Shellfish reefs as shoreline protection – Eastern Scheldt

Lessons Learned

From the experiments in the Eastern Scheldt we found that iron wire cages (gabions; in Dutch: schanskorven) filled with dead oyster shells can:

  • Grow out into living persistent reefs,
  • Reduce erosion of intertidal flats through wave attenuation and trapping and detention of sediment,
  • Increase local diversity in a sandy habitat by providing a hard substrate habitat.

Ecology and morphology

  • Wave impact and substrate availability can be limiting factors for oyster presence in intertidal areas.
  • Which substrate is suitable for oyster settlement and growth is determined by local conditions (e.g. flow velocities and storms).
  • Under the dynamic conditions in the Eastern Scheldt, the substrate for oyster settlement must be artificially fixed.
  • Gabions (schanskorven) are suitable to hold oyster shells under the Eastern Scheldt conditions.
  • A substrate of fixed oyster shells can grow into a living, self-sustaining oyster reef.
  • The position of the oyster reef in the intertidal determines the survival of oyster larvae and the growth of oysters.
  • The addition of grazers can reduce algal cover and may enhance oyster settlement.
  • Both small- and large-scale oyster reefs can attenuate incoming waves, thus reducing erosion of the intertidal flats they protect.
  • Artificial oyster reefs cannot replace existing coastal defense structures, but they can contribute by causing shoal and foreshore accretion under average weather conditions.


  • It appeared to be important to involve parties that:
  • In the initiation phase of the BwN trajectory it is useful to carry out a stakeholder analysis to find out with whom to interact, when and how. Especially in the case of scaling up experiments, a stakeholder analysis is helpful to design a strategy for collaboration and communication with potential opponents and supporters.


  • It appeared to be useful to spend time and effort to careful planning and targeting the communication on building with nature.
  • A mix of communication methods (e.g. press release, movie, excursions) is required to reach different categories of stakeholders.
  • A tangible experiment which can be touched and seen is attractive for policy makers to show their innovative achievements.

Regulatory context

  • Involve parties knowledgeable in quickly finding out about procedures and required licences and ask them to help processing the necessary forms.
  • Start discussions with stakeholders who could oppose the initiative well before submitting the requests for the necessary permits.
  • The new Dutch nature conservation law (2012) facilitates the legislative and juridical procedures.


  • BwN experiments require different types of knowledge derived from different sources, such as models, measurements and experience/expert judgement. To fill knowledge gaps in the field of morphology and ecology, it appeared to be useful to organise workshops bringing together professionals, practitioners and researchers who jointly shared and co-created new knowledge.

Dealing with uncertainty

  • Uncertainties typical of shellfish reefs include: the formation of a living reef, its longevity, and the increase in sediment deposition / reduction of erosion. Monitoring the ecological and morphological effects of the shellfish helps reducing these uncertainties.
  • Any monitoring programme has to be preceded by a baseline study.
  • Experiments like this need a flexible planning that allows regular adaptation and learning.
  • Stakeholders and the general public tend to expect results of this type of experiments within one year. It has to be clear from the start that this is about long-term development. Effects on ecology, morphology and dike stability can only be made visible after a number of years. On the other hand, proponents of this kind of measures need to realize that policy makers and other decision makers do not need 99% or 95% confidence for taking decisions. Communication of preliminary results can therefore be very relevant.

Economic value of building with nature

  • One needs to show how building with nature can work before its economic benefits can be demonstrated. Yet, the costs of the initiative should be made as explicit as possible from the very beginning.
  • Acceptability and economic viability of shellfish reefs can be enhanced by financial and institutional arrangements that bring together water safety, aquaculture and nature conservation networks (coupled functionality).