Phreatogammarus fragilis: The fragile well shrimp

By Waiology 06/12/2012 2

By Daniel Collins

Phreatogammarus fragilis is an endemic New Zealand crustacean that lives in aquifers. It is an amphipod (a relative of the sand hopper), and is one of the largest (commonly up to 25 mm excl. antennae) and strongest swimming of NZ’s stygofaunal* crustaceans. Because it is so rarely observed, it does not have a common name; the best translations are ‘fragile well shrimp’ or ‘fragile groundwater lobster’, ‘fragile’ probably because its appendages broke off when early specimens were being identified and preserved.

The individual below is a 12 mm-long female with a brood pouch beneath the abdomen. It is white and translucent because there is no point in investing in pigments if it’s too dark to see or if there’s no risk of sunburn. This individual was caught in a trap in a 6 m-deep well beside the Selwyn River in Canterbury by Nelson Bousted and identified by Graham Fenwick. It was photographed live in water in a custom-built aquarium with several off-camera flashes.

Photo credit: Nelson Boustead

Waiology will have some more in-depth science of stygofauna in a future post.

* Stygofauna: animals that live in groundwaters, named after the river in Greek mythology, the Styx, which separated the Earth from the Underworld.

Dr Daniel Collins is a hydrologist and water resources scientist at NIWA.

2 Responses to “Phreatogammarus fragilis: The fragile well shrimp”

  • Research on stygofauna is a whole new area of interest to groundwater hydrologists and their freshwater ecology colleagues.

    Interestingly at last week’s NZ Hydrological Society annual conference in Nelson, Peter Callander showed downhole video footage of the damage to some Christchurch wells from the earthquakes, and in the process captured excellent footage of an organism that looks like a stick insect swimming around within the well casing. Perhaps the first video footage of stygofauna in situ in NZ.

    Interesting to speculate about the potential cleansing function that stygofauna communities may play in NZ aquifers, removing pathogens and nutrients.

  • Yes, I know Murray Close is interested in the role of groundwater ecosystems (more so biofilms in the vicinity of point source pollutants I believe) as a means of ecological engineering. But I think we need to first characterise the ecology. Who lives there? Who eats whom or what? What are the spatial patterns of food and organisms, and their changes in time? What are the disturbances and energy limitations? And how do g/w ecosystems contrast with surface freshwater and with marine (near-surface and deep)? [DC]

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