- An unusual invasive crayfish has been spreading in Madagascar, threatening aquatic biodiversity even as it helps nourish the country’s food-insecure population.
- The marbled crayfish (Procambarus virginalis) evolved only in recent decades as part of the German aquarium trade. It’s entirely female and reproduces clonally without males.
- Ranja Andriantsoa, a Malagasy biologist and epigenetics researcher, began studying marbled crayfish as a way to learn about cancerous tumors, which reproduce in a similar way.
- Andriantsoa’s ongoing research focuses on the social and health impacts of the marbled crayfish and aims to inform Madagascar’s strategy for managing the crayfish’s ecological impact.
In 2005, farmers in Antananarivo discovered an unfamiliar creature in their rice paddies. It was a crayfish unlike any other in Madagascar, and it soon spread throughout the country’s central highlands.
When a team of researchers at the German Cancer Research Center in Heidelberg sequenced its genome a decade later, they confirmed that it was an entirely new species, and, remarkably, one that had evolved within the past 30 years. Somehow, a mutation in crayfish kept by aquarium breeders in Germany had produced all-female offspring that were clones of the mother, capable of reproducing without males. This rare ability occurs in roughly one out of every 1,000 vertebrate species; it’s even rarer for it to be the only way a species procreates, as is the case for marbled crayfish (Procambarus virginalis).
Malagasy biologist Ranja Andriantsoa was part of that research team, which began studying the marbled crayfish as a way to learn about cancerous tumors. Like cancer cells, marbled crayfish are highly adaptable, they grow quickly, and each generation is genetically identical to the last.
In Madagascar, the crayfish’s rapid spread drove fears that it would damage delicate aquatic ecosystems, even as locals came to rely on it as an abundant and affordable source of protein. Fifteen years on, this combination of usefulness and threat has led to a kind of national ambivalence around how Madagascar should approach managing the marbled crayfish.
Andriantsoa’s ongoing research, primarily in partnership with Julia P.G. Jones of Bangor University in the U.K., focuses on the social and health impacts of the marbled crayfish. She says the research will ultimately help inform the national strategy for managing the crayfish’s ecological impact too. After all, Madagascar is a country where understanding interactions between people and wildlife is especially important in conservation because the immediate needs of the growing human population often seem at odds with the preservation of its singular biodiversity and landscapes.
Mongabay supported Rowan Moore Gerety’s reporting in Madagascar for a long feature about the marbled crayfish published in the latest issue of Harper’s Magazine, called “Stowaways: Madagascar reckons with an invasive crayfish.” What follows are excerpts of an interview he conducted with Andriantsoa that have been condensed and edited for clarity.
Mongabay: What is the marbled crayfish and where did it come from?
Ranja Andriantsoa: Marbled crayfish is a small freshwater crayfish (average size of 4-6 cm, or 2-3 inches, and maximum size of 10-12 cm, or 4-5 inches) from the genus Procambarus. It was first discovered around the mid-1990s in the German aquarium trade. It’s a very special animal because it has recently evolved from a mother species, Procambarus fallax, which is from Florida. The main characteristic of this species I would say is its reproduction mode. So, it’s a female species that reproduces by parthenogenesis, which basically means that they reproduce by cloning. So the offspring are exact clones of the mom in terms of genetic material. It has spread over Europe through the aquarium trade, and established a wild population in Madagascar as well.
The marbled crayfish is now very widespread in Madagascar: what makes it unique as an invasive species?
As an invasive species, the marbled crayfish possesses the attributes of an invader, mainly illustrated by its ability to adapt to different ecosystems.
What makes the marbled crayfish a unique invasive species is the extra feature that other invaders do not have. Genetic diversity is one of the key features that allows adaptation to new environments. But marbled crayfish — whether they are found in Germany, Romania, Malta or Madagascar — are all genetically identical. This is possible because their reproduction mode, parthenogenesis, generates an all-female population: each egg an individual female lays carries genetic material that allows it to develop into an adult and reproduce again without any male intervention.
After it was first recorded in Madagascar around 2005, the marbled crayfish increased its distribution area over 100-fold in about 10 years. One animal can potentially raise a new population. Hence, the marbled crayfish displays a very unique and impressive invasion process on an island with rich biodiversity.
