The recent discovery of Killer Shrimps (Dikerogammarus villosus) in an English reservoir (cambridge news) is yet one more example of the way in which human activities are influencing the natural world. As these shrimps take over in new environments they disrupt ecosystems.
Invasive Species
It is quite natural for successful animal species to expand their range – this is one of the ways in which evolution works (for example the way in which North American animals moved south in the distant past and altered the ecosystems in South America). The problem nowadays is that humans are responsible for transporting many animals into new environments (often new continents) at a rate that is just too fast for natural ecosystems to adapt. A few examples here should make the case:
- Fishermen in America can inadvertently release European earthworms into remote locations – these new worms often change the nature of the soil, killing off natural vegetation and all the animals adapted to live there. (European earthworms might well be a factor in the decline of the Palouse Giant Earthworm.)
- Animals used for research and educational purposes can sometimes escape, and as with the African Clawed Frog they can be responsible (indirectly in this case) for damage to wild animals. African Clawed Frogs are thought to be at least partly responsible for the alarming spread of fungal disease (chytridiomycosis) that is killing amphibians all over the world. Even the seemingly harmless laboratory stick insect has the potential to cause damage!
- Deliberate introduction of foreign species, in attempts to effect biological control of pests, can often go wrong. The Cane Toad in Australia is a good example, and even ladybirds (ladybugs) can cause problems – the 'Harlequin' is responsible for the decline of hundreds of ladybird species in America, and many in the UK.
Killer Shrimps
Dikerogammarus villosus was originally native to rivers in the Black Sea and Caspian Sea drainage basins (Eastern Europe), but the opening of a canal linking these waters to others in central and western Europe allowed it to expand its range dramatically. Killer shrimps can now be found in most European rivers. How it spread across the sea to England is unknown, but it is certainly in Grafham Water.
Killer Shrimps are actually freshwater amphipods, but they are omnivorous and unusually aggressive (for an amphipod!). They kill and eat other amphipods and a wide range of other freshwater invertebrates (damselfly nymphs, water hoglice, and water boatman, for example). They will even eat young fish.
Killer Shrimps are tougher than the average amphipod, coping with a wide range of water temperatures (0–30 °C), low oxygen levels, and even mild salinity.
The Killer Shrimp can be bad enough on its own, but when it teams up with another invasive species (the Zebra Mussel) it can take over environments at an alarming rate.
Zebra Mussels and Killer Shrimps
The Zebra Mussel (Dreissena polymorpha) was originally restricted to Russia, but can now be found in many parts of the world. As it feeds it throws out debris that Killer Shrimps love to feed on, so when the two species are present together at the same location the population of Killer Shrimps can explode.
Killer Shrimps and Zebra Mussels are just two examples of invasive species that can cause immense environmental damage.
Reference:
'Reservoir alert over killer shrimps' - cambridge news, 2010.
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