A long-term view on recent changes in abundance of common skate complex in the North Sea

Following decades of declines, populations of large fish recently started to increase in the North Sea, presumably due to reduced fishing pressure. However, population recovery may be too readily claimed, since standardised sampling of fish stocks commenced only in the 1970s, well after many species had already collapsed. A true recovery must be seen from a long-term perspective. The critically endangered common skate (Dipturus batis, Rajidae) species-complex is an example of a large-bodied fish that mostly disappeared before standardised monitoring took place. Here we put the recent increase in population size into a 120-year perspective, throughout three geographical divisions in the North Sea. We analysed a large range of mostly undisclosed historical data and contemporary sources. A reconstruction of Dutch commercial landings data confirms that the species used to be very abundant between 1902 ? 1920, and shows how it steadily declined from 1920 onwards until it got extirpated around 1970. Based on a quantitative analysis of standardized catch numbers from fishery-independent surveys time we conclude that the current abundance of the species is still below historical baselines and represents a local recovery at most. We further demonstrate a prominent and consistent pattern in size-distribution, with larger (mature) individuals only occurring in the northern North Sea. A large dataset on historical stomach contents from the central North Sea confirmed the diet of young common skate, which consisted predominantly of shrimps. Our review exemplifies the importance of marine historical ecology to deduce the natural richness of the North Sea

Supplementary data

For nanoSIMS measurements of R. mucilaginosa cells, we analyzed three sample sets: (i) the original inoculum (Control), (ii) after incubation with 13C-labelled polyethylene without and (iii) with UV-treatment. We measured a total of 1144 regions of interest (ROIs, i.e., corresponding to 1144 individual cells). For IRMS and GCMS measurements we measured 3 replicates for the development of ?13C-CO2 values and CO2 concentration in incubations with R. mucilaginosa (RM) and with 13C-polyethylene (PE), with prior UV-treatment (+UV) and without (-UV) as the sole carbon source as well as in incubations with UV-treated 13C-polyethylene (PE) without R. mucilaginosa

Supplementary data

NanoSIMS measurements of R. mucilaginosa cells, where we analyzed three sample sets: (i) the original inoculum, (ii) after incubation with 13C-labelled polyethylene without and (iii) with UV-treatment. We measured a total of 1144 regions of interest (ROIs, i.e., corresponding to 1144 individual cells) Development of ?13C-CO2 values in incubations with R. mucilaginosa (RM) and with 13C-polyethylene (PE), with prior UV-treatment (+UV) and without (-UV) as the sole carbon source as well as in incubations without R. mucilaginosa

Data from: Prey ingestion rates revealed by back-mounted accelerometers in Eurasian spoonbills

Background Quantifying foraging success in space and time and among individuals is essential for answering many ecological questions and may guide conservation efforts. However, collecting this information is challenging for species that forage on mobile prey and are difficult to observe visually, for example, because they forage in inaccessible areas or at night. In such cases, the use of tracking devices that simultaneously collect location and acceleration data may provide a solution if foraging success can be extracted successfully. The aim of this study was to assess how well searching for and ingesting prey, among other behaviours, could be distinguished from 20 Hz acceleration data collected by GPS/ACC-trackers mounted on the back of Eurasian spoonbills Platalea leucorodia. Upon capturing a prey, spoonbills make a distinct movement with their head and back to throw the prey from the tip of the bill into the throat. Methods We compared the behavioural classification performance of random forest models that were trained and tested on video-annotated acceleration data segments of different (fixed or flexible) lengths. The best-performing model was then applied to 4 years of data of spoonbills foraging in the Wadden Sea during the breeding season, to explore seasonal and annual variation in prey ingestion rates. Results Highest classification accuracies (as indicated by the F-measure, a balanced measure of precision and sensitivity) of foraging behaviours were achieved by analysing short fixed-length segments (0.4-0.8 s) or 'flexibly-cut' segments. The F-measure was very high (> 0.90) for searching, standing, sitting and flying (distinguishing active and passive flight), 0.73 for ingesting prey and 0.65 for walking. False positive and negative prey ingestions were equally likely and most often confused with searching, resulting in a close match between the predicted and observed prey ingestion rates. Application of the best-performing model revealed strong seasonal patterns in prey ingestion rates in the Wadden Sea that varied between years. Conclusions We show that prey ingestion rates of Eurasian spoonbills can be fairly accurately estimated from acceleration data. These results are promising for the use of spoonbills equipped with GPS/ACC-trackers as monitors of spatial and temporal variation in the availability of small fish and shrimp, which is key to understand their foraging and migratory movements of spoonbills and provides information on the quality of (coastal) wetlands

