CellTracker Green labelling vs. rose bengal staining : CTG wins by points in distinguishing living from dead anoxia-impacted copepods and nematodes

Hypoxia and anoxia have become a key threat to shallow coastal seas. Much is known about their impact on macrofauna, less on meiofauna. In an attempt to shed more light on the latter group, in particular from a process-oriented view, we experimentally induced short-term anoxia (1 week) in the northern Adriatic Sea (Mediterranean) and examined the two most abundant meiofauna taxa - harpacticoid copepods and nematodes. Both taxa also represent different ends of the tolerance spectrum, with copepods being the most sensitive and nematodes among the most tolerant. We compared two methods: CellTracker Green (CTG) - new labelling approach for meiofauna - with the traditional rose bengal (RB) staining method. CTG binds to active enzymes and therefore colours live organisms only. The two methods show considerable differences in the number of living and dead individuals of both meiofauna taxa. Generally, RB will stain dead but not yet decomposed copepods and nematodes equally as it does live ones. Specifically, RB significantly overestimated the number of living copepods in all sediment layers in anoxic samples, but not in any normoxic samples. In contrast, for nematodes, the methods did not show such a clear difference between anoxia and normoxia. RB overestimated the number of living nematodes in the top sediment layer of normoxic samples, which implies an overestimation of the overall live nematofauna. For monitoring and biodiversity studies, the RB method might be sufficient, but for more precise quantification of community degradation, especially after an oxygen depletion event, CTG labelling is a better tool. Moreover, it clearly highlights the surviving species within the copepod or nematode community. As already accepted for foraminiferal research, we demonstrate that the CTG labelling is also valid for other meiofauna groups

Meiofauna winners and losers of coastal hypoxia : case study harpacticoid copepods

The impact of anoxia on meiobenthic copepod species was assessed by means of a field experiment. Four plexiglass chambers were deployed in situ in 24 m depth to simulate an anoxic event of 9 days, 1 month, 2 months and 10 months. From normoxic to anoxic conditions, we recorded a drop in copepod density and species richness. With increasing duration of anoxia the relative abundance of the individuals of the family Cletodidae increased, and they survived the 1 month and 2 month anoxia, the latter with few specimens. They were the true "winners" of the experimentally induced anoxia. Dominance did not increase in the deployments because not one, but several species from this family were tolerant to anoxia. The overall rate of survival was the same for males and females, but no juvenile stages of copepods survived in anoxia. During a recovery phase of 7 days after a short-term anoxia of 9 days, harpacticoid copepod density did not increase significantly, and there was only a slight increase in species diversity. We concluded that no substantial colonisation from the surrounding sediment took place. The survivors, however, showed a high potential for recovery according to the number of gravid females, whose number increased significantly once the oxygen was available again. These findings imply that substantial energy is allocated to reproduction in the recovery phase

PESCO als "Game Changer": zur sicherheitspolitischen Akteursfähigkeit der EU und Österreichs Beitrag

Das neue Instrument der Gemeinsamen Sicherheits- und Verteidigungspolitik (GSVP) der Europäischen Union (EU) PESCO entwickelt sich kontinuierlich. Hier schließen sich EU-Mitgliedstaaten zusammen, um im Rahmen von Projekten ihre militärischen Fähigkeiten und Kapazitäten schrittweise zu verbessern. Dabei handelt es sich ebenso wenig um zahnlose Willensbekundungen wie um eine reine Militarisierung der EU, sondern um die Entwicklung konkreter verteidigungsrelevanter Kapazitäten. Wichtige Erfolgsfaktoren dafür sind die Verknüpfung mit den Strukturen und Institutionen der GSVP und die Kombination aus intergouvernmentaler Arbeitsweise auf Ratsebene und Flexibilität und Freiwilligkeit auf Projektebene. PESCO wird dadurch zum echten Game Changer im Bereich EU-Verteidigungskooperation. In diesem Arbeitspapier wird anhand des "Actorness"-Ansatzes von Charlotte Bretherton und John Vogler (2006) überprüft, inwiefern sich die EU als Sicherheitsakteur durch PESCO weiterentwickelt und wie Österreich in diesem Prozess positioniert ist. Insgesamt zeigt die Analyse, dass PESCO die vier Kriterien der Capability-Kategorie des Actorness-Konzeptes erfüllt: Bekenntnis zu gemeinsamen Grundwerten, Kontinuität und Legitimität durch die teilnehmenden Mitgliedstaaten und die nationalen Bevölkerungen, Fähigkeit zur Identifizierung von Prioritäten und Umsetzung von policies und Richtlinien, Verfügbarkeit und Nutzung militärischer Instrumente. Deshalb kann die EU durch PESCO als ein Sicherheitsakteur im Wachsen begriffen werden, der sich eindeutig weiterentwickelt. Österreichs Engagement war hier bisher professionell und verlässlich. Die Implementierung bisheriger Projekte, insbesondere des von Österreich geleiteten CBRN SaaS, sollten Priorität haben. Die Möglichkeit für Beobachterstatus bei Flaggschiff-Projekten sollte geprüft werden

