The concept of ecological succession applied to phytoplankton over four consecutive years in five ponds featuring a salinity gradient |
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Authors: | Hajer Khemakhem Jannet Elloumi Mahmoud Moussa Lotfi Aleya Habib Ayadi |
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Affiliation: | 1. Université de Sfax, Faculté des Sciences de Sfax, Département des Sciences de la Vie. Unité de recherche UR/05ES05 Biodiversité et Ecosystème Aquatiques, Route soukra Km 3,5, B.P. 1171, CP 3000 Sfax, Tunisia;2. Laboratoire d''Hydraulique, Ecole Nationale d''Ingénieurs de Tunis, BP 37, Le Belvédère, 1002 Tunis, Tunisia;3. Université de Franche-Comté, Laboratoire de Chrono-Environnement, UMR CNRS 6249, 1, Place Leclerc, F-25030 Besançon cedex, France |
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Abstract: | The distribution of phytoplankton abundance, biomass and species composition coupled with environmental factors and metazooplankton was studied relatively intensively and over a period of four consecutive years in five ponds featuring a gradient of increasing salinity from near to that of sea water to a nine-fold concentration from 2000 to 2003. The results indicate that the physical characteristics of the water (temperature and salinity) were quite similar over the years. Nutrients, which were concentrated in pond A1, decreased with increases in salt concentration. The composition of the phytoplankton community showed strong seasonality. Diatoms dominated in the first ponds A1, A16 and C2-1, followed by dinoflagellates. Chlorophyceae dominated the phytoplankton community in the hypersaline ponds M2 and TS. Cyanobacteriae were relatively abundant in ponds M2 and TS. The highest phytoplankton density and biomass were found in the ponds with the highest salinity due to the proliferation of Dunaliella salina (Chlorophyta: Volvocales). The inter-annual study of phytoplankton succession in the Sfax solar salterns showed slight differences among the years of study due to the stability of the environmental conditions. Phytoplankton communities were permanently primitive, stage 1 – structured as they failed to build complexity because of salt stress which operates for longer and above any other variables. This reduced frequency of disturbance to the existing course of regulation, allowed the community to “mature” from its “primitive” state, rather than experience frequent structural setbacks. |
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Keywords: | solar salterns phytoplankton zooplankton diversity disturbance concept |
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