Benthic community productivity in the Magellan region and in the Weddell Sea

Our comparison of macrobenthic biomass, production and productivity of the Magellan region (14 - 349 m water depth) and the Weddell Sea (132 - 548 m water depth) is based on multi box corer samples collected in both areas. Biomass is slightly but not significantly lower in the Magellan region (7.3 g C m-2) than in the Weddell Sea (12.0 g C m-2). Annual production and P/B ratio are higher in the Magellan region (5.1 g C m-2 y-1, 0.7 y-1) as compared to the Weddell Sea (3.6 g C m-2 y-1, 0.3 y-1). In the Magellan region, Mollusca, Polychaeta and Arthropoda dominate benthic production, whereas in the Weddell Sea Polychaeta, Porifera and Echinodermata are the most productive taxa

Growth and age of the Antarctic bryozonan Cellaria incula on the Weddell Sea shelf

*tbrey~a~~z-bremerhaven de Abstract: We analysed growth of the arborescent Antarctic cheilostoine bryozoan Cellaria incula by stable carbon and oxygen isotope analysis. The growth of one complete branch of C. incula takes one year, i.e. owing to the bifurcate colony structure two new branches grow froin each branch of the previous generation, The maximum age of a C. incula colony is likely to be more than 14 years. Annual production-to-biomass ratio is 0.67, the highest value hitherto measured for any benthic invertebrate south of 62"s. Comparatively fast growth and high productivity identi @ C. zncula as a pioneer species which is able to quickly occupy spatial niches produced by iceberg scouring on the Antarctic shelf

Activation of myosin V–based motility and F-actin–dependent network formation of endoplasmic reticulum during mitosis

It is widely believed that microtubule- and F-actin–based transport of cytoplasmic organelles and membrane fusion is down-regulated during mitosis. Here we show that during the transition of Xenopus egg extracts from interphase to metaphase myosin V–driven movement of small globular vesicles along F-actin is strongly inhibited. In contrast, the movement of ER and ER network formation on F-actin is up-regulated in metaphase extracts. Our data demonstrate that myosin V–driven motility of distinct organelles is differently controlled during the cell cycle and suggest an active role of F-actin in partitioning, positioning, and membrane fusion of the ER during cell division

Weddell Sea benthic communities under the influence of different ice regimes

Ice in its different forms affects benthic communities in Polar Regions directly and indirectly. In order to recognize effects of ice on benthic communities we analyzed benthos in four regions of the Weddell Sea: a) the southeastern Weddell Sea shelf (SEWSS); b) the Filchner-Rønne Outflow System (FROS); c) the Larsen A/B embayments; and d) the tip of the Antarctic Peninsula. These regions differ considerably in their ice regimes: The SEWSS is a typical high Antarctic habitat, influenced by seasonal sea ice coverage; the FROS is influenced by seasonal ice on its eastern edge, but under heavy year round ice conditions on its western edge; the Larsen A/B embayments were covered for hundreds of years by thick ice shelves, which recently disintegrated providing large areas for recolonization by benthos; and the shelf around the tip of the Antarctic Peninsula which can be considered as being unaffected by ice. Benthos in these four regions revealed distinct differences in abundance, biomass, and production values. Highest abundance values were found at the tip of the Antarctic Peninsula and along the SEWSS (2,767 and 2,535ind.m-2, respectively), whereas the lowest abundance corresponded to the Larsen A/B region (682ind.m-2). In terms of both, biomass and production, the southeastern Weddell Sea region showed the highest values (3,944.2g wet weight.m-2 and 10.3g C.y-1m-2, respectively), whereas the lowest values were found at Larsen A/B (71.08g.m-2 and 1.62g C.y-1.m-2) and FROS regions (71.08g.m-2 and 1.62 g C.y-1.m-2). A PERMANOVA showed the differences among regions to be significant in all three terms: abundance (Pseudo F=7.10; p=0.001), biomass (Pseudo F=6.01; p=0.001), and production (Pseudo F=6.28; p=0.001). These differences were mainly caused by sponges, ophiuroids and polychaetes. This study also shows pronounced differences in the structure, composition of the benthic communities in the four regions. We hypothesize that these differences are primarily due to the different sea-ice regimes in the regions

Trophic structure of shallow-water benthic communities in the sub-Antarctic Strait of Magellan

Trophic structure is among the most fundamental characteristics of an ecosystem since it is a useful way to determine the main energy flow at the ecosystem level. In the Magellan Strait, the local spatial heterogeneity at the shallow-waters ecosystems may have a great variety of potential food sources; however, knowledge about their biological communities and their structure is still unclear. We examined the trophic structure of shallow-water-mixed bottom communities at two sites in the sub-Antarctic Magellan Strait based on carbon (d13 C) and nitrogen (d15 N) stable isotope ratios. The benthic communities were composed of 46 species from 20 major taxa at Bahı´a Laredo (BL) and 55 species from 18 major taxa at Punta Santa Ana (PSA). Benthic macroalgae and organic matter associated with sediment are the major primary food sources at both sites. Although both sites are quite similar in their food sources and in their vertical trophic structure (C three trophic levels), the food web structure varied distinctly. Functionally, predators and grazers dominated both communities, but top predators were shorebirds, carnivore anemones and predatory nemerteans at BL, and sea stars, shorebirds, crabs and fishes at PSA. The distinct differences in the trophic structure at BL and PSA highlight the important variability of d15 N at the base of the benthic food web, the role of local environmental conditions and community dynamics in structuring shallow-water communities

Benthic communities of the Filchner Region (Weddell Sea, Antarctica)