What do we know about its effects on native wildlife, particularly Astacoides, the genus of crayfish found in the mountains in southeastern Madagascar?
Although invasive alien species are considered to be one of the major drivers of biodiversity loss, and all seven species from the genus Astacoides are endemic to Madagascar, we still do not have any information regarding the potential impacts of marbled crayfish on Astacoides species.
What is known so far is that their habitats overlap in one area at the edge of the rainforests of Ranomafana National Park in southeastern Madagascar. In fact, two habitats were found holding natural populations of both Astacoides species and invasive marbled crayfish.
This lack of information on the potential effects of marbled crayfish on native wildlife might be due to the fact that marbled crayfish, unlike many other invasive species, is mostly found in populated urban and rural areas. Nonetheless, as an invasive freshwater species, its presence is an additional pressure on the native aquatic biodiversity. So it is essential to assess the impacts of invasive marbled crayfish both on native crayfish and on other native fauna and flora.
Your current research also focuses on the socioeconomic impacts of marbled crayfish in Madagascar. What made you interested in researching that issue specifically? What have you learned?
In the beginning, marbled crayfish wasn’t seen as a good food source because it was found in an unhealthy environment so people associated it with unhealthy food. [Editor’s note: It was initially found in polluted canals and wetlands in the capital city, Antananarivo.] The more it spread over Madagascar, the more that perception changed. Over time, people found out it’s edible, and started to consume the marbled crayfish.
And it’s easy to collect. Compared to fish, or other aquatic food sources, the marbled crayfish is one of the species that’s super-easy to catch. [People collect them by walking through wetlands and rice paddies where the crayfish are abundant and picking them up with nets.] Economically speaking, you don’t have to pay to eat crayfish, or you can collect it and then sell it. That’s one of the findings we had from our last paper, that compared to a set of other proteins, the marbled crayfish, especially when it’s sold alive, is the cheapest source of protein that could be found in the markets.
An invasive species is expected to have negative impacts on biodiversity when it invades a new environment or ecosystem. But in order to make proper decisions on conservation, we can’t only focus on biodiversity, or biological and ecological impacts. We have to see the impact on sustainable development. The human component can be a very important factor that can either improve the conservation strategy that we would choose, or [show that it might not work]. That is one of the reasons the economic and social aspect of the marbled crayfish is something we are studying now.
People in Madagascar agree that marbled crayfish is there to stay, and it’s a widespread food source in a food-insecure country. But there are also worries about its effect on rice cultivation and fishing. Can you explain them?
When the species was not identified yet, there were awareness campaigns done in Madagascar, in 2009-2010, to inform people that marbled crayfish can have potential negative impacts on rice production. [There was evidence from around the world that similar species feed on rice plants and create burrows in the ground that interfere with irrigation. Indeed, Malagasy farmers have since reported similar behaviors by marbled crayfish.] So this was of course shared through the media — on TV and on the radio, but word of mouth, too — and of course, information changes when it goes from one person to another. Also, Malagasy fishermen and people with rice fields have firsthand information that marbled crayfish can kill part of their rice crop, or predate on the fish or the fish eggs that they catch. A few studies have been done, though they’re not yet published, so we have basically no data on marbled crayfish and the impacts on agriculture in Madagascar.
There’s a lot of stigma associated with eating marbled crayfish. Help us understand that stigma, its origins, and the way it spreads.
Newspapers and word of mouth have led the population to misinformation. The marbled crayfish’s ability to survive in multiple habitats has led them to invade polluted water bodies, though they have also spread to clean environments. This adaptation to polluted environments has given them this label of a “dirty” animal associated with unhealthy food.
The cheap price of the marbled crayfish on the market, and free access to crayfish in lakes and rice fields has let people label them as the poor people’s food. There is no data supporting the idea that wealthy people do not consume marbled crayfish.
In addition, there are health issues experienced by consumers, like crustacean allergies or stomach pain that may be associated with eating the whole animal with the shell.
