Reacción en el tamaño de poliquetos del fondo marino frente a diferentes regímenes nutricionales

Analyses of body size of abyssal polychaetes were made from sites experiencing different levels of nutrient flux in the Pacific and Atlantic Oceans. Measuring polychaetes was problematical due to high levels of fragmentation, and width of the first chaetiger was used as a surrogate for body size. Results indicated that polychaetes were significantly smaller in Atlantic areas experiencing seasonal or periodic input of phytodetritus. This observation held not just for comparison of sizes of the total assemblage but also when comparisons were made at the family and species level. Not all families showed a response. In the Atlantic, individuals belonging to the families Cirratulidae, Spionidae and Sabellidae indicated size differences, while in the Pacific spionids were significantly smaller from phytodetrital sites. At the species level, six species - all deposit feeders - were significantly smaller from phytodetrital sites, while two nominally predator/omnivore species showed an increase in size. Two hypotheses for the size frequency of the Atlantic populations from phytodetrital sites are suggested – the juvenile recruitment hypothesis where the smaller population body size is because of an influx of newly recruited juveniles; and the allometric plasticity hypothesis which postulates a physiological response from populations from non-phytodetrital areas delaying reproduction and putting more energy into growth, hence resulting in a larger body size. It is hypothesised that the larger size in non-phytodetrital sites may be a response to starvation.Se han realizado análisis sobre el tamaño de algunos poliquetos de zonas abisales marinas con diferentes niveles de flujo de nutrientes en los océanos Atlántico y Pacífico. Dada la tendencia a romperse, la medición de dichos poliquetos fué problemática. Por esta razon, la anchura del primer chaetígero se ha tomado como sustituto del tamaño total. Los resultados indican que los poliquetos eran notablemente más pequeños en zonas donde el flujo de nutrientes era estacional u ocasional. Ésta observación no solo se aplica a la totalidad de la población, sino también al nivel taxonómico familiar y por especies. No todas las familias mostraron dicha relación. En el océano Atlántico, individuos pertenecientes a las familias Cirratulidae, Spionidae y Sabellidae mostraron diferencias de tamaño, mientras que en el océano Pacífico las familias Paraonidae y Spionidae eran de menor tamaño en zonas con aportación nutritiva. Al nivel de especie, seis especies, todas ellas detritívoras, eran más pequeñas en zonas con flujo de nutrientes, y otras dos especies, ambas consideradas carnívoras/omnívoras, eran más grandes en dichas donas. Un análisis de frecuencia de los distintos tamaños de poliquetos en estas zonas demuestran que el alto numero de tamaños menores no ha sido causado por una afluencia de juveniles. Se especula que el mayor tamaño de poliquetos encontrados en zonas con flujo de nutrientes estacional se debe a una reacción de inanición. &nbsp

A new species of Magelona (Polychaeta: Magelonidae) from southern Namibia

A new species of Magelonidae, Magelona debeerei sp. nov., is described and illustrated from grab-samples collected at <100moff the southwest coast of Africa. Magelona debeerei sp. nov. has previously been identified from the region as M. papillicornis (Müller, 1858) by Day (1955, 1961, 1967) but differs from M. papillicornis sensu stricto by possessing dorsal medial lobes on chaetigers 4–8 and lateral pouches (Σ configuration) between chaetigers 10 and 11. Three species of Magelona have now been recorded from southern Africa (M. capensis Day, 1961, M. cincta Ehlers, 1908 and M. debeerei sp. nov.), and a key to Magelona from this region is provided

Deep-sea ophiuroids (Echinodermata: Ophiuroidea: Ophiurida) from the Gulf of Cadiz (NE Atlantic)

The Ophiuroidea collected from mud volcanoes and adjacent bathyal environments from the Gulf of Cadiz are reviewed. Thirteen species from six families—Ophiacanthidae, Ophiactidae, Amphiuridae, Amphilepididae, Ophiuridae and Ophiolepididae— were identified. A direct relationship to the chemosynthetic assemblages has not been established as the ophiuroids found in the mud volcanoes do not appear to have novel morphological adaptations and also occur in non-reducing environments. The ophiuroid fauna from the Gulf of Cadiz differs from other cold seep regions not only by the high species richness but also because members of Amphiuridae are dominant both in number of species and abundance. One species previously unknown, Ophiopristis gadensis sp. nov., (Ophiacanthidae) was collected from a dead cold-water coral thicket at the flank of a mud volcano and differs from its congeners in the type of disk spines which are more rugose and not smooth as in most of the other species, the presence of the thickened integument in larger specimens and the distinct separation between the oral papillae and the second oral tentacle scales.European Commission - GOCE-CT-2005-511234FCT- SFRH/BD/17085/2004HERMES projec