Food web interactions of breeding Arctic shorebirds are shaped by their elevational distribution: dataset

We describe the spatial position of little stints and red knots in the tundra food web, from both a top-down and a bottom-up perspective, and suggest that these affect shorebird diet and survival. The availability of the key food items for chicks is related to their diet, and, although it is not possible to fully disentangle cause and effect, we find support that the diet differences are explained by elevation. Moreover, the difference in the elevational distribution of shorebird nests impacts their relationships with predators

EMIR II - Southern North Sea porewater nutrients

Sediment pore water nutrients from coarse grained, southern North Sea sediments (2019-03-15)

Evaluation of the distributions of hydroxylated isoprenoidal GDGTs in Holocene Baltic Sea sediments for reconstruction of sea surface temperature: The effect of changing salinity

Hydroxylated glycerol dibiphytanyl glycerol tetraethers (OH-GDGTs) produced by both marine and freshwater thaumarchaea are increasingly used for the reconstruction of past sea surface temperature (SST). They occur throughout the modern Baltic Sea, but it is unknown if their OH-GDGTs can be used for assessing past SST in this area, where salinity has changed considerably over the Holocene. Three commonly applied OH-GDGT proxies for SST reconstruction, i.e., the OH-GDGT%, RI-OH, and RI-OH? indices, were tested using a Thaumarchaeotal culture enriched from the Baltic Sea grown at 4 and 22?C, and 12 surface sediments from the Baltic Sea and the adjacent Skagerrak. In the culture experiments all three proxies showed the expected response with the rise of temperature, but their absolute values were not always in line with existing marine core top calibrations, especially for the OH-GDGT% index. Of the two proxies based on the distribution of OH-GDGTs, the RI-OH index shows no increase with increasing mean annual SST, whilst the RI-OH? index shows only a linear correlation with SST when the sediments from the Bothnian Sea and Bay area, with a reduced salinity and increased lateral sediment influx, are omitted from the dataset. Two sedimentary Holocene records from the Arkona and Gotland basins were studied, the latter in high resolution. In the brackish phase of the Baltic Sea (the Littorina Sea stage), the RI-OH? index shows a good correlation with the TEX_86^( L), an established temperature proxy in the Baltic Sea, and can be used to identify important climatic events. However, during the preceding Ancylus Lake phase the RI-OH? (and RI-OH) index records far too high values, resulting in anomalously high SST estimates. This is probably because freshwater thaumarchaea adjust their OH-GDGTs differently, as has been shown for thaumarchaea in Lake Lugano?s water column. In the Littorina Sea, the Ancylus Lake and the Yoldia Lake phases of the Baltic basin, the record of the RI-OH? index, thus, most likely reflects both changes in temperature and salinity. Overall, our study indicates that a reduced salinity increases the values of the RI-OH? (and RI-OH) indices substantially and this should be considered when applying these proxies in other settings

Assessing marine nitrogen cycling dynamics under altering redox conditions using depositions of sapropels S1 and the ambiguous S2 in the Eastern Mediterranean Sea

The eastern Mediterranean Sea (EMS) sedimentary record is periodically interspersed with organic- rich ?sapropel? layers. Sapropels are characteristic of basin-wide anoxic events, triggered by precession-forced insolation maxima. Relatively subdued insolation maxima, however, are not always expressed as distinct sapropel events. The EMS sedimentary record hereby allows anoxia and nitrogen (N) cycling tipping points to be investigated, which may act as analogues for modern deoxygenation. To this end, we investigated a ~68 kyr EMS sedimentary record, containing the well-established sapropel S1 (deposited in two phases: S1a [~10.5?8.5 ka BP] and S1b [~7.8?6.1 ka BP]) and sediments timed to the ambiguous S2 sapropel (~53 ka BP). We focus on lipid biomarkers of microorganisms to reconstruct key components of the N cycle: (1) anaerobic ammonium oxidation (anammox) using ladderanes and a stereoisomer of bacteriohopanetetrol (BHT-x), (2) dinitrogen gas (N2) fixation using heterocyte glycolipids (HGs), and (3) nitrification by Thaumarchaeota using crenarchaeol. During S1, export-productivity (indicated by the barium to aluminum ratio) and anoxia (indicated by redox-sensitive trace elements and benthic foraminifer assemblages) are enhanced. Thaumarchaeota are most abundant in S1a, while anammox is enhanced throughout S1. N2-fixation (indicated by bulk sedimentary ?15N) occurs throughout S1, while the highest heterocyte cyanobacteria abundance is at the S1a termination and S1 interval. Ladderane presence suggests additional episodes of bioavailable N removal between ~69 to 39 cal ka BP. These episodes correspond to brief periods of water column deoxygenation, with anoxia occurring at the sediment-water interface in sediments timed to S2 (53?51 cal ka BP). During these episodes, ladderanes co-occur with the BHT-34R stereoisomer, but not BHT-x. Compound-specific ?13CBHT-34R indicates an anammox source. Our results highlight various modes of operation of the N cycle during the different deoxygenation events. During S1a, a combination of N-loss and P-supply may have reinforced anoxia, by favoring diatom-diazotroph symbiotic consortia. Conversely, a coupling between N2-fixation and anammox was not observed during S1b and the S2-timed interval, either because loss of bioavailable N was insufficient or diazotrophs were nutrient limited. During these periods, anammox may have provided negative feedback on anoxia by quenching primary production

