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opencc-by-4.0Nov 2024View details →

Wadden Sea drifter trajectories 2023

Trajectories of twentyfour oceanic drifters deployed in the Wadden Sea just east of the island of Texel on 14 November 2023. The drifters are so-called Stokes drifters, built by <a href="https://metocean.com/products/stokes-drifter/">MetOcean</a> in Canada. They are small, white, floating devices that are designed to follow the water motion in the Wadden Sea. The drifters are equipped with a GPS and a satellite transmitter, so that we can track their position in real time. The data have not been cleaned for outliers. Note that transmission frequencies change during the trajectories (as indicated in the time variable). An interactive visualisation of the drifters can be seen <a href="https://oceanparcels.org/driftermap.html?fn=waddendrifters2023_detailed.json&anim_freq=0.2" target="_blank" rel="noopener">here</a>.

Figure 2 in Onset and duration of gray seal (Halichoerus grypus) molt in the Wadden Sea, and the role of environmental conditions

Figure 2. To aid interpretation of the data, this figure presents a progression of data processing in a simulation. (A) Observations of potential absolute seal numbers on a sandbank against day of the year, using assumptions described in the text. (B) The relative proportions (prop.) of seals in each molt phase changes over time. (C) The proportion of seals in pre-visible-molt (light blue) decreases over time and the proportion in post-molt increases, the seals in early- and late-molt (green lines) peak at certain times. (D) Over time, the numbers of seals on the sandbanks that are in each visible molt phase (i.e., excludes seals in pre- and post-molt), (E) Over time, the proportions of seals in visible molt that are in early- or late-molt. (F) The proportion of seals in visible molt that were in late-molt. Note that the change over time in this proportion is linear (the horizontal dashed line indicates 50% in each stage, which occurs in this simulation on day 105).

Figure 4 in Onset and duration of gray seal (Halichoerus grypus) molt in the Wadden Sea, and the role of environmental conditions

Figure 4. The proportion of wild gray seals (given an observation quality = 1) in different molt stages over time. The proportion in pre-visible-molt decreases and that in post-molt increases over time, while numbers in early- and late-molt peak during the molt period. Data are represented by the colored dots, the lines indicate the simulation of Fig. 2c.

Figure 6 in Onset and duration of gray seal (Halichoerus grypus) molt in the Wadden Sea, and the role of environmental conditions

Figure 6. Simulations of changes in the proportion of seals in visible molt that were in latemolt, compared to the base scenario (black). These figures show the effect of shorter (red) and longer visible (orange) molt durations (A); shorter early-molt (light green) or shorter late-molt (dark green) durations (B); changes in the day of onset of molt (C); changes in the variability between individuals (SD) (D); and changes in the haul-out percentage during early- and latemolt (E). The base scenario was derived from the parameters from captive seals identified in this study, i.e., visible molt commences on average on day 99, early-molt lasts 8.2 d and late-molt lasts 8.7 d. The standard deviation that defines the variability between individuals is 15 d. This base senario assumed that the haul-out behavior is the same during early- and late-molt.

Figure 1 in Onset and duration of gray seal (Halichoerus grypus) molt in the Wadden Sea, and the role of environmental conditions

Figure 1. Aerial photograph of molting gray seals on a Wadden Sea sandbank. Seals are in pre-visible-molt (A), early-molt (B), late-molt (C), or post-molt (D). Recognizable adult males were noted separately. The quality was not always consistent due to glare or sand, and therefore seals were defined to have high (1), moderate (2), bad (3), or inadequate quality (4). The contrast of the pelage color in the true picture (upper image) was automatically selected using color select in Adobe Photoshop CS (lower image). The brown old fur was colored orange, and the grayish new fur was colored blue showing an even stronger contrast between early- and late-molt.

Figure 3 in Onset and duration of gray seal (Halichoerus grypus) molt in the Wadden Sea, and the role of environmental conditions

Figure 3. The molt progress of nine captive gray seals recorded daily in 2010. The individuals were kept at two locations (Dolfinarium and Ecomare), had different origins, ages, and sexes (see y-axis). Note that the onset and end of molt varied per individual but the duration of the phases in the visible molt (early-molt and late-molt) were similar.

opencc-by-4.0Apr 2021View details →

Fig. 1 in Lungworm infections in harbour porpoises (Phocoena phocoena) in the German Wadden Sea between 2006 and 2018, and serodiagnostic tests

Fig. 1. Annual comparison of lungworm prevalence in harbour porpoises stranded along the North Sea coast of the German federal state SchleswigHolstein between 2006 and 2018. The median of total deaths (19 ± 9.23, black line), uninfected cases (10 ± 6.83, dotted line) and positive cases (8 ± 5.04, dashed line) are additionally depicted.