Inter-annual species-level variations in an abyssal polychaete assemblage (Sta. M, NE Pacific, 4000 m)

Understanding the dynamics of abyssal community structure and function has become increasingly important as deep-sea resource exploitation and climate change pressures are expected to ramp up. This time-series study investigates macrofaunal polychaete dynamics at a station in the North East Pacific (Sta. M; 35˚ N 123˚ W, 4000 m, 1991-2011). Infaunal polychaete species were identified and their proxy biomass and proxy energy use rate estimated. The assemblage comprised 167 species, having a composition consistent with other abyssal areas globally. Significant changes in univariate and multivariate parameters (rank abundance distribution, Simpson’s diversity index, and species and functional group composition) were detected across 1991-2011. However, no change in biomass or energy use rate was apparent through the time-series. The largest changes in the polychaete assemblage coincided with both an increase in sinking particulate organic carbon flux to the seafloor in 2007, and a 40 km relocation of the sampling location to a site 100 m shallower, preventing a conclusive assessment of which might drive the observed variation. Analyses prior to the change of sampling location showed that the polychaete assemblage composition dynamics were primary driven by food supply variation. Changes in several species were also lagged to changes in POC flux by 4 to 10 months. The polychaete fauna exhibited a significant positive relationship between total density and total energy use rate, suggesting population-level tracking of a common resource (e.g. POC flux food supply). Neither compensatory nor energetic zero-sum dynamics were detected among the polychaete assemblage, but the results suggest that the latter occur in the macrofaunal community as a whole. The results do indicate (a) potential control of species composition, and the density of individual key species, by food supply, when the time-series prior to the sampling location was analysed separately, and (b) generally sensitive detection of environmental change by species-level analysis of the abyssal polychaete assemblage

Performance of cages as large animal-exclusion devices in the deep sea

Sedimentary, deep-sea communities include megafaunal animals (e.g., sea cucumbers, brittle stars, crabs) and demersal fishes, collectively termed the large, motile epifauna (LME). Individuals of the LME are common, and their biomass approximates that of the macrofauna. Based on analogies with shallow-water animals, they are likely to be sources of mortality for the infauna and to create spatial and temporal heterogeneity in the community. Given present theories of deep-sea community organization, such effects could be important. Unfortunately, this hypothesis has not been tested because of the difficulty of conducting experiments in the deep sea and because tools for manipulating the LME have not been developed. We studied the suitability of exclusion cages for this purpose at 780 m depth in San Diego Trough. We placed 16 cages of two mesh sizes for 4.5 months over regions of the seafloor that appeared free of LME. Time-lapse photographs of a cage and a control plot coupled with observations of all cages at the end of the experiment indicated that small (1.27-cm × 1.27-cm square)-mesh cages were effective at excluding LME. Further, the cages were essentially free of cage artifacts that have been reported in shallow-water studies. Large, mobile and disruptive animals (e.g., fishes, crabs) did not establish long-term residence adjacent to or on the cages. Bio-fouling slightly reduced the open surface area of the cage mesh, potentially reducing flow through the cage, but the composition of surface sediments in terms of organic C and N, phytoplankton-derived pigments, and grain size was indistinguishable between cages and control areas. Activities of excess 234Th were significantly higher (average = 37%) inside of small-mesh cages, which might suggest enhanced particulate deposition inside cages. However, this measurement was an artifact of experimental manipulation. Particles that accumulated on the cage during the experiment were dislodged and settled to the seafloor when the cage was opened just prior to sampling. These particles would have been highly enriched in 234Th, and their inclusion in core samples artificially inflated the calculated sediment accumulation rates inside cages. Therefore, the cages performed well; they excluded the targeted LME without causing artifacts and thus should be useful for experimental study of a group of animals that may have substantial impact on the structure and organization of deep-sea communities

Reorganization of Atlantic Waters at sub-polar latitudes linked to deep-water overflow in both glacial and interglacial climate states

