A time-lapse camera experiment on benthic reactions to anoxia in the Northern Adriatic Sea

Hypoxie und Anoxie sind Schlüsselfaktoren, welche die heutigen flachen Küstenökosysteme weltweit bedrohen. Das Auftreten von Sauerstoffarmut hat in den letzten Jahrzehnten sowohl in der Häufigkeit als auch in der Intensität stark zugenommen. In der Adria können bis zu 3000 km² des Meeresgrundes von Hypoxie betroffen sein, was zu ausgedehnten Massensterben des Benthos führt. Der Beginn solcher Katastrophen ist kaum vorherzusagen. Mit Hilfe eines Gerätes, das experimentell Anoxie erzeugt, dokumentierten wir in der nördlichen Adria in 24 m Tiefe eine Sauerstoffkrise in kleinem Maßstab (0.25 m²). Das Gerät kombiniert fotografische Dokumentation mit detaillierter chemo-physikalischer Messung und ermöglicht Verhaltens- und Mortalitätsanalysen der benthischen Organismen vor, während und nach der Sauerstoffarmut. Die Reaktionen auf den abnehmenden Sauerstoffgehalt und/oder die ansteigende Dauer der Anoxie waren: (1) vermehrte oder verminderte Aktivität, (2) Auftreten von atypischem Verhalten, (3) unerwartete intraspezifische Interaktionen, (4) Hervorkommen von Infauna und (5) Mortalität. Die Verhaltensweisen und Sterberaten der ausgewählten Arten wurden mit fünf Sauerstoffkategorien in Korrelation gesetzt: normale Sauerstoffkonzentration (>2.0 ml O2 l-1), leichte (≤2.0-1.01 ml O2 l-1), moderate (1.0-0.51 ml O2 l-1) und ernste Hypoxie (0.5-0.01 ml O2 l-1) und Anoxie. Die Ergebnisse zeigten große Unterschiede zwischen den ausgewählten Arten im Bezug auf die Hypoxie- bzw. Anoxietoleranz. Leichte Hypoxie, zum Beispiel, löste eine erhöhte Lokomotionsaktivität des Schlangensterns Ophiothrix quinquemaculata und des Gastropoden Hexaplex trunculus aus, was als Fluchtverhalten gedeutet wird. Zudem wurden verschiedene artspezifische subletale Reaktionen dokumentiert, wie etwa die Körperausdehnung bei der Seeanemone Cereus pedunculatus und der Seegurke Ocnus planci oder die Mantelschwellung bei der epifaunalen Bivalve Chlamys varia. Moderate Hypoxie forcierte das Hervorkommen des infaunalen Seeigels Schizaster canaliferus. Bei ernster Hypoxie begannen die Seescheiden ihre Siphonen zu schließen und die Aktivität der Schlangensterne sank deutlich, bis sie letztendlich starben. Bei Anoxie wurden die ersten Mortalitäten dokumentiert, unter anderem die Schlangensterne, infaunale Seeigel und C. varia; C. pedunculatus, H. trunculus und die infaunale Bivalve Corbula gibba überlebten. Die vorliegende Studie, in Kombination mit laufenden Experimenten, ist ein wichtiger Schritt, um einen allgemein gültigen Katalog von Verhaltensreaktionen und eine Liste von empfindlichen und toleranten Arten erstellen zu können. Dieses Herangehen wird letztendlich dazu beitragen, den Status benthischer Ökosysteme, welche einer Sauerstoffarmut ausgesetzt sind, besser einzuschätzen.Hypoxia and anoxia are key threats to modern shallow coastal ecosystems worldwide. The occurrence of oxygen depletion events has increased dramatically over recent decades both in frequency and intensity. In the Adriatic Sea, hypoxia may affect up to 3000 km² of the seafloor, leading to extensive mass mortalities of the benthos. The onset of these catastrophic events, however, is hard to predict. Deploying an experimental anoxia generating unit (EAGU) we created and fully documented a small-scale anoxia event (0.25 m2) in 24 m depth, in the northern Adriatic Sea. The instrument combines photo-documentation with detailed chemo-physical recording and allows the analysis of the behaviors and mortalities of benthic organisms before, during and after oxygen depletion. The responses to declining oxygen values and/or to increasing duration of anoxia were: (1) increase or decrease in normal activities, (2) initiation of atypical behaviors, (3) unexpected intraspecific interactions, (4) emergence of infauna, and (5) mortalities. The documented behaviors and mortalities of the selected species were correlated to five oxygen categories: normoxia (>2.0 ml O2 l-1), weak hypoxia (≤2.0-1.01 ml O2 l-1), moderate (1.0-0.51 ml O2 l-1) and severe hypoxia (0.5-0.01 ml O2 l-1) and anoxia. The results show considerable differences in tolerance to oxygen depletion from species to species. Weak hypoxia triggered increased locomotion in the brittle star Ophiothrix quinquemaculata and in the gastropod Hexaplex trunculus, which is interpreted as an escape behavior. Different species-specific sublethal responses were observed, such as body extension in the sea anemone Cereus pedunculatus, and in the sea cucumber Ocnus planci, or swollen mantle tissue in the epifaunal bivalve Chlamys varia. Moderate hypoxia elicited the emergence of the infaunal sea urchin Schizaster canaliferus. At severe hypoxia ascidians began to close their siphon and the activity of the ophiuroids ceased followed by a moribund phase. The first mortalities occurred at the onset of anoxia. The brittle stars, infaunal sea urchins and C. varia were among the first to die; C. pedunculatus, H. trunculus, the infaunal bivalve Corbula gibba survived. The present study, together with ongoing experiments, is an important step in compiling a generally valid catalogue of reactions and a list of sensitive and tolerant species. This approach will ultimately help to better determine the status of benthic ecosystems exposed to oxygen depletion here and elsewhere

