signal crayfish – More Than A Dodo

Crayfish of the world united

by Sammy De Grave, head of research

How many species of crayfish can you name? Not many, or perhaps none? Well today, for the first time, a list of all the species of crayfish in the world has been published, thanks to a collaborative effort between Professor Keith Crandall at George Washington University and Dr Sammy De Grave, head of research here at the Museum.

The new list draws together much recent work and gives biologists access to a single, comprehensive summary of all the recognised species of crayfish for the first time. The new classifications group crayfish into 669 species, 38 genera, and five families, with two superfamilies corresponding to the Northern and Southern hemispheres.

*Fallicambarus devastator.* Image: Chris Lukhaup

On the occasion of this taxonomic triumph it seems like a good opportunity to take a look at some interesting crayfish from around the world.

Outside biological taxonomy, crayfish are much better known as a source of food. They are eaten worldwide, but especially in the southern US, Australia, and Europe, where the Red Swamp Crayfish (Procambarus clarkii) is most commonly on the menu. As a result, the Red Swamp Crayfish has been introduced into several countries and has out-competed the local species.

Several other species are also known as invaders. The Signal Crayfish (Pacifastacus leniusculus), native to North America, is now very abundant in Europe, and is out-competing the native Noble Crayfish (Astacus astacus).

The Noble Crayfish (*Astacus astacus*), above, is native to Europe, but is being out-competed by the introduced Signal Crayfish (*Pacifastacus leniusculus)*. Image: Chris Lukhaup

Another remarkable crayfish is the Marmorkrebs, a species which still has no official taxonomic name. It was first noticed in the aquarium trade in Germany in the 1990s, but no natural populations are known. But the really interesting thing about this species is that all known individuals are female: it is parthenogenetic, which means the females reproduce from eggs without fertilisation – no males involved!

The Marmorkrebs crayfish has no official taxonomic name and is parthenogenetic – all individuals are female, genetically identical and reproduce without males. Image: Chris Lukhaup

Unfortunately, Marmorkrebs has escaped from aquaria in several countries, and is outcompeting local species due to its fast reproduction. Of most concern is its occurrence in Madagascar, where it competes for food and space with the endemic Astacoides crayfish, a much larger but slower-growing species.

*Astacopsis madagascariensi*, above, is being out-competed in Madagascar by the Marmorkrebs, which has escaped from several aquaria. Image: Chris Lukhaup

The Tasmanian Giant Crayfish (Astacopsis gouldi) is considered to be the largest freshwater invertebrate on the globe. Although its size has declined in recent years due to over fishing, historical specimens weighed up to 6kg and could reach 80-90 cm in length.

The completion of the new world crayfish list allows for further refinements to the conservation status of the animals too. Current Red List assessments show that 32 per cent of crayfish are already thought to be threatened with extinction, a similar number to freshwater shrimps and crabs.

It is really exciting to finally have a single source for the world’s freshwater crayfish taxonomy. Such a resource will impact a wide variety of fields that rely on crayfishes as study organisms. We hope it will also advance conservation efforts of these keystone species of highly endangered freshwater ecosystems.
– Professor Keith Crandall, George Washington University

The paper, An updated classification of the freshwater crayfishes (Decapoda: Astacidea) of the world, with a complete species list, is published today in the Journal of Crustacean Biology.

Invasive crayfish

A Spotlight Specimens special for Oxford Festival of Nature

By Sancia van der Meij, Research Fellow

The White-Clawed Crayfish (Austropotamobius pallipes) is often assumed to be native in the UK, but was in fact brought across by monks in the Middle Ages from northern France

In the 1970s this was joined by a further seven invasive crayfish species from other parts of the world, but mainly from North America. Some of these species have a very restricted distribution in the UK, such as Procambarus acutus which is only known from a single pond in Windsor.

The most widespread of these is the Signal Crayfish, Pacifastacus leniusculus, which was introduced to Europe in the 1960s and reached the UK by 1975. It is now widespread in waterways around England, Wales and parts of Scotland. There are records of Signal Crayfish from all over Oxfordshire, in the River Thames, River Cherwell, canals and ponds, and they are fished for by many people as sport or food.

The Signal Crayfish is so named because of the blue-white patches on the underside of its claws, next to the finger joint. It is the easiest invasive species to identify given its large size, smooth carapace and signal spots.

The Red Swamp Crayfish (Procambarus clarkii), from North America, is an invasive species in the UK — The Red Swamp Crayfish (*Procambarus clarkii*), from North America, is an invasive species in the UK

There are a number of information sites to help with identification such as the UK Crayfish Hub run by Buglife. The Non-Native species website runs a recording scheme for sightings of all invasive species too. Don’t worry though, the huge Tasmanian Giant Crayfish (Astacopsis gouldi) shown in the video clip has not made it to our waterways!

Whilst increased levels of water pollution and habitat degradation, fragmentation and loss have played their part in the decline of many crayfish populations, several species are also significantly impacted by the introduction and spread of a disease known as ‘crayfish plague’, a fungal disease is carried by some North American species.