“Tourists don’t pay to see a crab,” said Tatenda Dalu of the Department of Ecology and Resource Management at the University of Venda. “Charismatic animals – like the big five – tend to receive the focus of conservation activities due to the tourist dollars they attract. Often the vital ecological role of the smaller organisms is ignored – for example, dragon flies are now used as important water-quality indicators. We only notice when there’s a crisis – like currently with the bee population. Crabs, especially the freshwater varieties, – no one knows much about them and their important ecological role is therefore overlooked.”
Dalu, who is an Iso Lomso fellow at STIAS, is hoping to change that perspective by surveying the distribution and abundance of crab species Potamonautes spp. in the Eastern Highlands of Zimbabwe, as well as trying to understand their direct and indirect impact on community livelihoods, how these aspects impact on species preservation and to identify opportunities and constraints to crab conservation.
“Government agencies tend not to care as much about the smaller species. We are trying to highlight the importance of these species in the environment and within conservation action plans,” he said. “The study aims to lead to better formulation and implementation of conservation strategies that provide long-lasting conservation action plans.”
“The greatest impact is the human impact,” he continued. “Human population growth threatens the integrity of 0.8% of the earth’s freshwater ecosystems globally, through reduction of its ability to support biodiversity and provide ecosystem services.”
Potamonautes is the most widespread genus of African freshwater crabs.
“Within the last ten years 18 new species have been described taking the total to 33,” said Dalu. Included in this is one species identified by a team from Stellenbosch University that included Dalu.
“We know that they are massive ecosystem engineers and break down organic matter. We are also trying to understand their role and situation within the overall food web.”
Dalu’s study includes fieldwork in sites in Chimanimani and Chipinge. Parts of these areas also fall under the larger CAMPFIRE model – the Community Areas Management Programme for Indigenous Resources – which was started in the early 1990s with international funding and, besides conservation, also includes income-generation activities.
“CAMPFIRE mainly focuses on the larger animals but also indirectly protects some of the smaller species,” said Dalu. “It will be interesting to compare areas where CAMPFIRE operates versus areas where it doesn’t.”
The aim of the fieldwork is to understand the abundance of the different Potamonautesspecies in the area. Dalu is also conducting detailed interviews with community members about their practices concerning the crab species, their personal level of exploitation of the crabs and their willingness to participate in crab conservation.
“Local community involvement is key to the success of any crab-conservation activities,” he said. “I believe this socio-ecological information can feed into ecological and conservation strategies.”
“The biggest drivers of the abundance of the crabs seem to be the river bedrock, water quality, temperature and the presence of macrophytes.”
The threats include natural predators like large fish, birds and otters although Dalu pointed out that these are not found in large numbers in these areas. The more important threats seem to be humans via their use of the crabs as a food source, the use of fertilisers for small-scale agriculture alongside the riverbanks and, importantly, illegal gold mining.
“Where there are more people, there are less crabs,” said Dalu. “Also where there is more poverty there is greater crab consumption.”
“The frequency of crab harvesting differs significantly between households,” he said. “It’s important to understand in more detail how the community values the importance of the crabs as a source of nutrition. They may be the only food source in certain months especially during low crop yield seasons – luckily this doesn’t coincide with the crab-breeding season which occurs in December when the females can produce several hundred offspring.”
“However, one of the biggest threats is the illegal gold mining in these areas which diverts the streams and also adds toxic substances like mercury to the water. Areas with serious goldmining activities have less or no crabs.”
In discussion, Dalu highlighted the inevitable trade-off for the community between mining and harvesting crabs for food.
“From the interviews it appears that only a small number of the miners come from the actual community,” he said, “but, of course, it’s an illegal activity so they may not admit to involvement.”
It’s also a dangerous activity with the involvement of government officials and powerful individuals, contestation around the ownership of natural resources and the potential threat of violence to locals.
“What is clear is that where there is money to be made from mining – ecology comes second best,” said Dalu.
“And, of course, what is fascinating is to consider is how a local ecological challenge cannot be divorced from the larger global economic and political conversation.”
Michelle Galloway: Part-time media officer at STIAS
Photograph: Christoff Pauw