%0 Journal Article
%T Distribution and dynamics of a tropical waterfalls ecosystem Distribution et dynamique d'un ¨¦cosyst¨¨me tropical de cascades
%A Offem B.O.
%A Ikpi G.U.
%J Knowledge and Management of Aquatic Ecosystems
%D 2012
%I EDP Sciences
%R 10.1051/kmae/2012004
%X Waterfalls gives the impression of a lifeless zone because researchers have historically focused on the hydrology, ecotourism and geological features. Effective management will require an understanding of changes in species composition and distribution of macro-biota. Monthly samples were taken in wet and dry seasons, over two year period in three regions along the 6817.7 m length of the Agbokum waterfalls. Macro-biota exhibited distinct pattern in respect of seasonal and spatial changes. Trachelomonas volzii, the most abundant phytoplankton species reduced from 686 in the dry season to 143 in the wet, and from 455 downstream to 91, midstream (waterfalls region). Zooplankton species Calanus finmarchicus decreased from 511 during dry season to 36 in the wet and from 334 downstream to 7, midstream. 71.7 percent of the total macro-invertebrates were recorded from downstream reaches while only 6.3 percent were contributed by midstream. Percentage cover of marginal vegetation by Bambusasp, Symphonia and Elaeis guineesis displayed progressive increase from upstream reaching a maximum of 38.5 mean percent cover in the relatively undisturbed downstream. In contrast, Raphia vinifera, Havea brasiliensis, Grewia sp. and Cocos nucifera shrank in size from 34% to 8% at the midstream stretches of the river while only nymphia- rich vegetation becomes more frequent in the middle reaches. The disturbance regimes of the midstream reaches of Agbokum waterfalls combined with its very low faunal and floral diversity has made the environment unstable therefore susceptible to the invasion of disturbance tolerant biota. Les cascades donnent l'impression d'une zone morte parce que les chercheurs ont toujours mis l'accent sur l'hydrologie, l'¨¦cotourisme et les caract¨¦ristiques g¨¦ologiques. Une gestion efficace n¨¦cessite la compr¨¦hension des changements dans la composition des esp¨¨ces et la distribution des macro-organismes. Des ¨¦chantillons mensuels ont ¨¦t¨¦ pris au cours des saisons humides et s¨¨ches, pendant plus de deux ans dans trois r¨¦gions le long des 6817,7 m des cascades Agbokum. Les macrobiotes pr¨¦sentent des patterns diff¨¦rents selon les changements saisonniers et spatiaux. Trachelomonas volzii, l'esp¨¨ce de phytoplancton la plus abondante, passe de 686 en saison s¨¨che ¨¤ 143 en saison humide, et de 455 en aval ¨¤ 91 en zone m¨¦diane (r¨¦gion des cascades). L'esp¨¨ce de zooplancton Calanus finmarchicus passe de 511 pendant la saison s¨¨che ¨¤ 36 en saison humide et de 334 en aval ¨¤ 7, en zone m¨¦diane. 71,7 % du total des macro-invert¨¦br¨¦s ont ¨¦t¨¦ rencontr¨¦s dans les tron ons sit
%K waterfalls
%K macro-invertebrates
%K phytoplankton
%K zooplankton
%K vegetation
%K fish species
%K physic-chemical properties
%K cascades
%K macro-invert¨¦br¨¦s
%K phytoplancton
%K zooplancton
%K v¨¦g¨¦tation
%K esp¨¨ces piscicoles
%K propri¨¦t¨¦s physico-chimiques
%U dx.doi.org/10.1051/kmae/2012004