opencc-by-4.0Apr 2021View details →

Fig. 2 in Lungworm infections in harbour porpoises (Phocoena phocoena) in the German Wadden Sea between 2006 and 2018, and serodiagnostic tests

Fig. 2. MSP-ELISA results of the 245 samples from harbour porpoises assignable to a specific infection status. Green = lungworm negative (born in captivity); light blue = presumed lungworm negative sera (negative direct detection); dark blue = presumed lungworm negative whole blood (negative direct detection); light red = lungworm positive sera (direct lungworm detection); dark red = lungworm positive whole blood (direct lungworm detection). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

opencc-by-4.0Apr 2021View details →

Fig. 3 in Lungworm infections in harbour porpoises (Phocoena phocoena) in the German Wadden Sea between 2006 and 2018, and serodiagnostic tests

Fig. 3. Immunoblot pattern of (presumed) lungworm negative (lane numbers indicated in blue: 1–5 = animals born in human care; 2–5 sampled over three consecutive years; 6–8 = no infection detected) as well as lungworm positive (lane numbers indicated in red: lane 9 = moderate infection; lane 10 = severe infection; lanes 11–16 = direct lungworm detection) harbour porpoise sera. Lane 17 = D. viviparus positive control serum, M = Spectra™ Multicolour Broad Range Protein Ladder (Thermo Fisher Scientific GmbH, Dreieich, Germany). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

opencc-zeroApr 2022View details →

Spatial and temporal variations in salt marsh microorganisms of the Wadden Sea

Salt marshes exist at the interface of the marine and the terrestrial system. Shore height differences and associated variations in inundation frequency result in altered abiotic conditions, plant communities and resource input into the belowground system. These factors result in three unique zones, the upper salt marsh (USM), the lower salt marsh (LSM) and the pioneer zone (PZ). Marine detritus, such as micro- and macroalgae, is typically flushed into the PZ daily, with storm surges moving both salt marsh detritus and marine detritus into higher salt marsh zones. Microbial assemblages are essential for the decomposition of organic matter and have been shown to sensitively respond to changes in abiotic conditions, such as oxygen supply and salinity. However, temporal and spatial dynamics of microbial communities of Wadden Sea salt marshes received little attention. We investigated the dynamics of soil microbial communities across horizontal (USM, LSM and PZ), vertical (0-5 and 5-10 cm sediment depth) and temporal (spring, summer and autumn) scales in the Wadden Sea salt marsh of the European North Atlantic coast using phospholipid fatty acid (PLFA) analysis. Our results show strong spatial dynamics both among salt marsh zones and between sediment depths, but temporal dynamics to be only minor. Despite varying in space and time, PLFA markers indicated that bacteria generally were the dominant microbial group across salt marsh zones and seasons, however, their dominance was most pronounced in the USM, whereas fungal biomass peaked in the LSM and algal biomass in the PZ. Only algal markers and the stress marker monounsaturated to saturated fatty acid ratio responded to seasonality. Overall, therefore the results indicate remarkable temporal stability of salt marsh microbial communities despite strong variability in abiotic factors.

opencc-zeroJun 2022View details →

Trophic structure and origin of resources of soil macrofauna in the salt marsh of the Wadden Sea: a stable isotope (15N,13C) study

Salt marshes exist along the gradient of the marine mudflat to the terrestrial dunes, with a gradient of shore height and associated plant zonation. The lower salt marsh (LSM) extends from the mean high tidal level to 35 cm above that level and is followed by the upper salt marsh (USM). Despite changes in the amount of allochthonous marine input and in abiotic conditions, little is known about changes in the trophic structure and used of basal resources by the soil macrofauna along marine – terrestrial boundaries. Natural variations in carbon stable isotope ratios (δ¹³C signatures) allow insight into basal resources of consumers such as marine algae, terrestrial C3 and C4 photosynthesising plants. Furthermore, variations in nitrogen stable isotope ratios (δ¹5N signatures) allow insight into the trophic position of consumers. We investigated spatial and temporal changes in stable isotope signatures in salt marsh soil macrofauna of the island of Spiekeroog, German Wadden Sea. The range of δ¹⁵N signatures indicated no changes in food chain length across salt marsh zones with consumers in both zones comprising primary decomposer, secondary decomposer and first order predators. However, the trophic position of individual species changed between zones, but in particular with season. Contrasting δ¹⁵N signatures, the range in δ¹³C signatures in the LSM was twice that in the USM indicating a wider range of resources consumed. Bayesian mixing models indicated predominant autochthonous resource use in both the LSM and USM, with the use of marine allochthonous resources never exceeding 29.6%. However, the models also indicate an increase in the use of marine resources in certain species in the LSM with no use in the USM. Overall, the results indicate that the resource use of salt marsh macrofauna varies more in space than in time, with the food web being generally based on autochthonous rather than allochthonous resources. However, there also is trophic plasticity in certain species across both temporal and spatial scales including variations in the use of allochthonous resources. Generally, however, marine input contributes little to the nutrition of salt marsh soil macroinvertebrates.

