Wadden Sea

The natural processes continue mostly uninterrupted across the vast majority of the World Heritage site, and the Wadden Sea remains one of the most dynamic and valuable tidal areas in the world. Considerable past interference (prior to inscription) (IUCN, 2009), through halting channel migration, fixation of dunes, blocking overwash transport and developing and protecting tidal marshes (Kloepper et al., 2017) raises management challenges in how to maintain these processes through ongoing management interventions in the context of a changing climate (Kloepper et al., 2017). Since then, there were some small cases where natural processes were re-established, and there are probably more cases to come. At the same time the naturalness of the sediment processes close to the mouth of river Elbe (and also at other estuaries) has been reduced due to further deepening of this estuary. More effort is required to understand the relative importance of the major sediment transport processes in order to respond to sea level rise and other climate change associated threats in the future (Kloepper et al., 2017).

These processes continue to function well within the intertidal ecosystems despite considerable interference in the past (prior to inscription) (IUCN, 2009). Natural dynamics occur mainly on the uninhabited parts of the site, such as the the barrier islands without coastal protection and uninhabited islets. However, to keep the Wadden Sea healthy despite sea level rise, nature restoration projects will be necessary, especially in inhabited areas. Initial projects such as the opening of summer dikes achieved success in restoring some of the natural dynamic processes (CWSS, 2010). Further projects such as the dune activation projects in the Netherlands have also been shown to increase dynamics (Kloepper et al., 2017), which will enhance ecosystem functionality. Some concerns have, however, been raised in the ongoing function of estuarine system, particularly the rivers Elbe, Weser and Ems, which experience high levels of industrial activity which has led to impacts on morphology, hydrography (including tidal amplitude), and loss of freshwater and brackish marshes (Kloepper et al., 2017), albeit some of which occurred before inscription with the subsequent implementation of Habitat and Water Framework Directives now improving the situation (Kloepper et al., 2017). In recent years Integrated Management Plans were developed for the estuaries of Elbe, Weser and Ems. In these plans, mainly developed within the framework of Natura 2000, measures required towards achieving the good status for habitats and species have been outlined. Measures for restoring foreland habitats are covered for most parts, whereas measures targeting aquatic habitats (dredging, dumping, fisheries) due to a lack also of political power are covered to a lesser extent.
Nevertheless, the plans are a major step forward towards meeting the target. It is becoming increasingly obvious, that achieving the good status is a long term process, especially in the Ems Estuary due to the very specific situation and the strong linkage to restoring tidal dynamics (Schuchardt and Scholle, 2017).

The Wadden Sea remains of low concern overall as a key site for migratory birds along the East Atlantic Flyway. Monitoring of all the bird species in the World Heritage site is thorough and well established, with monitoring and population development calculations in the entire Wadden Sea having taken place for almost 30 years (e.g. Ens et al., 2009; Laursen et al., 2010; Hôtker et al., 2010; van Roomen et al., 2012; Koffijberg, 2015; Blew et al., 2016; Thorup et al., 2016; Kloepper et al., 2017; van Roomen et al. 2025).

According to the most recent QSR (Kleefstra et al. 2022) the number of species with a negative long-term trend went up from five to 16 in the first three QSRs, but now dropped once again to 13 species, while the number of species with a positive trend did not change substantially: eight in 2004, eight in 2009, six in 2017 and seven in 2022. The same is true for species with stable numbers: 15 in 2004, 12 in 2009, 12 in 2017 and 14 in 2022. The short-term trends show fewer changes, apart from the QSR from 2004. The number of increasing, stable and decreasing species were pretty consistent in the QSR’s of 2009, 2017 and 2022. In comparison with the QSR of 2017 more species show an increase in the short and long term, while the number of decreasing species went down in the long term (but not short term).

Factors inside the World Heritage site potentially impacting breeding, migrating and wintering birds negatively include indirect effects of fisheries activity (available food resources) and direct effects of human disturbance (incl. hunting and tourism) and predation (especially during the breeding season) (IUCN Consultation, 2017). As with the other values, climate change represents the greatest threat through disappearing foraging and breeding habitat by sea-level rise, alterations in the food web and emerging phenological mismatches, both inside the site and along the Flyway (Reneerkens, 2020).

