Description: Background Reactive oxygen (ROS) and nitrogen (RNS) species are produced during normal unstressed metabolic activity in aerobic tissues. Most analytical work uses tissue homogenates, and lacks spatial information on the tissue specific sites of actual ROS formation. Live-imaging techniques (LIT) utilize target-specific fluorescent dyes to visualize biochemical processes at cellular level. Results Together with oxidative stress measurements, here we report application of LIT to bivalve gills for ex-vivo analysis of gill physiology and mapping of ROS and RNS formation in the living tissue. Our results indicate that a) mitochondria located in the basal parts of the epithelial cells close to the blood vessels are hyperpolarized with high Δψm, whereas b) the peripheral mitochondria close to the cilia have low (depolarized) Δψm. These mitochondria are densely packed (mitotracker Deep Red 633 staining), have acidic pH (Ageladine-A) and collocate with high formation of nitric oxide (DAF-2DA staining). NO formation is also observed in the endothelial cells surrounding the filament blood sinus. ROS (namely H2O2, HOO• and ONOO− radicals, assessed through C-H2DFFDA staining) are mainly formed within the blood sinus of the filaments and are likely to be produced by hemocytes as defense against invading pathogens. On the ventral bend of the gills, subepithelial mucus glands contain large mucous vacuoles showing higher fluorescence intensities for O2 •- than the rest of the tissue. Whether this O2 •- production is instrumental to mucus formation or serves antimicrobial protection of the gill surface is unknown. Cells of the ventral bends contain the superoxide forming mucocytes and show significantly higher protein carbonyl formation than the rest of the gill tissue. Conclusions In summary, ROS and RNS formation is highly compartmentalized in bivalve gills under unstressed conditions. The main mechanisms are the differentiation of mitochondria membrane potential and basal ROS formation in inner and outer filament layers, as well as potentially antimicrobial ROS formation in the central blood vessel. Our results provide new insight into this subject and highlight the fact that studying ROS formation in tissue homogenates may not be adequate to understand the underlying mechanism in complex tissues.

Description: Background: Scavenger guilds, composed of a variety of species, co-existing in the same habitat, are responsible for biomass transformation throughout the food web. Niche partitioning among them can manifest in different feeding strategies, e.g. during carcass feeding. In the bentho-pelagic realm of the Southern Ocean, scavenging amphipods of the speciose superfamily Lysianassoidea are amongst the ubiquitous taxa and occupy an essential role in decomposition processes. First, we addressed the question whether scavenging lysianassoid amphipods have different feeding strategies during carcass feeding, and if their potential synergistic feeding activities influence carcass decomposition. To this end, we compared the relatively large-sized species Waldeckia obesa with the small-sized species Cheirimedon femoratus, Hippomedon kergueleni, and Orchomenella rotundifrons during carcass feeding (Notothenia spp.). Our approach combines ex situ feeding experiments, behavioural observations, and scanning electron microscopic analyses of mandibles. Secondly, we aimed to detect ecological drivers for succession patterns of scavenging amphipods in Antarctic coastal ecosystems affected by environmental disturbances. In Potter Cove, the climate-driven rapid retreat of the Fourcade Glacier is causing various environmental changes including the provision of new marine habitats to colonise. While in the newly ice-free areas fish records are rare, macroalgae have already colonised hard substrates. Therefore, we carried out feeding assays of the most abundant lysianassoids in Potter Cove C. femoratus and H. kergueleni, to determine their consumption rates (mg food x mg amphipods-1 x day-1) and preferences of macroalgae and fish. Results We detected two functional groups with different feeding strategies among the investigated scavenging amphipods: the 'outside-insider' (openers) and 'inside-outsider' (squeezers). Synergistic effects during carcass feeding was not statistical evident. C. femoratus showed a flexible diet when fish was not available by consuming macroalgae with a consumption about 0.2 day-1 but preferred fish with feedings rates up to 0.8 day-1. Contrary, H. kergueleni rejected macroalgae entirely and consumed fish with consumption rates up to 0.8 day-1. Conclusion This study reveals functional groups in scavenging shallow water amphipods and provides new information on coastal intraguild niche partitioning. Moreover, we conclude that dietary flexibility of scavenging amphipods is a potential ecological driver for succession and colonisation of newly available ice-free Antarctic coastal habitats.

Description: The west Antarctic Peninsula (WAP) region has undergone significant changes in temperature and seasonal ice dynamics since the mid-twentieth century, with strong impacts on the regional ecosystem, ocean chemistry and hydrographic properties. Changes to these long-term trends of warming and sea ice decline have been observed in the 21st century, but their consequences for ocean physics, chemistry and the ecology of the high-productivity shelf ecosystem are yet to be fully established. The WAP shelf is important for regional krill stocks and higher trophic levels, whilst the degree of variability and change in the physical environment and documented biological and biogeochemical responses make this a model system for how climate and sea ice changes might restructure high-latitude ecosystems. Although this region is arguably the best-measured and best-understood shelf region around Antarctica, significant gaps remain in spatial and temporal data capable of resolving the atmosphere-ice-ocean-ecosystem feedbacks that control the dynamics and evolution of this complex polar system. Here we summarise the current state of knowledge regarding the key mechanisms and interactions regulating the physical, biogeochemical and biological processes at work, the ways in which the shelf environment is changing, and the ecosystem response to the changes underway. We outline the overarching cross-disciplinary priorities for future research, as well as the most important discipline-specific objectives. Underpinning these priorities and objectives is the need to better-define the causes, magnitude and timescales of variability and change at all levels of the system. A combination of traditional and innovative approaches will be critical to addressing these priorities and developing a co-ordinated observing system for the WAP shelf, which is required to detect and elucidate change into the future.

Description: Iron stable isotope signatures (δ56Fe) in hemolymph (bivalve blood) of the Antarctic bivalve Laternula elliptica were analyzed by Multiple Collector - Inductively Coupled Plasma - Mass Spectrometry (MC-ICP-MS) to test whether the isotopic fingerprint can be tracked back to the predominant sources of the assimilated Fe. An earlier investigation of Fe concentrations in L. elliptica hemolymph suggested that an assimilation of reactive and bioavailable Fe (oxyhydr)oxide particles (i.e. ferrihydrite), precipitated from pore water Fe around the benthic boundary, is responsible for the high Fe concentration in L. elliptica (Poigner et al., 2013b). At two stations in Potter Cove (King George Island, Antarctica) bivalve hemolymph showed mean δ56Fe values of −1.19 ± 0.34‰ and -1.04 ± 0.39‰, respectively, which is between 0.5‰ and 0.85‰ lighter than the pool of easily reducible Fe (oxyhydr)oxides of the surface sediments (−0.3‰ to −0.6‰). This is in agreement with the enrichment of lighter Fe isotopes at higher trophic levels, resulting from the preferential assimilation of light isotopes from nutrition. Nevertheless, δ56Fe hemolymph values from both stations showed a high variability, ranging between −0.21‰ (value close to unaltered/primary Fe(oxyhydr)oxide minerals) and −1.91‰ (typical for pore water Fe or diagenetic Fe precipitates), which we interpret as a “mixed” δ56Fe signature caused by Fe assimilation from different sources with varying Fe contents and δ56Fe values. Furthermore, mass dependent Fe fractionation related to physiological processes within the bivalve cannot be ruled out. This is the first study addressing the potential of Fe isotopes for tracing back food sources of bivalves.