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Data from: Birds influence vegetation coverage and structure on sandy biogeomorphic islands in the Dutch Wadden Sea.

Small uninhabited islands form important roosting and breeding habitats for many coastal birds.  Here, we assess the role of external nutrient input by coastal birds on the vegetation structure and coverage on sandy biogeomorphic islands in the Dutch Wadden Sea, where island-forming processes depend on vegetation-sedimentation feedbacks.  We Used a combination of bird observations and plant stable isotope (δ15N) analyses, to demonstrate that (i) breeding birds transport large quantities of nutrients via their faecal outputs to these islands annually and that (ii) this external nitrogen source influences vegetation development on these sandy, nutrient-limited, islands. We further discuss how this avian nutrient pump could impact island development and habitat suitability for coastal birds and discuss future directions for research. For the conservation of both threatened coastal birds and sandy back-barrier islands and the design of appropriate management strategies, we argue that three-way interactions between birds, vegetation and sandy island morphodynamics need to be further elucidated.    Methods Data stored in this repository are bird counts from all three islands [Breeding_total.csv] and the relation between total faecal excretion rates (estimated using bird counts) and average vegetation coverage (estimated using satellite imagery) [Vegetation_bird.csv]. Additionally, we gathered data in the field including vegetation charactersitics [field.data.xls], isotopic data of the vegetation [new_isotopes.csv] and soil charactersitics [Soil_prop.csv]. Detailed description of these methods and the results can found in the accompanying publication (Reijers et al. STOTEN).

opencc-by-4.0Jul 2024View details →

opencc-zeroJan 2023View details →

Channelling of basal resources and use of allochthonous marine carbon by soil arthropods of the Wadden Sea salt marsh

Salt marshes are located between the marine and terrestrial systems. Because they form as sediment accumulates, they comprise a gradient of shore height with differing inundation frequencies and associated abiotic soil conditions. Along this gradient, both autochthonous vascular plant resources and allochthonous marine algal or detrital resources are available, with the availability of both varying with season and salt marsh zone. However, little is known about the importance of either resource for the soil animal food web. We investigated both spatial and temporal resource use of the soil macro- and mesofauna of the salt marsh using neutral lipid fatty acids (NLFAs). Generally, irrespective of season and zone the soil animal food web relied on carbon originating from autochthonous vascular plants and associated bacteria and fungi, with the role of bacteria generally exceeding that of fungi. However, the channelling of fungal resources consistently peaked in October, whereas seasonal changes in the channelling of plant and bacterial resources varied among salt marsh zones. Further, variations in the channelling of resources with season and zone varied among salt marsh animal species. Although being only minor, allochthonous resources of marine origin contributed to soil food web nutrition across salt marsh zones and seasons. The contribution of algae to soil food web nutrition depended on inundation frequency and season, i.e. algal productivity. Overall, the results demonstrate that the salt marsh soil fauna predominantly relies on autochthonous vascular plant resources, with the contribution of allochthonous marine resources being minor and restricted to few taxa.

opencc-zeroApr 2023View details →

Vessel noise exposures of harbour seals from the Wadden Sea

The North Sea faces intense ship traffic owing to increasing human activities at sea. As harbour seals (Phoca vitulina) are abundant top predators in the North Sea, it is hypothesised that they experience repeated, high-amplitude vessel exposures. Here, we test this hypothesis by quantifying vessel noise exposures from deployments of long-term sound and movement tags (DTAGs) on nine harbour seals from the Wadden Sea. An automated tool was developed to detect intervals of elevated noise in the sound recordings. An assessment by multiple raters was performed to classify the source as either vessels or other sounds. A total of 133 vessel passes were identified with received levels >97 dB re 1µPa RMS in the 2 kHz decidecade band and with ambient noise >6 dB below this detection threshold. Tagged seals spent most of their time within Marine Protected Areas (89 ± 13%, mean ± SD) and were exposed to high-amplitude vessel passes 4.3 ± 1.6 times per day. Only 32% of vessel passes were plausibly associated with an AIS-registered vessel. We conclude that seals in industrialized waters are exposed repeatedly to vessel noise, even in areas designated as protected, and that exposures are poorly predicted by AIS data.