Farewell to a native species dying in the lake?
By Martin Freeth
Freshwater kākahi – native mussels once a key food source in Lake Wairarapa – face potential extinction as they pay the cost of urban discharges and farm run-off.
Lake Wairarapa’s supertrophic water quality is pushing kākahi towards extinction and the ecologic future of the lake and its precious wetlands is highly uncertain despite the efforts of various stakeholders.
(Supertrophic: a trophic level greater than 5 means water quality is rated “very poor.” Lake Wairarapa is saturated in phosphorus and nitrogen and has poor water clarity. It has been officially classified as supertrophic since 2012).
Kahungunu Iwi, the lake’s kaitiaki/guardians, told The Star earlier this year that “the lake is dying.”
Urban discharges and farm run-off have long been recognised as causing serious decline in the water quality of Wairarapa Moana – the North Island’s third-largest freshwater body and part of the globally-recognised Wairarapa Moana lakes, wetland and river environment.
The science-based, official LAWA (Land, Air, Water Aotearoa) website records Lake Wairarapa as supertrophic because of its persistent high nitrate and phosphate readings, and levels of algae and sediment.
There’s been little change since water quality monitoring started in 1994 – despite a Water Conservation Order placed on the lake for its ecological value and despite a 2020 declaration of
Wairarapa Moana’s international importance under the Ramsar (UN) Convention on wetlands.
Kākahi are a key bioindicator of ecological health and the plight of this species is highlighted in a new research report from NIWA marine and freshwater ecologist Mark Fenwick after 10 years’ systematic monitoring at two Lake Wairarapa sites.
The research has shown relative abundance of older kākahi but their growth is slow and there’s an almost complete lack of juveniles in the monitored populations.
“It is possible that the effort required by adults to extract food from the sediment rich water leaves them without the necessary strength for growth and reproduction,” Fenwick said in a report. … Continue Reading
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