Diet and isotopic metrics of predatory and prey fish in two estuaries with different degrees of anthropogenic disturbances: the case study of Wami and Pangani rivers in Tanzania


Submitted: 18 July 2021
Accepted: 24 November 2021
Published: 21 December 2021
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Authors

  • Theresia John Lyasenga School of Aquatic Sciences and Fisheries Technology, University of Dar es Salaam, Tanzania, United Republic of.
  • Alistidia Paul Mwijage Tanzania Fisheries Research Institute (TAFIRI), Dar es Salaam, Tanzania, United Republic of.
  • Dativa Joseph Shilla Department of Chemistry, Dar es Salaam University of College of Education (DUCE), Tanzania, United Republic of.
  • John Andrew Marco Mahugija College of Natural and Applied Sciences, Department of Chemistry, University of Dar es Salaam, Tanzania, United Republic of.
  • Lydia Gaspare School of Aquatic Sciences and Fisheries Technology, University of Dar es Salaam, Tanzania, United Republic of.
  • Daniel Abel Shilla School of Aquatic Sciences and Fisheries Technology, University of Dar es Salaam, Tanzania, United Republic of.
  • Prosper Laurent Mfilinge School of Aquatic Sciences and Fisheries Technology, University of Dar es Salaam, Tanzania, United Republic of.

Diverse anthropogenic activities including alteration of hydrological regime and agricultural development in the upstream of the river catchments modify the structural components and ecological roles of the species in estuarine ecosystems. The present study compared the diet, carbon (δ13C) and nitrogen (δ15N) isotopic signals, trophic niches and metrics of trophic redundancy of predatory fish and their potential phytodetritivore prey-fish between two estuaries with different degrees of anthropogenic disturbances. The δ13C and δ15N signals, Bayesian mixing models and stomach content analyses were adopted. It was revealed that the diet among the predators Arius africanus, Epinephelus coioides, Sillago sihama and Pomadasys argenteus and their isotopic signals including their phytodetritivore-prey, Valamugil buchanani were significantly different between Wami and Pangani estuaries (PERMANOVA, Pseudo –F ≥ 3.1, p = 0.05). The total isotopic niche area between estuaries accounted by the comparable Bayesian standard ellipse area (SEAb) was significantly smaller in Wami than that of Pangani (t-test, t = 4.3, p < .001). The ANOVA test further confirmed significant variation in SEAb among fish populations in two estuaries (F = 27.84, p < 0.001). The Layman metric indices of trophic diversity and redundancy of Wami estuary were substantially smaller than those observed at Pangani estuary. These findings mean that despite Wami estuary being under conservation status, the extent of disturbances in the upstream is high enough to induce the ecological changes at the base of the food web, subsequently cascading its effect up to the higher-order consumers of the ecosystem. As a result, the ecological redundancy and ecosystem complexity of Wami is somewhat compromised relative to that of Pangani estuary. Therefore, the degree of anthropogenic disturbances in river catchments affect differently the trophic niches of predatory and phytodetritivore fish and hence overall food web structures, trophic redundancy and complexity of estuarine ecosystems.


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Alistidia Paul Mwijage, Tanzania Fisheries Research Institute (TAFIRI), Dar es Salaam

Alistidia Paul Mwijage has a Ph.D. in aquatic sciences obtained from the University of Dar es Salaam in 2019. He received a bachelor's degree in Environmental Science and management from Sokoine University of Agriculture (SUA), and a master's degree in Integrated Environmental Management (physical sciences) from the University of Dar es Salaam, Tanzania. She is currently employed by a government institution as a researcher at the headquarters of the Tanzania Fisheries Research Institute (TAFIRI). Her research area of interest includes: - estuarine and coastal ecology particularly food web indices describing the ecosystem functioning and stability, habitats and trophic connectivity.

Ethics Approval

estuarine trophic dynamics of fish and ecosystem functioning

Supporting Agencies

University of Dar es Salaam

John Lyasenga, T., Mwijage, A. P., Shilla, D. J., Marco Mahugija, J. A., Gaspare, L., Shilla, D. A., & Laurent Mfilinge, P. (2021). Diet and isotopic metrics of predatory and prey fish in two estuaries with different degrees of anthropogenic disturbances: the case study of Wami and Pangani rivers in Tanzania. Advances in Oceanography and Limnology, 12(2). https://doi.org/10.4081/aiol.2021.9987

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