Influence of Irradiance and Temperature on the Virus MpoV-45T Infecting the Arctic Picophytoplankter Micromonas polaris - Data

Arctic marine ecosystems are currently undergoing rapid changes in temperature and light availability. Picophytoplankton, such as Micromonas polaris, are predicted to benefit from such changes. However, little is known about how these environmental changes affect the viruses that exert a strong mortality pressure on these small but omnipresent algae. Here we report on one-step infection experiments, combined with measurements of host physiology and viability, with 2 strains of M. polaris and the virus MpoV-45T under 3 light intensities (5, 60 and 160 ?mol quanta m?2 s?1), 2 light period regimes (16:8 and 24:0 h light:dark cycle) and 2 temperatures (3 and 7?C). Our results show that low light intensity (16:8 h light:dark) delayed the decline in photosynthetic efficiency and cell lysis, while decreasing burst size by 46%. In contrast, continuous light (24:0 h light:dark) shortened the latent period by 5 h for all light intensities, and even increased the maximum virus production rate and burst size under low light (by 157 and 69%, respectively). Higher temperature (7?C vs 3?C) led to earlier cell lysis and increased burst size (by 19%), except for the low light conditions. These findings demonstrate the ecological importance of light in combination with temperature as a controlling factor for Arctic phytoplankton host and virus dynamics seasonally, even more so in the light of global warming

Data from: Establishing cordgrass plants cluster their shoots to avoid ecosystem engineering

1. Vegetated coastal ecosystems such as salt marshes, dunes and seagrass meadows occur at the land-sea interface ? a dynamic environment typified by harsh growing conditions. These ecosystems are known as biogeomorphic landscapes because their functioning depends on biophysical interactions by which organisms engineer landforms to their own benefit. The strength of such biogeomorphic feedbacks depends on plant traits, such as stem flexibility and shoot density. 2. Recent work demonstrated that dune grasses with similar morphological traits can build contrasting landscapes due to differences in their spatial shoot organization. However, in contrast to dune grasses that trap and stabilize sand particles in aeolian landscapes, flow attenuation in aquatic environments can generate scouring around plant stems and cause uprooting, leading to establishment thresholds for young plants. 3. Yet, it remains unknown how findings from aeolian landscapes translate to aquatic systems and how young clonally expanding plants in hydrodynamically exposed conditions overcome these establishment thresholds by optimizing shoot placement. 4. Here, we measured shoot patterns of 90 establishing cordgrass patches (Spartina anglica) at 18 European field sites that cover a broad range of hydrodynamic conditions. Next, we carried out a field experiment to investigate how observed spatial shoot patterns affect plant-sediment feedbacks. 5. Surprisingly, field survey analyses reveal highly consistent clustered shoot patterns, regardless of environmental conditions. Experimental results demonstrate that this clustered pattern minimizes scouring compared to densely clumped organizations typically observed in established patches. 6. Synthesis. In contrast to earlier findings highlighting that establishing dune grasses optimize their landscape engineering capacity via a flexible shoot placement strategy, we find that cordgrass instead follows a fixed strategy that minimizes engineering effects in its early life stages. We suggest that marsh grasses avoid physical stress and associated establishment thresholds in their early life stage, and switch to an ecosystem engineering strategy once established. These findings shed new light on how plant traits interact with their environment to shape the landscape and pave the way for improved restoration designs by mimicking the natural shoot organization of establishing vegetation