Seasonal variations and distribution of diatom flora of Lake Ahémé (Benin, West Africa)

ABSTRACT

Lake Ahémé (part of Ramsar 1017) is one of the most productive brackish water ecosystems and is the second-largest lake in Benin in terms of area, after Lake Nokoué. However, this lake has received little attention for hydrobiological studies, although it is subject to heavy pollution. Therefore, the present study aims to contribute to the monitoring of Lake Ahémé, by assessing the diatom flora. For this purpose, eight sites were surveyed during the dry and wet seasons between September 2014 and 2016. Physico-chemical parameters were measured and diatoms were collected using a phytoplankton net. Margalef, Simpson, Shannon-Weaver, Pielou Equitability and Berger-Parker diversity indices showed significant diversity in Lake Ahémé. The n-MDS and ANOSIM analyses of the diatom communities showed heterogeneity according to seasons and sites. SIMPER analysis revealed that Aulacoseira granulata, Entomoneis paludosa, Nitzschia sigma, Nitzschia linearis, Tryblionella debilis, Thalassiosira lacustris, Cyclotella sp., Iconella capronii, Iconella robusta and Cerataulina bicornis contributed to the changes in diatom community structure. Redundancy analysis showed that temperature, pH, conductivity, total dissolved solids and dissolved oxygen were driving factors in the distribution of diatoms species in Lake Ahémé. The influence of the Atlantic Ocean on Lake Ahémé is noted through the presence of high salinity tolerant species such as Entomoneis paludosa, Nitzschia closterium, Nitzschia sigma and Coscinodiscus wailesii. Further taxonomic research is needed to better understand diatom ecology and species biogeographical distribution.

KEYWORDS:

• Benin
• biogeography diatoms
• diversity
• heterogeneity
• Lake Ahémé

Acknowledgments

The authors are grateful to the Belgian National Focal Point for the Global Taxonomy Initiative (CEBioS programme of the Royal Belgian Institute of Natural Sciences), the financial support of the Belgian Development Cooperation, which granted Isabella Olodo a travel internship grant for taxonomic capacity building during which this manuscript was improved. Also, our thanks go to the Organization of Women in Science for Development (OWSD) for their financial support. The “Association des Diatomistes de Langue Française” (ADLaF) in partnership with the Meise Botanic Garden were of crucial importance for the writing of this article.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Isabella Yasmine Olodo

Isabella Yasmine Olodo is a PhD student in tropical water ecology at the University of Abomey-Calavi, Benin. She is currently studying phytoplankton diversity and distributions in Lake Ahémé, Benin. Contribution: She is the lead investigator, collected samples, analysed, and prepared the first draft of the manuscript.

Christine Cocquyt

Christine Cocquyt is a senior researcher at the Meise Botanic Garden (Belgium) and has been studying phytoplankton and diatoms in tropical Africa for nearly four decades. She is involved in the taxonomy of diatoms, particularly in East Africa, DR Congo and the Sahara region of Chad. Contribution: She helped in diatom analysis and in writing parts of the first manuscript draft.

Youssouf Abou

Youssouf Abou is a full professor in hydrobiology and ecology of continental waters at the University of Abomey-Calavi. He is involved in numerous research projects on phytoplankton in Benin’s lakes, lagoons and reservoirs. Contribution: sample collection and analysis and research conceptualization.

Kouami Kokou

Kouami Kokou is a full professor in botany at the Natural Resource Management and Forest Ecology, University of Lomé. He works on microalgae in West Africa, particularly in rivers and lakes of Togo. Contribution: sample processing and analysis and writing of the first draft.