While a large cryosphere may be a necessary boundary condition for millennial-scale events to persist, a growing body of evidence from previous interglacial periods suggests that high-magnitude climate events are possible during low-cryosphere climate states. However, the full spectrum of variability, and the antecedent conditions under which such variability can occur, have not been fully described. As a result, the mechanisms generating high-magnitude climate variability during low-cryosphere boundary conditions remain unclear. In this study, high-resolution climate records from Deep Sea Drilling Project (DSDP) site 610 are used to portray the North Atlantic climate's progression through low ice, boundary conditions of Marine Isotope Stage (MIS) 11c into the glacial inception. We show that this period is marked by two climate events displaying rapid shifts in both deep overflow and surface climate. The reorganization between Polar Water and Atlantic Water at subpolar latitudes appears to accompany changes in the flow of deep water emanating from the Nordic Seas, regardless of magnitude or boundary conditions. Further, during both intermediate and low ice boundary conditions, we find that a reduction in deep water precedes surface hydrographic change. The existence of surface and deep-ocean events, with similar magnitudes, abruptness, and surface–deep phasing, advances our mechanistic understanding of, and elucidates antecedent conditions that can lead to, high-magnitude climate instability.publishedVersio

Community-Acquired Klebsiella pneumoniae Bacteremia: Global Differences in Clinical Patterns

We initiated a worldwide collaborative study, including 455 episodes of bacteremia, to elucidate the clinical patterns of Klebsiella pneumoniae. Historically, community-acquired pneumonia has been consistently associated with K. pneumoniae. Only four cases of community-acquired bacteremic K. pneumoniae pneumonia were seen in the 2-year study period in the United States, Argentina, Europe, or Australia; none were in alcoholics. In contrast, 53 cases of bacteremic K. pneumoniae pneumonia were observed in South Africa and Taiwan, where an association with alcoholism persisted (p=0.007). Twenty-five cases of a distinctive syndrome consisting of K. pneumoniae bacteremia in conjunction with community-acquired liver abscess, meningitis, or endophthalmitis were observed. A distinctive form of K. pneumoniae infection, often causing liver abscess, was identified, almost exclusively in Taiwan

Reorganization of Atlantic Waters at sub-polar latitudes linked to deep-water overflow in both glacial and interglacial climate states

While a large cryosphere may be a necessary boundary condition for millennial-scale events to persist, a growing body of evidence from previous interglacial periods suggests that high-magnitude climate events are possible during low-cryosphere climate states. However, the full spectrum of variability, and the antecedent conditions under which such variability can occur, have not been fully described. As a result, the mechanisms generating high-magnitude climate variability during low-cryosphere boundary conditions remain unclear. In this study, high-resolution climate records from Deep Sea Drilling Project (DSDP) site 610 are used to portray the North Atlantic climate's progression through low ice, boundary conditions of Marine Isotope Stage (MIS) 11c into the glacial inception. We show that this period is marked by two climate events displaying rapid shifts in both deep overflow and surface climate. The reorganization between Polar Water and Atlantic Water at subpolar latitudes appears to accompany changes in the flow of deep water emanating from the Nordic Seas, regardless of magnitude or boundary conditions. Further, during both intermediate and low ice boundary conditions, we find that a reduction in deep water precedes surface hydrographic change. The existence of surface and deep-ocean events, with similar magnitudes, abruptness, and surface–deep phasing, advances our mechanistic understanding of, and elucidates antecedent conditions that can lead to, high-magnitude climate instability.publishedVersio

Light Vector Mesons in the Nuclear Medium

The light vector mesons ($\rho$, $\omega$, and $\phi$) were produced in deuterium, carbon, titanium, and iron targets in a search for possible in-medium modifications to the properties of the $\rho$ meson at normal nuclear densities and zero temperature. The vector mesons were detected with the CEBAF Large Acceptance Spectrometer (CLAS) via their decays to $e^{+}e^{-}$. The rare leptonic decay was chosen to reduce final-state interactions. A combinatorial background was subtracted from the invariant mass spectra using a well-established event-mixing technique. The $\rho$ meson mass spectrum was extracted after the $\omega$ and $\phi$ signals were removed in a nearly model-independent way. Comparisons were made between the $\rho$ mass spectra from the heavy targets ($A > 2$) with the mass spectrum extracted from the deuterium target. With respect to the $\rho$-meson mass, we obtain a small shift compatible with zero. Also, we measure widths consistent with standard nuclear many-body effects such as collisional broadening and Fermi motion.Comment: 15 pages, 18 figures, 3 table