resultados, junto con los análisis de hidratos de carbono, proteínas y lípidos refuerzan la hipótesis de que los eventos de resuspensión son una fuente importante de energía que hacen que la estacionalidad, en cuanto a los periodos de agotamiento de alimento en otoño e invierno, no sea tan marcada. Por último, se observó que la especie no se ve afectada frente a concentraciones de sedimento, aún muy por encima de las registradas actualmente en la caleta. Estos resultados en comparación con los realizados en otras especies de Caleta Potter (ascidias y el bivalvo Laternula elliptica) sugieren que la sedimentación puede estar jugando un papel importante en los cambios observados en las comunidades bentónicas, favorecien do a Malacobelemnon daytoni de manera indirecta al actuar fuertemente sobre otras especies, principalmente en ascidias. Esto conjuntamente con el éxito reproductivo (madurez temprana y más de un desove anual), y la amplia variedad de fuentes de alimento en su dieta, dan los primeros resultados que ayudan a comprender el llamativo éxito ecológico de esta especie en Caleta Potter

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Extended glacier retreat is among the main consequences of the rapid warming of the West Antarctic Peninsula. Particularly, in the inner part of Potter Cove (South Shetland Islands, Antarctica) large areas are now exposed to open sea conditions owing to the retreat of Fourcade glacier. During the 2010 austral summer, underwater photographic surveys were undertaken by SCUBA diving up to 30 m in these new ice-free areas 80 m from the glacier front. Our main aim was to investigate colonization and early succession of the benthic assemblages on soft-bottom areas. Here, we reported a total of 1,146 animals belonging to 13 taxa. Filter-feeders comprised the largest trophic group and sessile fauna showed much higher coverages and densities than mobile fauna at all depths. The most abundant groups were ascidians and bryozoans, which together comprised ~90% of all taxa documented. In a region where most of marine-terminating glaciers are in retreat, these results are an important contribution to improve our knowledge on colonization in the newly ice-free areas

Molecular responses of a key Antarctic species to sedimentation due to rapid climate change

Rapid regional warming causing glacial retreat and melting of ice caps in Antarctica leads benthic filter-feeders to be exposed to periods of food shortage and high respiratory impairment as a consequence of seasonal sediment discharge in the West Antarctic Peninsula coastal areas. The molecular physiological response and its fine-tuning allow species to survive acute environmental stress and are thus a prerequisite to longer-term adaptation to changing environments. Under experimental conditions, we analyzed here the metabolic response to changes in suspended sediment concentrations, through transcriptome sequencing and enzymatic measurements in a highly abundant Antarctic ascidian. We found that the mechanisms underlying short-term response to sedimentation in Cnemidocarpa verrucosa sp. A involved apoptosis, immune defense, and general metabolic depression. These mechanisms may be understood as an adaptive protection against sedimentation caused by glacial retreat. This process can strongly contribute to the structuring of future benthic filter-feeder communities in the face of climate change.Fil: Ruiz, Micaela Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; ArgentinaFil: Servetto, Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; ArgentinaFil: Alurralde, Roque Gastón. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; ArgentinaFil: Abele, Doris. Alfred-Wegener-Institut. Helmholtz-Zentrum für Polar und Meeresforschung; AlemaniaFil: Harms, Lars. Alfred-Wegener-Institut. Helmholtz-Zentrum für Polar und Meeresforschung; AlemaniaFil: Sahade, Ricardo Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; ArgentinaFil: Held, Christoph. Alfred-Wegener-Institut. Helmholtz-Zentrum für Polar und Meeresforschung; Alemani

Climate change and glacier retreat drive shifts in an Antarctic benthic ecosystem

