Phytoplankton community structure and species assemblage succession in a shallow tropical lake (Lake Guiers, Senegal)

Abstract

Phytoplankton species composition and seasonal changes were investigated monthly in Lake Guiers, one of the largest lakes in West Africa. Taxonomic composition, diversity, biovolume and abundance of phytoplankton were studied at 3 representative stations from March 2002 to March 2003, in relation to various climatic factors (wind, insolation), physical and chemical factors (temperature, conductivity, nutrients) and biological factors (zooplankton grazing). A total of 111 species of phytoplankton belonging to 7 algal classes were identified, predominately Chlorophyceae (32% of species) followed by Cyanobacteria (25%) and Bacillariophyceae (diatoms, 15%). From December to March, a period characterised by low temperature, solar insolation and north-easterly winds that mixed the water column, the community was dominated by the diatom Fragilaria sp. and cyanobacterium Anabeana miniata. From April to September, during higher temperatures, solar insolation and predominant north-westerly winds that mixed the water column less effectively, the community was dominated by cyanobacteria Cylindrospermopsis raciborskii and Lyngbya versicolor. A statistical approach based on co-inertia analysis was used to describe the phytoplankton/ environment relationships, in particular the factors governing the presence of C. raciborskii. The phytoplankton community was characterised by a clear succession of species groups: Fragilaria sp.-A. miniata (November to March) → → Microcystis aeruginosa (March to May) → → C. raciborskii-L. versicolor (June to November). Finally, a functional approach originally designed for temperate zones was applied to the algal groups (11 functional groups), which gave valuable information on algal strategies in a shallow tropical lake. KEY WORDS: Phytoplankton · Cylindrospermopsis · Fragilaria · Functional group · West Africa Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 45: [147][148][149][150][151][152][153][154][155][156][157][158][159][160][161] 2006 pressure exerted by one or many predators, acting simultaneously within a community in a particular habitat or space. Cyanobacteria are more abundant than other classes of algae in most shallow tropical lakes, and are often competitors under conditions of high turbidity (Padisák 1997).Algal successions in tropical aquatic systems are generally characterised by a sharp contrast between the 2 main seasons (dry/wet-flood season): cyanobacteria/diatoms in Lake Victoria (Lung'ayia et al. 2000), cyanobacteria/chlorophytes-chroococcales in Lake Tanganyika (Descy et al. 2005) and cyanobacteria/ diatoms-chlorophytes-chroococcales in many reservoirs in north-east Brazil (Bouvy et al. 2000. According to Salmaso (2003), temporal changes in phytoplankton composition can represent a complex environmental gradient driving annual succession; thus, environmental variables may act jointly as a complex forcing factor that selects seasonal groups of species sharing similar requirements. In a given environment and for...

Role of atelomixis in replacement of phytoplankton assemblages in Dom Helvécio Lake, South-East Brazil

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Phytoplankton abundance, dominance and coexistence in an eutrophic reservoir in the state of Pernambuco, Northeast Brazil

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