Aussie inverts desperately in need of a bit of protection
When Thomas Huxley – Darwin’s ‘bulldog’ and greatest advocate – searched for an animal on which to base his Introduction to Zoology (1880), he naturally settled on the humble crayfish. In his own words, he wanted to show how “the careful study of one of the commonest and insignificant of animals, leads us […] to the widest generalisations and the most difficult problems of zoology”. Unfortunately, he completely ignored one of the richest countries in freshwater crayfish – Australia.
Home to 148 of the 600 species recognised globally, Australia is a heavy weight of crustacean diversity. This includes the world’s largest freshwater invertebrate – the Tasmanian giant Astacopsis gouldi, weighing in at a whopping 5 kg – and some of the smallest species, measuring barely 1 cm. Not only are Aussie crayfish species numerous and diverse, they are evolutionary relicts. They diversified around 150 million years ago – the same age as the global radiation of birds.
Australian crayfish drifted away from their South American and Malagasy cousins during the split of the Gondwanan supercontinent. Isolated on a continent with extremely variable water availability, they slowly evolved to fill a number of niches. Some crayfish live exclusively in fresh waters, some live in temporary desert springs, whilst others dig burrows to access the water table. These extensive galleries would often fall under the weight of cattle and horses in the 19th century, so parts of eastern Victoria were renamed ‘crabhole country’. Problems of land subsidence decreased as crayfish went locally extinct due to damaging farming practices.
The global IUCN assessment recently revealed the dire condition of Australian crayfish – 66 species are threatened with extinction (Richman et al. 2015). The proportion of threatened species in some genera is extremely high: more than 80% in the spiny crayfish species (Euastacus spp.), and three out of five burrowing species from Western Australia (Engaewa spp.). Yet local conservation measures are lagging behind the global recognition of the threatened status of crayfish. Only 11 species are included on the EPBC act, leaving dozens of species in urgent need of listing (consider Figure 1).
Australian species are affected by a wide range of interacting threats. They suffer from the loss of riparian vegetation, invasive species (cane toads and other crayfish), and the deposition of nutrients, mercury and sediments in waterways. Climate change is an emerging though poorly-understood threat (see the box ‘How will climate change affect Australian crayfish?’). This means that crayfish populations are likely to decline further if threats remain unabated.
So, what can be done? The good news is that crayfish are well-known invertebrates: there is considerable ecological data, a complete phylogeny (Owen et al. 2015), and all species are mapped within their IUCN assessment. Further work in Australia could leverage the international interest triggered by the global assessment as well as help build national capacity. Many university departments focus on fish and crayfish biology, and crayfish enthusiasts (‘astacologists’) are very knowledgeable and passionate. Crayfish are appreciated by the general public, both as pets and as delicious sandwich fillings – the economic value of crayfish farming is estimated at 20 million dollars. Crayfish therefore have the capacity to become flagship species for the conservation of freshwater invertebrates.
“Crayfish may be the first on the line when it comes to climate change, and forty species have been identified as potentially sensitive to climate change by the IUCN.”
Key research and conservation questions will need to be answered to move crayfish conservation forwards. This includes transferring knowledge from well-known to poorly-known species; testing the efficacy of conservation measures (such as revegetation of riparian areas); and developing guidelines on captive breeding and translocation.
The process of listing crayfish under the EPBC Act also needs to be enhanced – especially for crayfish which live in flowing water, which remain largely underrepresented on the list (3 out of 11 species). Maintaining up-to-date recovery plans and conservation advice is also a challenge due to the lack of ongoing monitoring.
CEED researcher Lucie Bland is leading a global study on the factors predisposing crayfish to high extinction risk, and a global study on assessing crayfish vulnerability to climate change (following the framework proposed by Foden et al, 2013). She hopes that large-scale ecological information will help inform research priorities within Australia, and identify transferable conservation methods from other continents.
How will climate change affect Australian crayfish?
Crayfish may be the first on the line when it comes to climate change, and forty species have been identified as potentially sensitive to climate change by the IUCN. The effects of climate change on crayfish are likely to vary among species, and may be enhanced by other threats. For example, crayfish experience mass mortality during droughts and floods, when they are stranded on river banks to be snatched by collectors and cane toads.
Most spiny crayfish are mountain-top endemics, so their habitats may become unsuitable under climate change. In lowlands, the disappearance of riparian vegetation is likely to deprive crayfish from cool microhabitats. Burrowing crayfish may need to burrow further to track low water tables, and may not be able to disperse across agricultural landscapes. Finally, invasive crayfish adapted to warm waters may spread more widely, as has already been witnessed in Europe.
The effects of climate change are very difficult to predict as there is little information on individual crayfish species. Thermal sensitivity experiments have only been conducted on two species, so more lab and field studies are desperately needed. Progress also needs to be made in modelling the effects of climate change as most tools are adapted to data-rich, terrestrial species.
More info: Lucie Bland firstname.lastname@example.org
Foden WB, SHM Butchart, SN Stuart, et al. (2013). Identifying the World’s Most Climate Change Vulnerable Species: A Systematic Trait-Based Assessment of all Birds, Amphibians and Corals. PLoS ONE 8:e65427.
Owen CL, et al. (2015). A synthetic phylogeny of freshwater crayfish: insights for conservation. Philosophical Transactions of the Royal Society B: Biological Sciences 370: 1662
Richman NI, M Böhm, SB Adams et al (2015). Multiple drivers of decline in the global status of freshwater crayfish (Decapoda: Astacidea). Philosophical Transactions of the Royal Society B: Biological Sciences 370:1662