The Antarctic Peninsula (AP) is one of the three places on Earth that registered the most intense warming in the last 50 years, almost five times the global mean. This warming has strongly affected the cryosphere, causing the largest ice-shelf collapses ever observed and the retreat of 87% of glaciers. Ecosystem responses, although increasingly predicted, have been mainly reported for pelagic systems. However, and despite most Antarctic species being benthic, responses in the Antarctic benthos have been detected in only a few species, and major effects at assemblage level are unknown. This is probably due to the scarcity of baselines against which to assess change. We performed repeat surveys of coastal benthos in 1994, 1998, and 2010, analyzing community structure and environmental variables at King George Island, Antarctica. We report a marked shift in an Antarctic benthic community that can be linked to ongoing climate change. However, rather than temperature as the primary factor, we highlight the resulting increased sediment runoff, triggered by glacier retreat, as the potential causal factor. The sudden shift from a “filter feeders–ascidian domination” to a “mixed assemblage” suggests that thresholds (for example, of tolerable sedimentation) and alternative equilibrium states, depending on the reversibility of the changes, could be possible traits of this ecosystem. Sedimentation processes will be increasing under the current scenario of glacier retreat, and attention needs to be paid to its effects along the AP

Reproductive Seasonality of the Antarctic Sea Pen Malacobelemnon daytoni (Octocorallia, Pennatulacea, Kophobelemnidae).

The pennatulid Malacobelemnon daytoni is one of the dominant species in Potter Cove, Antarctica. Its abundance and range of distribution have increased in recent years probably related to climate change mediated alterations of environmental factors. This work is the second part of a study dealing on the reproductive ecology of Malacobelemnon daytoni, and aims to assess its reproductive seasonality over a two-year period. Sampling was carried out every month during 2009-2010 and samples were examined by histological analysis. Gametogenesis exhibited a seasonal pattern evidenced by the maturity stage index (MSI) and the number of mature oocytes and cysts throughout the year. Immature oocytes and spermatocytes were present year-round, but maturation was seasonal and it seems that more than one spawning per year was possible. These spawnings could be more linked with suspended particulate matter (SPM) (probably available via resuspension events) than with primary production pulses. This idea reinforces the hypothesis that winter time is not so stressful, in energy terms, in Potter Cove, which seems to depend on energy sources other than local phytoplankton production. There was not a strong inter-annual variability between the reproductive characteristics analyzed in 2009 and 2010; the only variable different was the size of oocytes (higher in 2009), suggesting different energy availability in each year, related with a higher concentration of SPM in 2009 (although it was not significant). Malacobelemnon daytoni could be the first reported Antarctic suspension feeder species that presents a reproductive cycle with more than a spawning event per year. This strategy would help to explain the success of this species in the Potter Cove ecosystem and in high ice-impacted areas

Oocytes and cysts size and environmental variation.

<p>(A) Mean oocyte feret diameter (μm) (black line) and average spermatic cyst size (μm) (dashed line). (B) Seasonal variation of Chlorophyll-a (mg.m^-3) and (C) SPM (mg.m^-3) data was collected by 4.7 l Niskin bottles at 5 depths (0; 5; 10; 20 and 30m) and determined by Schloss el at. (2012) Vertical bars indicate ± SE.</p

Oocytes and spermatic size distribution.

<p>(A) Mean spermatic cyst size (n = 265 basal; n = 1647 middle and n = 790 apical) and (B) oocyte feret diameter distribution in each of the colony sections: basal, middle and apical (n = 645 basal; n = 3801 middle and n = 880 apical). Vertical bars indicate ± SE. Letters indicate groups of the <i>a posterior</i> multiple range test (<i>p</i>< 0.05).</p

Maturity stage index and fecundity.

<p>(A) Maturity stage index (MSI); (B) effective relative fecundity (ERF) in females and males and (C) average number of mature, at stage I and II oocytes, between January and December 2009 and 2010. Vertical bars indicate ± SE.</p

Relative frequency of oocyte size classes in colonies collected between January 2009 and December 2010.

<p>The <i>vertical arrow</i> indicates the absence of mature oocytes >200 μm. Vertical bars indicate ± SE.</p