Ecological Assessment of Two Species of Potamonautid Freshwater Crabs from the Eastern Highlands of Zimbabwe, with Implications for Their Conservation.

Tatenda Dalu,Ryan J Wasserman,Timothy Dube,William P Froneman,Mhairi E Alexander,Onias Bepe,Mwazvita T B Sachikonye,Kwanele I Manungo,Peter Alan Todd

doi:10.1371/journal.pone.0145923

Abstract

The spatial ecology of freshwater crabs and their conservation status is largely understudied in Africa. An ecological assessment was conducted at 104 localities in 51 rivers and/or streams in the Eastern Highlands of Zimbabwe whereby the distribution and abundances of freshwater crab species were mapped and the possible drivers of the observed trends in population structure explored. In addition, information on crab utilisation as a food resource by local communities was assessed via face to face interviews across the region. Finally, the conservation status of each species was assessed using the IUCN Red List criteria. Only two crab species Potamonautes mutareensis and Potamonautes unispinus were recorded within the region of study. Potamonautes mutareensis was largely restricted to less impacted environments in the high mountainous river system, whereas P. unispinus was found in low laying areas. In stretches of river where both species were found to co-occur, the species were never sampled from the same site, with P. mutareensis occurring in shallower, faster flowing environments and P. unispinus in deeper, slow flowing sites. Interview results revealed that the local communities, particularly in the southern part of the Eastern Highlands around the Chipinge area, had a considerable level of utilisation (55% of households) on the harvesting of crabs for household consumption during the non-agricultural season (May to September). Results from the IUCN Red List assessment indicate that both species should be considered as “Least Concern”. Threats to freshwater crabs in the Eastern Highlands, however, include widespread anthropogenic impacts such as habitat destruction associated with gold and diamond mining, inorganic and organic pollution and possibly exploitation for human consumption. The current study provides important information and insight towards the possible development of a freshwater crab conservation action plan within the region.

Highlights

The ecological role of freshwater crabs is often overlooked in aquatic ecosystems, despite their wide distribution in tropical and warm temperate zones [1]
In the southern African region, some twenty-five species of freshwater crabs belonging to the genus Potamonautes MacLeay 1838 are known to occur and there is a strong likelihood that the number of species will increase as taxonomy progresses and exploration continues in this relatively understudied field [13, 15]
Of the thirteen remaining variables, the abundance of both Potamonautes unispinus and Potamonautes mutareensis across the three regions was found to be significantly associated with conductivity, clay and macrophyte presence (Table 2)

Summary

Introduction

The ecological role of freshwater crabs is often overlooked in aquatic ecosystems, despite their wide distribution in tropical and warm temperate zones [1]. Crabs are important prey items, forming the intermediary trophic link between detritus and predacious animals such as fish, otters, mongoose and birds [4,5,6,7] Given their contribution to invertebrate biomass and their importance as prey items, freshwater crabs constitute an integral component of food webs in freshwater aquatic ecosystems [1, 4]. Freshwater crabs are present in almost all freshwater habitats, from mountain streams to large lowland rivers and small water bodies, often constituting the largest invertebrate biomass [3, 10,11,12,13,14,15,16] Owing to their generally limited dispersal abilities, most true freshwater taxa are endemic to certain ecoregions [4, 17,18,19]. Potamonautes belongs to the Potamonautidae, a family endemic to the Afro-tropical region [4, 10, 17]

Methods

Results

Conclusion