Estuaries and Coasts

, Volume 41, Issue 5, pp 1463–1474 | Cite as

Appraisal of Warm-Temperate South African Mangrove Estuaries as Habitats to Enhance Larval Nutritional Condition and Growth of Gilchristella aestuaria (Family Clupeidae) Using RNA:DNA Ratios

  • Eugin Bornman
  • Nadine Strydom
  • Catriona Clemmesen


Estuaries are highly dynamic systems that serve as nursery areas to fishes and are likely to vary in nursery function, mostly due to habitat quality and food availability. Mangroves are thought to be good nurseries as they enhance food availability and protection, improving growth and survival of juvenile fishes. Food quantity and quality may be reflected in nutritional condition, which may in turn be a useful proxy for growth and survival of larval fishes. This study compared the nutritional condition and growth rate of 793 late stage larvae of estuarine roundherring, Gilchristella aestuaria, by using RNA:DNA indices to indirectly compare the feeding environment among similar warm-temperate mangrove and non-mangrove estuaries in South Africa during January 2015 and 2016. Results indicated that G. aestuaria larvae had differing nutritional conditions within the sampling years and within the estuaries. The standardised RNA:DNA (sRD) as well as the RNA residual index values were higher within mangrove estuaries only in 2016. The instantaneous growth rates (Gi) of larvae in mangrove and non-mangrove estuaries were similar; however, post-flexion larvae were found to have a higher Gi and sRD in mangrove estuaries. Turbidity was the major factor influencing the nutritional condition of G. aestuaria larvae. Mangroves have been found to act as sediment sinks and thus may provide advantages that increase feeding success for post-flexion larvae; however, more is yet to be understood in terms of feeding environment dynamics and how habitat quality influences the survival of larval fishes.


Nursery habitats Mangroves Fish feeding environments RNA:DNA Nutritional condition Estuarine roundherring Fish larvae 



We thank Helmholtz Centre for Ocean Research (GEOMAR) for laboratory assistance supported by the EU project BIOC3. We also thank the South African Weather Service for providing rainfall data.


Funding was provided by the National Research Foundation of South Africa under grant number 93570.

Compliance with Ethical Standards

Conflict of Interest

The co-author, Nadine A. Strydom, is the M.Sc. supervisor of the first author and is an associate editor of Estuaries and Coasts. The authors declare that there are no other conflicts of interest.

Ethical Approval

Fishes were treated in accordance with Nelson Mandela University ethics, under ethics clearance number A15-SCI-ZOO-002.


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Copyright information

© Coastal and Estuarine Research Federation 2018

Authors and Affiliations

  • Eugin Bornman
    • 1
  • Nadine Strydom
    • 1
  • Catriona Clemmesen
    • 2
  1. 1.Department of ZoologyNelson Mandela UniversityPort ElizabethSouth Africa
  2. 2.Helmholtz Centre for Ocean Research (GEOMAR)KielGermany

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