Allison Cartwright is web publication officer for our Early Career Scientists (ECS) group. Here, she ponders the consequences of our appetite for crayfish and a cavalier attitude to pollution.
The white-clawed crayfish is an endangered species found in the UK and Ireland. Typical to many situations – mankind is to blame for their endangerment. We have destroyed the homes (rivers and lakes) of these little critters by changing rivers to suit our lifestyles or via reckless pollution.
The problem is compounded by our desire for big crayfish to eat, as this led to the introduction of large, non-native crayfish, such as the signal crayfish. This satisfies our hunger, because they contain lots of tasty meat, but the adopted crayfish carry diseases that are fatal to our little native crayfish. The worst of these diseases, is the crayfish plague, caused by a fungi-like organism (an oomycete) called Aphanomyces astaci.
There are five genotypes of A. astaci which can infect crayfish of many species. When the oomycete produces spores, they are attracted to the chitin that make up the crayfish’s body where they embed themselves and start to grow. They grow more and more until mycelium (root like structures) reach the nerve cord of the crayfish resulting in death.
Upon the demise of its host, the oomycete bursts the crayfish’s body open to release its spores and restart the cycle. The plague can be carried by non-native crayfish without always killing them. Like many pathogens, the plague relies on large non-native crayfish including the signal crayfish to act as its host.
War on the white-claw
When the crayfish plague is introduced (on non-native crayfish or on fishing gear) this kills every infected white-clawed crayfish in a wave of untimely death. This results in washed up dead bodies resembling those of a battlefield caused by an unwinnable war with microbes.
The oomycete causing the plague, like many pathogens, evolves with time. This means that we cannot eradicate it and prevents our crayfish from developing immunity (although a population of white-clawed crayfish in Spain is believed to be immune to the plague, but this requires confirmation).
Clawing back from the brink
What can we do if we don’t want our crayfish to join the dinosaurs? Well, a number of facilities and universities around the UK and Ireland have set up spaces to breed crayfish. These behave like many zoos with conservation aiming to increase their numbers and to educate.
After all, if we do not know about our crayfish, how are we meant to save them? I have been fortunate enough to help with the conservation of my favourite clawed creature for my master’s project.
If we want to safeguard their numbers, the first thing we must do is get them to breed (cue the music and turn down the lights). Once they have eggs, the next battle begins: a battle against microbes. Crayfish mothers keeps the eggs under their tail for the whole incubation (and for around two weeks when they hatch).
She folds her tail in around them to keep them nice and safe (particularly from other crayfish), not forgetting to occasionally open and close her tail repeatedly to bring fresh, clean water to her little eggs. But each pass of water brings new microorganisms, mainly fungi, which could infect her developing eggs.
Crayfish breeders fear fungi, an anxiety rooted in the basic biology of what fungi do: create spores to spread from one egg to another, or send out mycelium to attach to the neighbouring egg. Fungi can cause the total loss of the mother’s eggs; a nightmare for species conservationists!
Thankfully, nature has a solution. The crayfish mothers are clever little critters and they tend to their eggs, removing dead ones with a small claw-like structure at the end of each leg. This ideally stops the spread of natural fungi from one egg to the next.
I’m still amazed at how they know which eggs are dead, they do change colour, but the clever mother has usually removed the egg before the colour change, which is when I know it has died. Crayfish breeders have also developed their own methods for preventing fungal infections where we remove her eggs and incubate them artificially, treating them in salt water briefly (and regularly) to kill fungal spores. This does work, but to quote a popular phrase, I still think “mother knows best”.
Prevention is better than cure
Anti-fungal interventions are only an attempt to improve a dire situation. The best option would be to disinfect fishing gear before using it in other rivers and more importantly, stop the introduction of non-native organisms. Crayfish are seasoned escape artists and are known to walk over land to get around obstacles in streams, or to move between water bodies.
Fighting the crayfish plague requires a number of measures. Preventing fungi on crayfish eggs will continue to be a challenging mission. We can’t stop natural fungi and we’d be wrong to eradicate these microorganisms which are vital for nutrient recycling.
Allison Cartwright completed her undergraduate degree in Marine Science before carrying out a MRes studying freshwater crayfish at Ulster University, Northern Ireland. She’s remained at Ulster University and is currently a third year PhD student. Alison’s project combines environmental science and microbiology to study freshwater sponges in Ireland.
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