Kākahi - Freshwater Mussels

Freshwater mussels, known as Kākahi in New Zealand, are one of the most imperiled organisms on Earth and populations are declining globally with 70 percent of species considered at risk or threatened. This is including three species endemic to New Zealand. Echyridella menziesii is classified as declining, Echyridella aucklandica is considered nationally vulnerable, and Echyridella onekaka is naturally uncommon. These species are often geographically isolated and can only be found in a few locations which means they are likely to continue their decline if nothing is done to address the cause behind this imminent extinction.

Mussels are an important part of a lake ecosystem; as biofilters and bioturbators they filter out nutrients, algae, bacteria, and fine organic material which helps purify the water. They have the capacity to filter up to one liter per hour, and if present in large enough numbers, they can filter the entire volume of a small lake within days. They also oxygenate the sediment by moving it around which decreases anoxia and stems sediment nutrient remobilization. Aside from their ecological importance, these mussels were once a mahinga kai resource for many Māori, the shells were used as cutting utensils and to feed sick or abandoned infants.

Freshwater mussel population decline worldwide have been attributed to the loss of habitat associated with eutrophication and sedimentation as well as pollution. In Lake Rototoa (one of our project sites), the loss of native intermediate host fish through predation from invasive species is a significant contributor to their reduction in numbers. Unlike their marine counterparts, freshwater mussels cannot anchor themselves to a substrate. Instead, they bury themselves into the sediment which makes them vulnerable to increased sedimentation that can result from erosion in the catchment as well as from excessive organic matter like algal blooms. The fine silt clogs up their gills and suffocates them, leading to the death of many individuals. Aotearoa Lakes goal is to continue researching these vulnerable species to try and halt there decline.

 

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