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Manx Rivers provide new home for North American Freshwater Shrimps – DNA tests provide clues to origin 14 December 2007

A tiny North American shrimp invader is alive and well and thriving in some Manx rivers. However, unlike troublesome invaders like Giant Hogweed and Japanese Knotweed, the impacts of this new invader on Manx river life may be minimal. Indeed, it may even be beneficial as it provides more food to the Island’s fish and ducks.

Elise Heinz, a scientist from Middlesex University visited the Island this week to track down populations of a river shrimp (*), aided by Dr. Calum MacNeil of the Isle of Man’s Government Laboratory, who has previously studied this invader in Northern Ireland. This pea-sized freshwater shrimp, which was first recorded in the Isle of Man just over 10 years ago, has also previously invaded rivers in England, Wales, Scotland and the Republic of Ireland, and was probably introduced into these areas by accident, with imported pond plants for garden centres. This is also probably how it got across to the Isle of Man. It can also hitch a ride on the feathers and feet of birds such as ducks and geese and so the shrimp has the potential to spread far and wide very quickly.

This shrimp lives in those parts of rivers or ponds too polluted or too low in oxygen for many other animals, including our native freshwater shrimps, which will catch and eat the invader shrimp in cleaner waters. It is also feeds mainly on decaying plant material and does not eat other shrimps or insects. It is only half the size of our native freshwater shrimp and walks uupright, unlike our native shrimps who move along on their sides.

In Northern Ireland, where it is present in many rivers, many studies have indicated that it is probably beneficial to fish populations of brown trout, minnows and stickleback, as it provides a good reliable food source for small fish and also for bigger insects that these fish also feed on. It also probably provides an additional food for the Island’s bird life.

Dr. MacNeil had previously found several rivers in the south of the Island with this shrimp, and suspected that it was probably more widespread and this week has indeed found it in even more sites. Elize Heinz has taken samples of these shrimps to examine their DNA to trace their most probable source. The spread and success of this shrimp and others like it, has been linked to climate change as it has been shown to be hardier than native shrimps, when it comes to things like rapid changes in water temperature.

* Latin name – Crangonyx pseudogracilis

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