Using stable δ13C and δ15N isotopes to assess foodweb structures in an African subtropical temporary pool

Abstract

Southern Africa has one of the highest densities of temporary pools and some of the most understudied temporary wetlands in the world.  Additionally, the eastern African annual killifishes (Nothobranchius spp.) are rare in southern Africa and found exclusively in temporary habitats.  There is a notable lack of literature regarding the diet of these fish, as well as the foodweb structures of temporary ecosystems. The current study aimed to address this paucity in literature by assessing the foodweb of a temporary pool located in the Ndumo Game Reserve (NGR) in northern Kwa-Zulu Natal using stable isotopes analysis. In addition, Bayesian mixing models were used to assess the diet of the spotted killifish Nothobranchius orthonotus over two seasons (dry and wet seasons). The foodweb consisted of only three trophic levels and comprised different foodweb items between the two seasons. Stable isotope analysis indicated significant increases in δ15N from the dry to wet season. It further revealed the diet of N. orthonotus to be more varied and omnivorous with primary producers contributing a much greater percentage toward their  diet than previous studies have reported. This study contributes valuable information to the paucity of knowledge regarding foodweb structure and food-chain length of temporary pools in South Africa, as well as new insights into the extended diet of N. orthonotus. The analytical techniques used  in this study could also be utilised as part of future research in ecological assessments of temporary pools and other aquatic ecosystems in Africa and globally.

Keywords: Bayesian analysis, killifish, mixing models, MixSIAR, Nothobranchius orthonotus, Phongolo floodplain, southern Africa