Description: Euphausiids constitute a major biomass component in shelf ecosystems and play a fundamental role in the rapid vertical transport of carbon from the ocean surface to the deeper layers during their daily vertical migration (DVM). DVM depth and migration patterns depend on oceanographic conditions with respect to temperature, light and oxygen availability at depth, factors that are highly dependent on season in most marine regions. Here we introduce a global krill respiration ANN (artificial neural network) model including the effect of latitude (LAT), the day of the year (DoY), and the number of daylight hours (DLh), in addition to the basal variables that determine ectothermal oxygen consumption (temperature, body mass and depth). The newly implemented parameters link space and time in terms of season and photoperiod to krill respiration. The ANN model showed a better fit (r2 = 0.780) when DLh and LAT were included, indicating a decrease in respiration with increasing LAT and decreasing DLh. We therefore propose DLh as a potential variable to consider when building physiological models for both hemispheres. For single Euphausiid species investigated in a large range of DLh and DoY, we also tested the standard respiration rate for seasonality with Multiple Linear Regression (MLR) and General Additive model (GAM). GAM successfully integrated DLh (r2 = 0.563) and DoY (r2 = 0.572) effects on respiration rates of the Antarctic krill, Euphausia superba, yielding the minimum metabolic activity in mid-June and the maximum at the end of December. We could not detect DLh or DoY effects in the North Pacific krill Euphausia pacifica, and our findings for the North Atlantic krill Meganyctiphanes norvegica remained inconclusive because of insufficient seasonal data coverage. We strongly encourage comparative respiration measurements of worldwide Euphausiid key species at different seasons to improve accuracy in ecosystem modeling.

Description: Euphausiids constitute a major biomass component in shelf ecosystems and play a fundamental role in the rapid vertical transport of carbon from the ocean surface to the deeper layers during their daily vertical migration (DVM). DVM depth and migration patterns depend on oceanographic conditions with respect to temperature, light and oxygen availability at depth, factors that are highly dependent on season in most marine regions. Here we introduce a global krill respiration ANN (Artificial Neural Network) model including the effect of latitude (LAT), the day of the year (DoY), and the number of daylight hours (DLh), in addition to the basal variables that determine ectothermal oxygen consumption (temperature, body mass and depth). The newly implemented parameters link space and time in terms of season and photoperiod to krill respiration. The ANN model showed a better fit (r2=0.780) when DLh and LAT were included, indicating a decrease in respiration with increasing LAT and decreasing DLh. We therefore propose DLh as a potential variable to consider when building physiological models for both hemispheres. For single Euphausiid species investigated in a large range of DLh and DoY, we also tested the standard respiration rate for seasonality with Multiple Linear Regression (MLR) and General Additive model (GAM). GAM successfully integrated DLh (r2= 0.563) and DoY (r2= 0.572) effects on respiration rates of the Antarctic krill, Euphausia superba, yielding the minimum metabolic activity in mid-June and the maximum at the end of December. We could not detect DLh or DoY effects in the North Pacific krill Euphausia pacifica, and our findings for the North Atlantic krill Meganyctiphanes norvegica remained inconclusive because of insufficient seasonal data coverage. We strongly encourage comparative respiration measurements of worldwide Euphausiid key species at different seasons to improve accuracy in ecosystem modelling.

Description: This study shows that macrofaunal irrigation traits constitute a valuable complement to sediment reworking traits in estimating macrofaunal impact on nutrient fluxes across the sediment-water interface. We correlated density, biomass, community bioturbation potential (BPc, an index based on reworking traits, body mass and density) and community irrigation potential (IPc, an index based on irrigation traits, body mass and density) with nitrite, nitrate, ammonium, silicate and phosphate flux data under different environmental conditions. Generalized linear models performed best with a combination of environmental conditions and irrigation trait-based indices. This was not only a direct effect of the irrigation traits, but also of the scaling factor 0.75 employed in IPc to infer metabolic activity from body mass. Accordingly, predictive models of nutrient flux across the sediment-water interface will profit greatly from incorporating macrofaunal irrigation behaviour by means of trait-based indices.

Description: Growth, mortality and productivity of the hard clam E. exalbida from Ushuaia Bay, Beagle Channel were investigated. The parameters of the von Bertalanffy growth function were estimated to be H = 73.98 mm, K = 0.180 y 1, t0 = 0.147 y. Maximum individual production amounted to 2.742 g shell free wet mass (SFWM) at 49.5 mm shell height. Animals between 40 mm and 70 mm shell height contribute most to overall population somatic production P of 133.89 g SFWM m-2 y-1. Mean annual biomass B amounted to 1122.69 g SFWM m-2 y-1. Annual P/B ratio and mortality rate Z were estimated to 0.119 y-1 and 0.141 y-1, respectively. Slow growth and low turnover makes this population less suitable for sustainable commercial exploitation.

