How do mussel beds persist in the Canterbury region?

Solving a “paradox” by identifying predator-free biogenic habitats


This project is funded by the Brian Mason Scientific & Technical Trust ( and led by Dr Tommaso Alestra ( in collaboration with Prof Schiel and Dr Thomsen (Marine Ecology Research Group, University of Canterbury).




The project aims to solve a “paradox” about mussel bed dynamics left unanswered by previous research. Intertidal mussel beds in the Canterbury region (along the east coast of the South Island of New Zealand) experience constant and intense predation by crabs and fish, which feed on small, juvenile mussels during high tides. Although juvenile mussels (5-15 mm shell length) seem to have no escape from fish and crab predation, extensive mussel beds are widespread along the Canterbury coastline.

Mussel beds are common in the Canterbury region, despite constant and intense predation on juvenile individuals.

How do mussel beds persist under such extreme predation pressure?

We aim to answer this question by combining classical experimental ecology (field-based manipulations within mussel beds) with cutting edge technologies (3D modelling and printing) to test the importance of predator-free biogenic habitats for juvenile mussel survival.

Our core hypothesis is that biogenic macro- and microhabitats created by seaweeds and adult mussels provide previously overlooked predator-free space for juvenile mussels, allowing them to reach a refuge size (> 15 mm shell length) which makes them resistant to fish and crab predation.


Objectives and methodology

The project has three major objectives.

  1. Testing the influence of biogenic macrohabitats (seaweed canopies) on juvenile mussel vulnerability to predation

Juvenile mussels may be less susceptible to predation when they are associated with large canopy-forming seaweeds such as the native fucoid Carpophyllum maschalocarpum and the invasive kelp Undaria pinnatifida. These seaweeds have long fronds and form canopies covering the underlying substrate.

Canopy-forming seaweeds cover the underlying substrate with their long fronds. Left: the native fucoid Carpophyllum maschalocarpum. Right: the invasive kelp Undaria pinnatifida.


Juvenile mussels may find refuge from fish and crab predation under the canopies of Carpophyllum and Undaria. To test this hypothesis, we will compare the survival of juvenile mussels living inside and outside seaweed canopies of both Carpophyllum and Undaria. To test the importance of seaweed canopies as predation refuge, juvenile mussels (settled on plastic tiles covered with a nylon carpet) will be placed both in canopy-covered and canopy-free areas. In both habitats, we will use metal mesh cages to protect the mussels from fish and crabs and assess their survival in the presence and absence of predation.

Experimental set-up. Left: juvenile mussels settled onto a plastic tile covered with a nylon carpet. Right: juvenile mussels enclosed within a metal mesh cage to exclude predators.


  1. Testing the influence of biogenic microhabitats (spaces embedded within seaweed holdfasts and adult mussel clumps) on juvenile mussel vulnerability to predation

Juvenile mussels may also experience less predation within biogenic microhabitats provided by seaweed holdfasts (i.e., open holes and gaps) and clumps of adult mussels (i.e., interstitial spaces among shells).

Biogenic microhabitats within seaweed holdfasts (left) and clumps of adult mussels (right) may provide predation refuge to juvenile mussels.


To test whether these microstructures are less accessible to predators, we will assess the survival of juvenile mussels placed within the microhabitats provided by seaweed holdfasts (of both Carpophyllum and Undaria) and adult mussel clumps.

Experimental set-up. Juvenile mussels will be settled within biogenic microhabitats provided by seaweed holdfasts (open holes and gaps; left) and clumps of adult mussels (interstitial spaces among shells; right).


  1. Testing the importance of the physical architecture of biogenic microhabitats in improving mussel survival

The physical architecture of the biogenic microhabitats may be key in helping juvenile mussels to escape predation, but other chemical or biological mechanisms may also be important. To tease out the relative importance of the physical structure of biogenic microhabitats, we will use modern 3D modelling and printing techniques to create artificial mimics of seaweed holdfasts (of both Carpophyllum and Undaria) and mussel clumps. We will also manipulate the size of the microhabitats by 3D printing mimics of holdfasts and mussel clumps with large and small microstructures.

3D modelling (left) will be used to create artificial mimics of seaweed holdfasts (right) and mussel clumps.


To test whether biogenic microhabitats affect mussel survival primarily through physical mechanisms, we will assess the survival of juvenile mussels associated with both natural holdfasts and mussel clumps and their artificial mimics.

Comparisons between natural habitats (right) and artificial mimics (left) will tease out the relative importance of the physical structure of biogenic microhabitats.


Further developments

We will also expand this research in other directions, for example by testing how the invasion of mussel reefs by Undaria pinnatifida can drive the diversity of small invertebrate assemblages through the formation of habitat cascades.

Mussel reefs support high biodiversity of small invertebrate inhabitants.


In particular, we will test whether: 1) the association between mussels and Undaria holdfasts affects the diversity of the associated invertebrate communities; 2) such an effect is dependent on the physical structure of Undaria holdfasts or on other chemical or biological mechanisms. To test these hypotheses, we will assess the diversity of invertebrates associated with: 1) adult mussels; 2) adult mussels hosting Undaria holdfasts; 3) adult mussels hosting Undaria holdfast mimics.

Holdfasts of Undaria pinnatifida (right) and artificial holdfast mimics (left) will be settled onto adult mussels to assess the influence of mussel-Undaria habitat cascades on invertebrate biodiversity.


 Field work


All the experiments will be carried out in the unique marine backyard of the Christchurch area at intertidal rocky reefs in the Lyttelton Harbour and around the Banks Peninsula, where mussel beds and seaweed canopies are highly abundant. Our study will continue a long tradition of marine ecological research along these shorelines.



Collectively, the project will:

  1. solve a scientific paradox and refine New Zealand coastal food web models;
  2. shed light on the nature of the interactions between native and invasive species in New Zealand intertidal communities;
  3. include new, cutting edge methodologies into ecological research and develop approaches applicable to different systems;
  4. highlight novel methods to reduce mussel loss to predation which could be applicable both to mussel farming (to increase production) and conservation strategies (to restore mussel reefs).

We will communicate our results both to scientific audiences through conference presentations and peer-reviewed publications and to the general public through seminars and workshops as part of local initiatives.


Updates and contacts

All the latest updates about the project will be available on the Marine Ecology Research Group Twitter ( and Facebook pages We will post pictures and updates on the project and advertise upcoming public events. You can also contact us on Twitter, Facebook or through this website. We will be very happy to answer questions, provide further information and share ideas.