In the framework of the Wadden Sea Flyway Initiative, fourth total count documented a remarkable 233 waterbird species, tallying over 20 million individuals, with nearly 70% belonging to 67 dominant species in EAF coastal sites (Agblonon et al. 2023). Long-term trends of 35 species and sub-species of migratory birds in the Wadden Sea over the last 36 years show increasing numbers for 9 species, stable trends for 12 species and a decline in numbers for 14 species. Short term trends show a slightly more positive picture with 10 species increasing, stable (or uncertain) trends for 14 species and a decline for 11 species. Species that increased in both the long and short term are Eurasian Spoonbill (Platalea leucorodia), Eurasian Wigeon (Mareca penelope), Northern Pintail (Anas acuta), Northern Shoveler (Spatula clypeata), Common Ringed Plover (Charadrius hiaticula) (psammodroma/tundrae-subspecies), Northern Lapwing (Vanellus vanellus) and Sanderling (Calidris alba). Species that have shown a positive trend in the short term but not in the long term are Common Teal (Anas crecca), Common Ringed Plover (hiaticula-subspecies), European Golden Plover (Pluvialis apricaria) and Ruff (Calidris pugnax). Species that continue to decline in both the long and short term are Mallard (Anas platyrhynchos), Common Eider (trend starts 1992/93), Eurasian Oystercatcher (Haematopus ostralegus), Pied Avocet (Recurvirostra avosetta), Bar-tailed Godwit (Limosa lapponica) (taymyrensis-subspecies), Common Redshank (Tringa totanus) (totanus-subspecies), Ruddy Turnstone (Arenaria interpres) (Scandinavian-Western Russian population), European Herring Gull (Larus argentatus) and Great Black-backed Gull (L. marinus). The
numbers of Curlew Sandpipers (Calidris ferruginea) and Eurasian Curlews (Numenius arquata) have decreased in the short but not in the long term. In the long term, the Danish and Dutch parts of the Wadden Sea show the highest numbers of positive trends (for 16 and 17 species respectively), whereas in the German parts of the Wadden Sea many species decrease in number (20 in Schleswig-Holstein and 22 in Lower Saxony). In the short term, this picture hardly differs for the Danish Wadden Sea, but the number of species that still show an increase is much smaller in the Dutch part (8), where many species show a stable and/or uncertain recent trend (20 species). The latter also applies to the German parts of the Wadden Sea (22 and 17 species stable or uncertain in Schleswig-Holstein and Lower Saxony respectively) and fewer species show a negative trend (6 and 16 respectively) (Kleefstra, et al. 2025).

The Wadden Sea is developing a new action plan focused on improving breeding success for birds, particularly addressing the impact of predation. This will involve a workshop in September 2025, and the insights gained will contribute to updating the Breeding Bird Action Plan.

Overall, given the climate change issues along the entire flyway up to the Arctic, the pressure on feeding and breeding habitats by the advancing sea level rise, and also the pressure from growing numbers of mammalian predators on the breeding population of coastal birds in the Wadden Sea (most of then also migratory along the flyway), the state is considered to be of "High Concern" and the trend "Deteriorating".

There is no indication of significant change in species richness since inscription in 2009, when baseline data (e.g. Marencic, 2009; Wolf et al., 2010) was collected.
Seagrass populations have seemingly reached their optimum extent in the last five years following a steady increase in bed area since the mid-1990s (Kloepper et al., 2017), and new meadows have even appeared south of the Rottums and near Griend in the Netherlands (Kloepper et al., 2017). The most recent QSR shows the natural expansion of salt marshes has continued with a natural expansion of the barrier-connected island salt marshes and foreland salt marshes in Schleswig-Holstein. The total salt-marsh area in the Wadden Sea increased by roughly 6,000 ha since the first trilateral survey of 1995/2001 (Elschot et al. 2024).

Subtidal habitats are reported to have shown an overall increase in quality and quantity since 2010 according to mapping of the subtidal zone of the Wadden Sea (Kloepper et al., 2017). Although not explicitly quantified, it can be assumed that human activities in the Wadden Sea, such as bottom-contacting fishing, dredging and coastal protection measures, can lead to habitat destruction and thus alter natural dynamics. However, to our knowledge, the extent of such impacts has not changed significantly since the last QSR. On the other hand, first measures have been taken in the Netherlands to exclude shrimp- and mussel seed fisheries in parts of the Wadden Sea and in 2021 these areas were further extended. Since 2017 some more areas in the Schleswig-Holstein Wadden Sea have come closer to the goal of an increase of geomorphologically and biologically undisturbed subtidal areas, as mussel fishing was prohibited. However, shrimp fishing is still allowed. That means that the third Wadden Sea Plan goal of an increased area of, and a more natural distribution and development of natural mussel beds and Sabellaria reefs is still quite far from being reached (Ricklefs et al. 2022). The increasing number of invasive species like the Pacific oyster (see thematic report on Alien Species) in a certain sense can be considered as a further dynamic impact on the Wadden Sea, but certainly also as a loss of naturalness as key feature of Wadden Sea conservation. It was found that pure sublittoral mussel beds no longer occur north of the Elbe River. Only mixed beds of mussels and oysters still exist here (Oyssel beds). Furthermore, there are indications that in these beds the number of blue mussels is decreasing while that of oysters is increasing and oysters are increasingly also colonising seafloor areas without any hard substrate. Hard substrates on the other hand, at least in the North Frisian Wadden Sea, are increasingly formed by the invasive slipper limpet (Crepidula fornicata) (Ricklefs et al. 2022).

Some salt marshes, particularly on the mainland coast, are in a rather bad shape, in particular due to heavy coastal engineering impacts such as strong drainage systems. Careful restoration projects as part of the daily management of the competent authorities are required for those sites and could certainly increase species richness there and return to a more 'natural' state (Kloepper et al., 2017). Such restoration projects are likely to begin being implemented soon under the EU Nature Restoration Law, including the opening of summer dikes and re-wetting efforts.