Guidance The Waddenzee and Zeeland delta

Index section The Waddenzee and Zeeland delta

Introduction

The Waddenzee (Wadden Sea) and the Zeeland delta are the two large areas in the Netherlands in which tidal influence is very visible. Tidal areas, by nature very dynamic, are where alternating processes of erosion and accretion create new pioneer situations.

Many plant and animal species are adapted to tidal environments and can cope with their habitat being submerged by the incoming tide every day. These species are largely restricted to tidal zones. Almost all the tidal areas in the Netherlands are designated nature reserves.

The variation in duration of submergence, currents and salinity produces a great range of ecotopes in the tidal area. However, the quality and area of many of these ecotopes (including saltmarshes and mussel beds) are currently at risk because of human interventions. Some ecotopes have disappeared, such as the transitional zones between saltmarshes and marsh.

Saltmarshes are the higher-lying vegetated parts of the tidal area. Many of their characteristic plant species rarely occur in other habitats. They are important nesting areas for ducks, waders and sea birds like gulls and terns, and serve as high tide roosts for birds that forage on the mudflats.

The damming of inlets, particularly the Zuiderzee, Haringvliet and Grevelingen, has had huge repercussions for plant and animal life the Waddenzee and Zeeland delta.

The tidal areas are important as spawning areas and nurseries for fish like sole and plaice. Also large numbers of shellfish occur like the mussel, cockle and oyster.

Shellfish numbers fluctuate strongly from year to year; in years when numbers are low, shellfish fishery can negatively affect numbers of birds.

The water quality of the Waddenzee and Zeeland delta has improved. Among the species to have profited, particularly in the Waddenzee, are seals and sandwich tern. The improved water quality has also led to a slight improvement in numbers of migratory fish.