Recent planktic foraminifera in the Fram Strait: ecology and biogeochemistry

This study describes the ecology (species abundances, depth habitat), the stable isotope compostion (carbon and oxygen isotopes) and the Mg/Ca ratios of recent planktic foraminifera in the Fram Strait

Oxygen and carbon isotope composition of modern planktic foraminifera and near-surface waters in the Fram Strait (Arctic Ocean) – a case-study

The upper 500 m of the water column and the sediment surface along an E–W transect in the Fram Strait were sampled for recent planktic foraminifera. The δ18O and δ13C values of the tests are compared to the stable isotope composition of water samples taken from the same depths, and related to the characteristics of the water column. The polar species Neogloboquadrina pachyderma (sin.) clearly dominates the species assemblage in the Fram Strait in the early summer, while the subpolar Turborotalita quinqueloba accounts only for 5–23%. In this area the average depth of calcification of N. pachyderma (sin.) lies between 70–150m water depth, T. quinqueloba shows a similar range with 50–120 m water depth. The δ18O values of N. pachyderma (sin.) show an average vital effect of about −1.5‰ compared to calculated equilibrium calcite values. Except for the upper ~ 75 m, the vertical profiles of δ13C of the net-sampled shells are nearly parallel to the values measured in the water column with an average offset of −1.6‰ and −3.6‰ for N. pachyderma (sin.) and T. quinqueloba, respectively. The discrepancy found in the upper ~ 75 m might indicate the influence of the "carbonate ion effect" on the carbon isotope incorporation in the tests. Oxygen and carbon isotopes from the sediment surface yield higher values than those from the water column for both species. This may be because specimens from the water column reflect a modern snapshot only, while tests from surface sediments record environmental parameters from the past ~ 1000 years

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

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 24m 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 (< 2mLO(2) L-1), the emergence of polychaetes on the sediment surface with moderate hypoxia (< 1mLO(2) L-1), the emergence of the infaunal sea urchin Schizaster canaliferus on the sediment with severe hypoxia (< 0.5mLO(2) L-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 plan

Species distribution and depth habitat of recent planktic foraminifera in Fram Strait, Arctic Ocean

To describe the horizontal and vertical distribution of recent planktic foraminifera in Fram Strait (Arctic), plankton samples were collected in the early summer of 2011 using a MultiNet sampler (&gt;63 µm) at 10 stations along a west–east transect at 78°50′N. Five depth intervals were sampled from the sea surface down to 500 m. Additionally, sediment surface samples from the same locations were analysed. The ratio between absolute abundances of planktic foraminifera in the open ocean, at the ice margin and in the ice-covered ocean was found to be approximately 2:4:1. The assemblage was dominated by the polar Neogloboquadrina pachyderma (sin.) and the subpolar Turborotalita quinqueloba, which accounted for 76 and 15% of all tests in the warm, saline Atlantic waters and 90 and 5% in the cold and fresh Polar waters, respectively. Both species had maximum absolute abundances between 0 and 100 m water depth, however, they apparently lived shallower under the ice cover than under ice-free conditions. This indicates that the depth habitat of planktic foraminifera in the study area is predominantly controlled by food availability and not by temperature. The distribution pattern obtained by plankton tows was clearly reflected on the sediment surface and we conclude that the assemblage on the sediment surface can be used as an indicator for modern planktic foraminiferal fauna.Keywords: Planktic foraminifera; Fram Strait; Arctic Ocean; depth habitat; N. pachyderma (sin.); T. quinqueloba.(Published: 27 May 2014)To access the supplementary material for this article, please see Supplementary files in the column to the right (under Article Tools).Citation: Polar Research 2014, 33, 22483, http://dx.doi.org/10.3402/polar.v33.2248