A stable isotopic study of the diet of <i>Potamonautes sidneyi</i> (Brachyura: Potamonautidae) in two coastal lakes of the iSimangaliso Wetland Park, South Africa

Abstract

Potamonautes sidneyi Rathbun 1904, is a dominant freshwater crab in KwaZulu-Natal, South Africa. Recent flood events in the iSimangaliso Wetland Park have allowed a substantial range expansion of this species, including previously hypersaline and desiccated areas. A stable isotope study was conducted to examine the feeding habits of the populations from Lake Sibaya and Mpophomeni Stream, two contrasting sites in the iSimangaliso Wetland Park. Juveniles from Mpophomeni Stream were more depleted in δ 13 C and more enriched in δ 15 N compared to adults, indicating a more carnivorous diet and higher trophic position. A general shift in diet was observed at both sites, with consumption of aquatic invertebrates and sedimentary organic matter more prevalent in the wet summer months, while greater proportions of detritus and microphytobenthos were consumed in autumn/winter. No significant difference was observed between adults from the two sites despite the abiotic variations. The species appears to play a complex role in the trophic web, by acting as an intermediate consumer facilitating the flow of nutrients across levels and by breaking down decomposing organic matter, allowing for rapid recycling of nutrients within its ecosystem.

In a Pinch: Mechanisms Behind Potential Biotic Resistance Toward Two Invasive Crayfish by Native African Freshwater Crabs

“…This is potentially due to evolutionary competition with freshwater crabs (Ortmann, 1902;Lodge et al, 2012;Nunes et al, 2017a). Freshwater crabs of the genus Potamonautes are, however, present in almost all African freshwater habitats where they are trophically analogous to freshwater crayfish and provide essential nutrient cycling services (Hill and O'Keeffe, 1992;Dobson, 2004;Cumberlidge and Daniels, 2009;Peer et al, 2015). Potamonautid species typically exhibit high degrees of endemism and range restriction.…”

Let's get high: Cladogenesis in freshwater crabs (Decapoda: Potamonautidae: Potamonautes) supports the mountain gradient speciation hypothesis in the Cape Fold and Drakensberg Mountains, South Africa

“…Consequently, the feeding guilds among the mountain freshwater crab species are unknown; however, freshwater crabs are known to be dietary generalist and detrital feeders (Peer et al, 2015).…”

Trophic niche of an invasive generalist consumer: Australian redclaw crayfish,Cherax quadricarinatus, in the Inkomati River Basin, South Africa

“…Sidney's river crabs are omnivores, where adults are mainly herbivores and detritivores, whereas juveniles appear to favour a carnivorous diet (Peer et al . 2015). This omnivorous feeding behaviour is well supported by results from this study, where Sidney's river crabs were polytrophic and had a large niche size, inferring a broad‐based diet.…”