Restoration of the stocks of the European oyster (Ostrea edulis) in the German North Sea

Within the framework of this research and development project ("E+E Vorhaben"), sponsored by the Federal Agency for Nature Conservation (BfN), methods and procedures for sustainable stock establishment of the European oyster in the German North Sea will be developed and tested at pilot scale for the first time. The project RESTORE is based on recommendations of the BfN feasibility study (Gercken & Schmidt 2014) and addresses open research questions.

The results of this study will be used to design a large-scale restoration program to establish a healthy stock of these highly endangered oysters in Europe and further restore oyster beds at selected locations in the German North Sea.

Project term 2016 - 2019 ("Preliminary investigation")

The reintroduction of this once endemic oyster in the German North Sea is considered a marine conservation measure. It is professionally supervised by the Department of Marine Nature Conservation of the BfN and carried out by AWI. In order to restore the stock of this species sustainably, nature conservation legislation has to be reviewed and technological and biological issues need to be overcome to allow final recommendations for a long-term restoration program.

Scientific and technical objectives

Within the scope of the present research and development project, the scientific and technological framework is created for a successful restoration of European oyster stocks in the German North Sea. While observing nature protection requirements, field studies were carried out at potential recovery sites to test various technologies. The goal is to enable and enhance the settlement, growth and fitness of Ostrea edulis.

The following insights were gained:

  • Evidence of growth and health (biological fitness)
  • Identification of broodstock populations within Europe (oysters seeds to reintroduce)
  • Recommendations for suitable sites
  • Recommendation for appropriate technologies

First results:

In spring 2017, young seed oysters were deployed in oyster cages at an offshore area north of the island of Helgoland. Juvenile oysters were sampled from this field experiment regularly to gain growth and fitness data. Sampling was carried out by research divers using the AWI research vessels FS Heincke, FS Mya II and FK Uthörn. The following studies were carried out in the AWI laboratories at Helgoland, Sylt and Bremerhaven.

The results show excellent growth and a good health status of the native oysters tested under today's environmental conditions in the German North Sea. The biological suitability for a future restoration is assessed positively by these results.

Further experiments delivered comprehensive findings on the settling behavior of O. edulis larvae on the substrates available in the German Bight. The successful settlement of the larvae is an important element in the long-term restoration.

With respect to defined site-selection-criteria, multiple sites within the German SAC Borkum Reef Ground were selected, which are suitable for future restoration measures. The establishment of a pilot reef here is planned for the next year.

Projekt term 2019 - 2022 ("Prime intent")

The results obtained in the preliminary investigation serve as a basis for the implementation of the prime intent and for its scientific monitoring. The prime intent consists of the establishment of a pilot reef in the marine conservation area Borkum Reef Ground. This includes the development of a concept for the pilot reef, the construction of the reef and comprehensive ecological and technological accompanying studies.

Scientific and technological goals

In the prime intent, further necessary findings for the development of a restoration programme will be worked out in order to establish a healthy population of this highly endangered oyster species and its ecosystem, the oyster reef, at selected locations in the German North Sea. The following goals are in focus:

  • Construction of a pilot oyster reef in the Natura 2000 site Borkum Reefground (BRG)
  • Construction of extended test areas in the NCA BRG with selected substrates
  • Extensive under water documentation of the reef structure
  • Evaluation of reef design and identification of suitable technologies for large scale restoration efforts
  • Development of planning and implementation guidelines for oyster restoration measures in the German North Sea Economic Exclusive Zone (EEZ)
  • Pilot tests in the NCA "Helgoländer Felssockel"

Besides the prime intent, the construction of the pilot reef, a close scientific monitoring is in preparation and starts with the construction of the pilot reef. This monitoring aims at providing conclusions on the growth of the oysters and the development of the associated biocoenosis.