Mussel Seed Capture Installations (MZI's)

A new technique for harvesting mussel seed has been under construction: Mussel Seed Capture Installations (or MZIs).

Mussel seed fishing takes place in the waters just off the Dutch coasts. These waters are also of great natural value and most of them have been designated as nature reserves under the terms of the Nature Conservation Act or the European Birds and Habitats Directive. As a result, the Netherlands must ensure that it preserves the natural value of these areas. Decisions about mussel fishing prompt widespread social debate and attract political attention. With regard to the future of mussel fishing, the Cabinet is opting for socio-economic development within the conditions set out in the objectives relating to nature and nature-related value.

A new technique for harvesting seed has been under construction since 2000; Mussel Seed Capture Installations (or MZIs). These MZI installations make use of the lifecycle of the mussel. Mussels produce larvae in the spring. These larvae drift in the water for several weeks before latching onto a hard substrate. On the whole, the survival rate is much higher if the larvae can latch onto a substrate that hangs in the water rather than latching directly onto the seabed. After latching on, the mussel is known as brood and develops into seed, and a size that the mussel farming sector can use for bottom culture. Substrates such as ropes and nets are placed in the water in the spring, at a time when large numbers of larvae are present in the water.  

On 21 October 2008, the Ministry of Agriculture, Nature & Food Quality, the mussel sector and nature organisations signed an agreement entitled ‘Transitie mosselsector en natuurherstel in de Waddenzee’ (Transition mussel sector and nature restoration in the Wadden Sea), in which the parties undertake to work together to develop a mussel sector that is not dependent on bottom seed fishing by 2020. In October 2009, the Policy on Mussel Seed Capture Installations (Beleid Mosselzaadinvanginstallaties) was approved for the period 2010 up to and including 2013. This Policy grants 500 hectares for MZIs at 9 locations in the Wadden Sea and 200 hectares at 4 locations in the Oosterschelde. The areas to be allocated in the first phase (2010-2011) are 203 hectares in the Wadden Sea and 110 hectares in the Oosterschelde. In 2009 (the trial year), some 514 hectares were allocated in the Western Wadden Sea and 178 hectares in the Oosterschelde.

Scaling up of the areas

The scaling up of the areas for MZIs in the Western Wadden Sea, in combination with the mussel plots and increasing acreage for wild mussel banks and other shellfish such as Japanese oysters and American razor clams, may have ecological implications.

Scaling up the seed capture with the MZI systems throws up a number of uncertainties and gaps in our knowledge. The effects of MZI systems and activities on the surrounding area include the capacity through filtration of phytoplankton and recycling of nutrients, deposits on the bottom structure and bottom fauna, and disturbance or attraction of birds, seals, prawns or the formation of mussel seed banks. Alongside this, wear and tear may generate litter in the form of micro plastics, buoys, ropes or nets. These objects or substances could have an adverse effect on organisms in the marine environment. And finally, MZIs affect the landscape and activities in the immediate surroundings. The main question stemming from Ministry of Agriculture, Nature & Food Quality policy is whether MZIs will have a positive or negative effect on the preservation objectives for Natura 2000 areas.

Knowledge questions

How will the presence of MZIs in the Western Wadden Sea and the Oosterschelde affect:

  1. the capacity through filtration of phytoplankton and recycling of nutrients;
  2. the bottom structure and bottom fauna through deposits of organic material;
  3. the formation of mussel seed banks through secondary settlement;
  4. disturbance or attraction of birds and seals through MZI activities;
  5. the generation of litter through wear and tear?
    In respect of the mussel seed itself:
  6. What are the developments in growth and survival rates for mussel seed and the yield of MZIs in relation to the position?

Monitoring programme 2009

In 2009, the Ministry of Agriculture, Nature & Food Quality set up an extensive monitoring programme to monitor the effects of MZIs on the capacity, and the bottom and disturbance levels, for a provisional term until 2014. In 2009, this involves:

  • putting a method for measuring the local effects of MZIs on capacity into operation;
  • making an initial measurement of any accumulation of organic material in close proximity to the MZIs;
  • making an inventory of litter (macro plastics) on the basis of current observations;
  • developing a method for quantifying the growth and death rates of MZI seed during the course of a season for the purposes of capacity calculations.