There are signs, though, that the status of marbled crayfish has changed over time. The evolution in food processing — pre-cooked crayfish tail-meat is now sold on the market, or in prepared meals and snacks — and the increasing awareness that marbled crayfish can be collected in clean environments may be contributing to a change in perception.
All images taken in 2019 by Rowan Moore Gerety for Mongabay.
At the government level, stigma seems to have made it harder to act. What might a national strategy around marbled crayfish look like — both to study any ecological and agricultural damage from crayfish and to try and harness any benefits a crayfish industry might bring?
This is one of the hardest questions you’ve asked: I would say basic research is the first step we have to take. Because, literally, we know next to nothing, and we can’t have a strategy if we don’t have information. On the ecological side, we can follow standardized protocols to study the impacts, but on the agricultural side, it’s more complicated. That’s something where proper researchers in that field could really help.
We know the marbled crayfish is established, and it won’t leave. Now the balance is to try to control the spread, and see if it really has important consequences on native biodiversity. When you think about invasive alien species, you think about the negative impact, but marbled crayfish are one of these species that is edible, unlike other species. So managing the species on the national level should really take into account all the pluses and minuses. The challenge would be: limit spread, limit impacts on biodiversity, but use it where possible.
First, we need to learn what’s going on right now: How does the current market for the marbled crayfish work? How the product is transformed, how it’s shipped, which areas are involved in the marbled crayfish trade. Where are the producers? Consumers? And from the very, very start of the supply chain, how do people farm the marbled crayfish? Do they even farm it? Do they have special infrastructure or do they just collect it? We need to have an understanding of the state of the market.
The coronavirus pandemic has slowed research across the world, but you’re still working on a couple of projects on marbled crayfish in Madagascar. What are the research questions you’re pursuing now?
My previous work studied two very different aspects of marbled crayfish leading to the same goal: improving human health. First, I studied epigenetic mechanisms in the marbled crayfish in order to provide data that could help establish the marbled crayfish as a model organism in medical research, including cancer research. I also studied the marbled crayfish’s potential as a complementary method to control neglected tropical diseases in developing countries. I performed the first predation experiment of marbled crayfish on Biomphalaria snails, intermediate hosts of the parasites that cause schistosomiasis, the second-deadliest parasitic disease after malaria.
My research is now focused on potential advantages of the invasive marbled crayfish for human health. First, as a potential predator of snails that are intermediate hosts of schistosomiasis disease. We know their distributions overlap, but we are now exploring to what extent they share the same habitat. I’m also studying how it could be a protein source to improve children’s health. Marbled crayfish is one of these invasive alien species that is also consumable. So, we aim to assess and understand the role that marbled crayfish can play to improve children’s protein intake.
Banner image: Cooked marbled crayfish are typically sold by the “kapoka,” or condensed-milk can. Image by Rowan Moore Gerety for Mongabay.
Rowan Moore Gerety is a journalist in Phoenix and the author of Go Tell the Crocodiles: Chasing Prosperity in Mozambique.
Citations:
Gutekunst, J., Andriantsoa, R., Falckenhayn, C., Hanna, K., Stein, W., Rasamy, J., & Lyko, F. (2018). Clonal genome evolution and rapid invasive spread of the marbled crayfish. Nature Ecology & Evolution, 2(3), 567-573. doi:10.1038/s41559-018-0467-9
Andriantsoa, R., Jones, J. P., Achimescu, V., Randrianarison, H., Raselimanana, M., Andriatsitohaina, M., … Lyko, F. (2020). Perceived socio-economic impacts of the marbled crayfish invasion in Madagascar. PLOS ONE, 15(4), e0231773. doi:10.1371/journal.pone.0231773
Jones, J. P., Rasamy, J. R., Harvey, A., Toon, A., Oidtmann, B., Randrianarison, M. H., … Ravoahangimalala, O. R. (2009). The perfect invader: a parthenogenic crayfish poses a new threat to Madagascar’s freshwater biodiversity. Biological Invasions, 11(6), 1475-1482. doi:10.1007/s10530-008-9334-y
FEEDBACK: Use this form to send a message to the editor of this post. If you want to post a public comment, you can do that at the bottom of the page.
Credits
