Green-lipped mussels (kūtai, Perna canaliculus) are endemic to New Zealand. Discover how these mussels are farmed, and how a tiny parasitic crab affects the mussel industry.

New Zealand’s unique green-lipped mussels

Green-lipped mussels thrive in New Zealand’s clean, nutrient-rich waters. They grow abundantly in the intertidal zone and in shallow coastal waters. The article Life of a green-lipped mussel details their transition from a free-swimming form to the immobile adult form that is a familiar sight on rocks and wharf piles.

Mussel farming: a very Kiwi industry

New Zealand’s mussel farming industry began in the late 1960s, after overfishing caused the collapse of wild mussel harvesting. Originally, individuals set up mussel farms on a small scale, sharing ideas and experimenting with new technologies. The industry has developed rapidly – now, green-lipped mussels (exported under the trade name GreenshellTM) are New Zealand’s most important farmed marine organism. They account for about three-quarters of New Zealand’s total earnings from aquaculture exports (with king salmon and Pacific oysters accounting for most of the remainder). Learn more about mussel farming in New Zealand’s green-lipped mussel industry.

The mussel and the crab: an ancient relationship

Ever opened a green-lipped mussel to find a tiny crab nestled inside? That’s the New Zealand pea crab. It lives within mussels and other crustaceans. In some mussel populations, well over half the mussels contain a pea crab.

New Zealand pea crabs are parasites – they have a negative impact on their host mussels. Pea crabs steal phytoplankton that mussels have collected for food, damage the mussel’s gills and cause nodules on the mussel shell.

Until recently, it wasn’t known how pea crabs affected the mussel industry, but now, Oliver Trottier, a scientist at Leigh Marine Laboratory (University of Auckland), has shown that pea crab infestation makes farmed mussels up to a third lighter. This affects the price that mussel farmers can command for their product and ultimately decreases the industry’s profits. Read about Oliver's research in Testing how pea crabs affect mussel farming.

Getting to grips with pea crabs

Oliver and his colleague Jessica Feickert (also a scientist at Leigh Marine Laboratory) have been investigating the biology of the pea crab. They are looking for ways to decrease the level of pea crab infestation on mussel farms.

Oliver and Jessica have shown that male pea crabs may use pheromones to locate female crabs at mating time. They have discovered previously unseen stages in the pea crab’s life cycle, and in the process, they’ve learned a lot about the surprising habits of the pea crab – such as how they seem to ‘tickle’ a mussel for hours on end to get it to open its shell!

The articles Life of a pea crab and Getting into and out of mussels add insight into these interesting creatures.

Could biocontrol keep pea crabs out of mussels?

Biocontrol of the New Zealand pea crab explains how Oliver and Jessica hope to use their findings to develop a biocontrol approach that limits pea crab numbers on mussel farms. They are focusing on developing a pheromone trap that could confuse male pea crabs and stop them from finding females to mate with. They are also looking at ways to stop larval pea crabs from settling in farmed mussels.

Take up the challenge

The activities Investigating how pea crabs affect supermarket mussels, Similarities and differences: wild and farmed green-lipped mussels and Finding a female give students the opportunity to learn more about mussels, pea crabs and their impact on the aquaculture industry.

    Published 25 June 2013