This cache has been placed to raise awareness of our native freshwater fish/Invertabrate species. Over time I will add more caches in the Wanganui Region with the same theme. Native fish are something I have great interest in, and was one of my hobbies before I was engulfed in this Geocaching thing ;-)
Common name: Freshwater mussel
Scientific name: Echyridella menziesi
About this species
Freshwater mussels are under threat and are declining, both in New Zealand and worldwide. This decline has been attributed to the loss of habitat associated with river regulation, eutrophication, and other types of pollution, and possibly through loss of the host fish on which completion of the life cycle depends.
Kākahi are common and widespread throughout New Zealand, in habitats ranging from small, fast-flowing streams to lakes.
Impacts on kākahi
No single impacting factor has been identified as being consistently important to the decline of kākahi. Modifications to, or destruction of habitat (e.g., river regulation, eutrophication, sediment type, water quality, water velocity, the degree of sedimentation, and the angle or slope of a lake or river bed) are likely to be key drivers of this decline, affecting adult populations as well as host fish species which are essential for completion of the kākahi life cycle.
While the kākahi or freshwater mussel may look humble, it has some pretty interesting life history traits. While most mussels expel eggs and sperm for external fertilisation in the water, a mother kākahi keeps her eggs inside her shell to develop.
She takes in sperm through her inhalant siphon and her eggs (thus fertilised), are then held internally, in brood chambers until they develop into larvae called glochidia. These glochidia (about the size of a grain of sand) are then ‘sneezed’ out of their mother’s exhalent siphon, whereupon they latch onto a passing native fish’s gills to spend the next stage of their life cycle as parasites! A developmental strategy like this provides a useful means of dispersal for kākahi—allowing population growth, while avoiding overcrowding. The presence and abundance of the original fish host (kōaro) of kākahi, that carries the parasitic larval stage (the glochidia), may have impacted on kākahi numbers.
Kākahi are amazingly long-lived—age estimations have included individuals over 50 years old. The future for this species is uncertain, as juveniles currently seem to be either absent or very rare in many populations studied. Like most freshwater mussels, kākahi are thought to be very sensitive to ammonia, which enters waterways through municipal wastewater discharges and through the inputs of nitrogenous wastes from animals. Hosts for kākahi larvae are also a lot harder to find, as so many of our indigenous freshwater fish species are declining.
To date there has been limited research undertaken in New Zealand investigating key drivers influencing presence, distribution, and density of freshwater mussels in lakes.