Effect of hypoxia and anoxia on invertebrate behaviour: Ecological perspectives from species to community level

Coastal hypoxia and anoxia have become a global key stressor to marine ecosystems, with almost 500 dead zones recorded worldwide. By triggering cascading effects from the individual organism to the community-and ecosystem level, oxygen depletions threaten marine biodiversity and can alter ecosystem structure and function. By integrating both physiological function and ecological processes, animal behaviour is ideal for assessing the stress state of benthic macrofauna to low dissolved oxygen. The initial response of organisms can serve as an early warning signal, while the successive behavioural reactions of key species indicate hypoxia levels and help assess community degradation. Here we document the behavioural responses of a representative spectrum of benthic macrofauna in the natural setting in the Northern Adriatic Sea (Mediterranean). We experimentally induced small-scale anoxia with a benthic chamber in 24 m depth to overcome the difficulties in predicting the onset of hypoxia, which often hinders full documentation in the field. The behavioural reactions were documented with a time-lapse camera. Oxygen depletion elicited significant and repeatable changes in general (visibility, locomotion, body movement and posture, location) and species-specific reactions in virtually all organisms (302 individuals from 32 species and 2 species groups). Most atypical (stress) behaviours were associated with specific oxygen thresholds: arm-tipping in the ophiuroid Ophiothrix quinquemaculata, for example, with the onset of mild hypoxia (< 2 mL O2 L-1), the emergence of polychaetes on the sediment surface with moderate hypoxia (< 1 mL O 2 L-1), the emergence of the infaunal sea urchin Schizaster canaliferus on the sediment with severe hypoxia (< 0.5 mL O 2 Lg-1) and heavy body rotations in sea anemones with anoxia. Other species changed their activity patterns, for example the circadian rhythm in the hermit crab Paguristes eremita or the bioherm-associated crab Pisidia longimana. Intra-and interspecific reactions were weakened or changed: decapods ceased defensive and territorial behaviour, and predator-prey interactions and relationships shifted. This nuanced scale of resolution is a useful tool to interpret present benthic community status (behaviour) and past mortalities (community composition, e.g. survival of tolerant species). This information on the sensitivity (onset of stress response), tolerance (mortality, survival), and characteristics (i.e. life habit, functional role) of key species also helps predict potential future changes in benthic structure and ecosystem functioning. This integrated approach can transport complex ecological processes to the public and decision-makers and help define specific monitoring, assessment and conservation plans. © 2014 Author (s).This study was financed by the Austrian Science Fund (FWF; projects P17655-B03 and P21542-B17) and supported by the OEAD Bilateral Slovenian Austrian Scientific Technical Cooperation project SI 22/2009Peer Reviewe

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Hermit crabs and their symbionts: Reactions to artificially induced anoxia on a sublittoral sediment bottom

Hermit crabs play an important role in the Northern Adriatic Sea due to their abundance, wide range of symbionts, and function in structuring the benthic community. Small-scale (0.25 m2) hypoxia and anoxia were experimentally generated on a sublittoral soft bottom in 24 m depth in the Gulf of Trieste. This approach successfully simulates the seasonal low dissolved oxygen (DO) events here and enabled studying the behaviour and mortality of the hermit crab Paguristes eremita. The crabs exhibited a sequence of predictable stress responses and ultimately mortality, which was correlated with five oxygen thresholds. Among the crustaceans, which are a sensitive group to oxygen depletion, P. eremita is relatively tolerant. Initially, at mild hypoxia (2.0 to 1.0 ml l− 1 DO), hermit crabs showed avoidance by moving onto better oxygenated, elevated substrata. This was accompanied by a series of responses including decreased locomotory activity, increased body movements and extension from the shell. During a moribund phase at severe hypoxia (0.5 to 0.01 ml l− 1 DO), crabs were mostly immobile in overturned shells and body movements decreased. Anoxia triggered emergence from the shell, with a brief locomotion spurt of shell-less crabs. The activity pattern of normally day-active crabs was altered during hypoxia and anoxia. Atypical interspecific interactions occurred: the crab Pisidia longimana increasingly aggregated on hermit crab shells, and a hermit crab used the emerged infaunal sea urchin Schizaster canaliferus as an elevated substrate. Response patterns varied somewhat according to shell size or symbiont type (the sponge Suberites domuncula). Mortality occurred after extended anoxia (~ 1.5 d) and increased hydrogen sulphide levels (H2S ~ 128 μmol). The relative tolerance of crabs and certain symbionts (e.g. the sea anemone Calliactis parasitica) – as potential survivors and recolonizers of affected areas – may influence and promote community recovery after oxygen crises