Description: The trophic structure of the German Bight soft-bottom benthic community was evaluated for potential changes after cessation of bottom trawling. Species were collected with van-Veen grabs and beam trawls. Trophic position (i.e. nitrogen stable isotope ratios, δ15N) and energy flow (i.e. species metabolism approximated by body mass scaled abundance) of dominant species were compared in trawled areas and an area protected from fisheries for 14 months in order to detect trawling cessation effects by trophic characteristics. At the community level, energy flow was lower in the protected area, but we were unable to detect significant changes in trophic position. At the species level energy flow in the protected area was lower for predating/scavenging species but higher for interface feeders. Species trophic positions of small predators/scavengers were lower and of deposit feeders higher in the protected area. Major reasons for trophic changes after trawling cessation may be the absence of artificial and additional food sources from trawling likely to attract predators and scavengers, and the absence of physical sediment disturbance impacting settlement/survival of less mobile species and causing a gradual shift in food availability and quality. Our results provide evidence that species or community energy flow is a good indicator to detect trawling induced energy-flow alterations in the benthic system, and that in particular species trophic properties are suitable to capture subtle and short-term changes in the benthos following trawling cessation.

Description: We compared primary production and respiration of temperate (Helgoland, North Sea) and subtidal Arctic (Kongsfjorden, Svalbard) microphytobenthic communities during summer. The diatom communities were generally characterized as cosmopolitan, displayed no site specificity, and had similar chl a and fucoxanthin concentrations. Their net and gross photosynthesis rates and light adaptation intensities, derived from laboratory microsensor measurements, were also similar, despite differences in water temperature. Daily oxygen fluxes across the sediment− water interface were estimated by combining laboratory microprofile and planar optode measurements with in situ data on oxygen penetration and light dynamics. During the study period, the Svalbard sediments were on average net heterotrophic,while the Helgoland sediments were net autotrophic (−22.4 vs. 9.2 mmol O2 m−2 d−1). This was due to high infaunal abundance in the Svalbard sediments that caused high oxygen uptake rates in the sediments and consumption below the sediment euphotic zone. Additionally, bioirrigation of the sediment due to infaunal burrow ventilation was reduced by light; thus, the sedimentary oxygen inventory was reduced with increasing light. Conversely, light-enhanced the oxygen inventory in the Helgoland sediments. Oxygen dynamics in the Svalbard sediments were therefore dominated by bioirrigation, whereas in the Helgoland sediments they were dominated by photosynthetic oxygen production.

Description: Macrofaunal sediment reworking activity is a key driver of ecosystem functioning in marine systems. So far sediment reworking rates can only accurately be assessed by measurements as inference from community parameters is limited. In this case study we test the applicability of 2-D optical florescent sediment profile imaging (f-SPI) on multi corer type incubation cylinders. f-SPI has to date been applied to flat-surfaced (i.e. rectangular) cores only, while multi corer type incubation cylinders were analyzed by the spatially low resolved and invasive slicing technique. Here we apply both methods to cylindrical sediment cores (10 cm diameter). Cores were taken from by two common communities (i.e. Nucula-community and Amphiura-community) in the southern German Bight. Both f-SPI and the slicing technique showed similar vertical luminophore profiles. However the slicing technique found no significant differences between the two communities, whereas f-SPI showed significant differences for all investigated sediment reworking parameters: sediment reworking rate, non-locality index, mean weighted luminophore depth, and the maximal luminophore depth. Consequently, this may lead to different conclusions about the sediment reworking behaviors of the two communities. Likely the slicing method failed to detect significant differences between the Nucula- and Amphiura-community, owing to insufficient spatial accuracy. The f-SPI method, on the other hand, did not capture the full extent of maximal sediment reworking depth due to wall-effects. We conclude that both methods have specific drawbacks and advantages. While slicing is preferable when focusing on the absolute maximal sediment reworking depth especially with predominantly sessile communities, f-SPI is better suited to capture general sediment reworking patterns of most other communities. We demonstrate further that the bias, which is introduced by the distortion effect on imaging due to optical perspective and cylinder wall curvature of rounded cylinders using f-SPI, is negligible. Accordingly our results indicate that the distortion effects by curvature of the rounded cylinder walls will not cause underestimations of sediment reworking parameters in the f-SPI approach. Consequently f-SPI is suitable for the investigation of sediment reworking in natural communities by means of multi corer type samples.

Description: Understanding past seasonal temperature variability in the ocean is essential to evaluate the effects of future climate change on marine ecosystems. Here, we estimate seasonal water temperature amplitudes from stable oxygen isotope (δ18Oshell) values of fossil shells of Arctica islandica (assuming δ18Owater = + 0.9 ± 0.1‰ V-SMOW). Specimens were collected from three Pleistocene successions (Emilian and Sicilian substages of the Calabrian) in Central and Southern Italy (i.e., Rome, Lecce and Sicily). Biostratigraphic analyses from Rome Quarry deposits indicate an age between 1.6 and 1.2 Ma, whereas Sicily and Lecce successions are slightly more recent (between 1.1 and 0.62 Ma). Prior to carbonate geochemical analysis, we checked the shells for potential diagenetic alterations (e.g., from aragonite to calcite) using confocal Raman microscopy. δ18Oshell transects indicate an annual temperature amplitude of about 3 °C during the Early Pleistocene. This is in sharp contrast to reconstructions based on faunal assemblages, according to which the simultaneous occurrence of boreal and warm-water species in the Calabrian Mediterranean Sea suggests a much higher seasonality (ca. 10 °C). The low seasonality and the relatively cold water (9–10 °C) indicate the outcrops represent colder climatic conditions compared to modern times, and suggest the occurrence of a maximum glacial phase.