Mussels are bivalve molluscs. New Zealand has 22 species of mussel including the blue mussel (kuku), little black mussel (hauea) and the ribbed mussel (pukanikani). Depending on the species, mussels are found in many different marine habitats – intertidal areas, rocky reefs and subtidal locations.
New Zealand’s best-known mussel is the endemic green-lipped mussel (Perna canaliculus). They make their home on rocks and solid surfaces around the country’s coastline. Green-lipped mussels are an important part of the New Zealand economy. The mussel industry is worth over $200 million in food exports and more than $40 million in biopharmaceuticals and health supplements. Today, most green-lipped mussels are sourced from mussel farms.
Until the 1960s, mussels were harvested by dredges (boats that scraped beds of mussels from the seafloor), particularly in the Hauraki Gulf and Marlborough Sounds. As the mussel beds were ‘fished out’, poachers moved in and used scuba gear to harvest mussels from intertidal rocks – even though it was illegal to do so at the time. Most mussel beds did not recover. Without the existing adult mussel beds, the juvenile spat had few places to permanently settle. As forested land was cleared and wetlands were drained, soil was washed into the sea, smothering regenerating beds.
Mussels’ role in the ecosystem
Mussel beds play several important roles within marine ecosystems. Mussels are filter feeders. They draw in large amounts of seawater to trap phytoplankton, their food source. One mussel can filter up to 350 litres of seawater daily – equivalent to three full bathtubs. As the mussels filter the water, they also remove sediments and other substances that make the water murky. In the early part of the 20th century, seabed mussels were capable of filtering the entire Firth of Thames on a daily basis. Now, it would take 2 years for the remaining mussel beds to do the same job.
Mussel beds also provide a habitat for other sea creatures. They act as nurseries for juvenile fish to shelter and grow and are home to invertebrates and other types of marine life. Snapper, crabs and crayfish eat mussels, so recreational fishers are often found near mussel farms.
Restoring mussel reefs to enhance water quality and marine life diversity
Initially, mussels were reintroduced to the Hauraki Gulf for economic reasons. However, one New Zealand group is more interested in the ecosystem services that mussel reefs can provide. The Mussel Reef Restoration Trust hopes to create seabed mussel reefs – something that has never been attempted before.
In December 2013, the Trust dropped 7 tonnes of mussels near Waiheke Island. Several months later, divers discovered that the mussels had matted together, and a diverse ecosystem was beginning to form. The next drop was nearly 10 times larger – 3.5 million live adult mussels were seeded across a restoration area the size of eight football fields. The mussels, which did not meet supermarket size requirements, were donated by North Island Mussels Ltd.
The Trust plans to establish three large demonstration beds and support local communities to create smaller seedbeds. Back on land, the Trust is partnering with local educational and research institutes to attract and engage young scientists into marine research.
Use our collection of resources on farming green-lipped mussels to discover how these mussels are farmed and how a tiny parasitic crab affects the mussel industry.
Learn more about mussels and filter feeding with this video.
Nature of science
Collaboration is an important component of science. The Mussel Reef Restoration Trust team members bring a variety of skills in planning, engineering and communication to the project. The team partners with community groups, iwi, Auckland University, mussel producers and more to achieve their goals.
Visit the Mussel Reef Restoration Trust’s Revive Our Gulf website. Included on the site is a downloadable worksheet to enable teachers to easily show students the power of mussels as ecosystem engineers and water cleaners and a poster that displays the diversity of life found in a mussel reef.
Secondary school student Yasmine Dai’s investigation into the filtering ability of green-lipped mussels won the 2015 Auckland Science Fair NIWA Premier Gold Award is covered in this news story.