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Scientists make break-through in saving freshwater mussels

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By Milthon Lujan

New Zealand.- NIWA scientists have made an important breakthrough in their efforts to save New Zealand’s freshwater mussels, or kakahi.

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Kakahi were once a valuable food source for Maori. Freshwater mussels also play a crucial role as indicators of the health of waterways and all three kakahi species in New Zealand are in decline. Kakahi are often found tucked under banks, in shady pools and partly submerged in shady, soft-bottomed streams.

NIWA Ecotoxicology Scientist Sue Clearwater, who has been leading Kakahi research for the last few years, said a University of Waikato doctoral student, Michele Melchior, had recently found a clue around how to help prevent the species decline.

Michele’s PhD study is part of the Cultural Keystone Species research programme, which is funded by the Ministry of Business, Innovation and Employment.

Michele has discovered that the different mussel species have different reproductive strategies and that the population of one species is declining faster than its counterparts.

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Dr Clearwater says, “This particular species can live a really long time – up to 50 years or more. But if they’re not reproducing enough young they’re not replacing themselves, so they slowly die out and become a geriatric population.”

Results of the NIWA research indicate that Kakahi reproduce by releasing clouds of larvae into the overlying stream water, then attach themselves to passing fish and “hitchhike” upstream to new habitat where they drop off, settle and grow. They transform from larvae into juvenile mussels during the hitchhiking phase.

Barriers to movement by the carrier fish, including poor water quality, reduce survival in the mussel populations.

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One of the Kakahi species, Echyridella aucklandica, releases larvae in a way that mimics fish food and lures suitable carrier fish close enough for the larvae to attach to the fish gills. Dr Clearwater says that this is the first report of freshwater mussels using fish-food mimicry outside of North America.

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“It provides us with another piece of the puzzle in the mussel lifecycle, and it points to what we need to do to conserve and restore the species,” said Clearwater.

Dr Clearwater admitted to developing a fondness for Kakahi, despite describing them as the “cabbage of the aquatic world” – okay to eat but probably not the most favoured of foods.

“There’s something quite primal about collecting nice big mussels from a stream, just like collecting tua tua at the beach. Also the adults can be old and tough, but the juveniles are highly sensitive to environmental changes. That’s what makes them so fascinating.”

Contact:
Dr Sue Clearwater,
Ecotoxicology Scientist.
https://www.niwa.co.nz/people/sue-clearwater 

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