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RESEARCH ARTICLE
Contents Vol 59(7)

Effects of sewage discharges on microbial components in tropical coastal waters (Senegal, West Africa)

Marc Bouvy A E , Enora Briand B , Maimouna M. Boup C , Patrice Got A , Christophe Leboulanger A , Yvan Bettarel C and Robert Arfi D
+ Author Affiliations
- Author Affiliations

A IRD UR 167, UMR ECOLAG, Université Montpellier II, Case 093, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France.

B USM505, Écosystèmes et interactions toxiques, Muséum National d’Histoire Naturelle, 57 rue Cuvier, case 39, 75231 Paris Cedex 05, France.

C IRD UR 167, Centre IRD-ISRA, BP 1386 Dakar, Senegal.

D IRD UR 167, Centre d’Océanographie de Marseille, 13007 Marseille, France.

E Corresponding author. Email: bouvy@mpl.ird.fr

Marine and Freshwater Research 59(7) 614-626 https://doi.org/10.1071/MF07244
Submitted: 18 December 2007  Accepted: 13 May 2008   Published: 24 July 2008

Abstract

Coastal ecosystems are frequently submitted to anthropogenic pressure but little is known about how the dynamics of aquatic communities can be altered. The impact of urban and industrial discharges on microbial plankton was studied in Hann Bay near Dakar (Senegal) on the Atlantic Ocean. Spatial patterns were studied using three transects, with a total of 20 stations, during two periods in May and November (before and after the seasonal upwelling), revealing a clear contrast between near shore stations and the intermediate and seaward stations. In November, phytoplankton were associated with dissolved nutrient availability (e.g. with nitrate, r = 0.76) whereas in May, phytoplankton were more correlated with microbial variables (e.g. with heterotrophic nanoflagellates, r = 0.63). Most samples (40) failed to meet the quality levels for the faecal indicator bacteria (FIB) defined by the European Union bathing water quality directive. The topography plays a major role in water circulation explaining the presence of FIB at the seaward stations. The high prevalence of FIB during the two periods suggests chronic pollution and a potential risk to recreational swimmers and fish consumers in Hann Bay. Thus, as demonstrated in various temperate systems, the decline of water quality constitutes a serious problem in many West African countries.

Additional keywords: coastal bay, faecal indicator bacteria, microbial loop, nutrient.


Acknowledgements

This work is a contribution to the program of IRD Research Unit 167. We thank François Sanséo for the sea sampling, and Daniel Corbin for chemical analysis. The present study is part of the Aurélie Lemeur’s research supervised by M.B. We are grateful to the Editor and two reviewers for their criticisms and constructive comments.


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