Due to extreme pack ice, the Filchner Region in the southern Weddell Sea is one of the least studied regions on the planet. Here, we provide a detailed description of the benthic communities of this high-Antarctic ecosystem, and assess the relationship between environmental factors and benthic distribution patterns. Fieldwork was performed in the austral summers of 2013-14 and 2015-16 during the R/V ‘Polarstern’ cruises PS82 and PS96. Using a combination of multibox corer (MBC) and seabed image data from 37 stations (water depths 243-1217 m), we differentiated 6 station groups. While 1 of these groups was comprised of a single station, the other 5 groups represented distinct benthic communities. Three of these correspond to the previously described Eastern Shelf, Southern Shelf, and Southern Trench communities. However, we found distribution shifts and MBC abundance and biomass reductions when comparing our results with earlier studies. The other 2 groups have novel characteristics and are presented here as an Ice/Ice Shelf Water-related community and a Continental slope community. Water depth in combination with 2 or 3 other environmental variables (out of 7 available) explained <30% of the benthic distribution and composition. We found a tighter relationship between water mass circulation and spatial distribution of the communities; we suggest using water-mass-related characteristics (e.g. productivity regimes, water currents) to better explain benthic spatial distribution patterns

Testing the preservation potential of early diagenetic dolomites as geochemical archives

Early marine diagenetic dolomite is a rather thermodynamically‐stable carbonate phase and has potential to act as an archive of marine porewater properties. However, the variety of early to late diagenetic dolomite phases that can coexist within a single sample can result in extensive complexity. Here, the archive potential of early marine dolomites exposed to extreme post‐depositional processes is tested using various types of analyses, including: petrography, fluid inclusion data, stable δ13C and δ18O isotopes, 87Sr/86Sr ratios, and U‐Pb age dating of various dolomite phases. In this example, a Triassic carbonate platform was dissected and overprinted (diagenetic temperatures of 50 to 430°C) in a strike‐slip zone in Southern Spain. Eight episodes of dolomitization, a dolostone cataclasite and late stage meteoric/vadose cementation were recognized. The following processes were found to be diagenetically relevant: (i) protolith deposition and fabric‐preservation, and marine dolomitization of precursor aragonite and calcite during the Middle–Late Triassic; (ii) intermediate burial and formation of zebra saddle dolomite and precipitation of various dolomite cements in a Proto‐Atlantic opening stress regime (T ca 250°C) during the Early–Middle Jurassic; (iii) dolomite cement precipitation during early Alpine tectonism, rapid burial to ca 15 km, and high‐grade anchizone overprint during Alpine tectonic evolution in the Early Eocene to Early Miocene; (iv) brecciation of dolostones to cataclasite during the onset of the Carboneras Fault Zone activity during the Middle Miocene; and (v) late‐stage regression and subsequent meteoric overprint. Data shown here document that, under favourable conditions, early diagenetic marine dolomites and their archive data may resist petrographic and geochemical resetting over time intervals of 108 or more years. Evidence for this preservation includes preserved Late Triassic seawater δ13CDIC values and primary fluid inclusion data. Data also indicate that oversimplified statements based on bulk data from other petrographically‐complex dolomite archives must be considered with caution

Prokaryotic Heme Biosynthesis: Multiple Pathways to a Common Essential Product

The advent of heme during evolution allowed organisms possessing this compound to safely and efficiently carry out a variety of chemical reactions that otherwise were difficult or impossible. While it was long assumed that a single heme biosynthetic pathway existed in nature, over the past decade, it has become clear that there are three distinct pathways among prokaryotes, although all three pathways utilize a common initial core of three enzymes to produce the intermediate uroporphyrinogen III. The most ancient pathway and the only one found in the Archaea converts siroheme to protoheme via an oxygen-independent four-enzyme-step process. Bacteria utilize the initial core pathway but then add one additional common step to produce coproporphyrinogen III. Following this step, Gram-positive organisms oxidize coproporphyrinogen III to coproporphyrin III, insert iron to make coproheme, and finally decarboxylate coproheme to protoheme, whereas Gram-negative bacteria first decarboxylate coproporphyrinogen III to protoporphyrinogen IX and then oxidize this to protoporphyrin IX prior to metal insertion to make protoheme. In order to adapt to oxygen-deficient conditions, two steps in the bacterial pathways have multiple forms to accommodate oxidative reactions in an anaerobic environment. The regulation of these pathways reflects the diversity of bacterial metabolism. This diversity, along with the late recognition that three pathways exist, has significantly slowed advances in this field such that no single organism's heme synthesis pathway regulation is currently completely characterized

Shelf ice-associated cryo-benthos and environmental features

Incidences of cryo-benthic communities beneath ice shelves are rare and recent discoveries. Combined seal- and ROV-borne imagery and novel sampling technologies allowed for a re-assessment and augmentation of earlier findings on a cryo-benthic isopod community (Antarcturus cf. spinacoronatus), being attached head-down to the underside of floating shelf ice at depths of around 80-150m. The shelf ice-associated cryo-benthos was discovered at Drescher Inlet (-72.83667 -19.15300), Riiser-Larsen Ice Shelf (eastern Weddell Sea). The inlet constitutes a 25km long and between 2 and 4km wide crack in the surrounding shelf ice, which is associated with certain environmental features. Here we compile all available local physical, biological, and biogeochemical data and discuss their relevance in the wider regional context for this faunal hotspot. These include data on shelf, sea and platelet ice, seafloor topography, hydrography and water chemistry, as well as associated pelagic and benthic marine life, in particular affinities of the cryo-benthic isopod community to related fauna occurring in nearby seabed communities using molecular barcoding