CYANOPHlYTA FROM FOUR SMALL PONDS OF THE PLATENSE AREA I SEASON AL VARUATION AND WATERBLOOMS.

Abstract

The aim of this papel' is to descrihe Cyanophyta waterblooms as well as their seasonal variation at surface and their qualitative-quantitativecomposition in four small ponds of the Platense Area. Itis also here demonstrated tbat intensity, duration and periodicity of waterbloomsvary uccordin,g to the species producing tbis pbenomenon, to the different seasonsand to eco!ogical conditions of tbe habitat. Tbe waterbodies consideredin this investigation are placed in Los Talas locality, district of Berisso. Eachof these small ponds has an area of circa 1 ha and a range of depth between0.50 - 2.40 m. Samples were collected montbly during January 1981 - ApriJ 1983.Two sampling stations were selected in eacb pond: a coastal station (at 30-50 cmfrom the coast) and a central station (at 30-50 m from the coast). Quantitativeana!ysis was done by means of Sedgwick-Rafter method with Jess than 20 %error. Tbirty-one species of Cyanophyta included into sixteen genera were identified.Among tbese, OscilLatoria (with 5 species), Microcystis (with 4 species),Anabaena (witb 3 species) and Merismopedia (with 3 species) are the bestrepresented genera. Oscilla/ori<l agardhii, O. allglls/a and Raphidiopsis mediterTllneaare the more abundant species. n1e greater specific richness is observedin surnmer, being constant 01' increasing to autllmn and decreasing considerablyduring winter. No important differences between species at the coasta! stationand those of the central were observed. Moreover, Cyanophyta abso!ute abundancein the two sampling statíons of the four ponds studied is similar. Waterhloomsof Anabaefl(l spiroides, A. sphaerica var. mierosperma, Anaboellopsis arno/dij,Oscil/atoria ongllsta, O. agardhii, Pselldanobaena eotenata, Rapllidio/lsisCltTI;ata, R. mediterranea and Spirlllina laxissima were observed. Those callsedby O. agardhii and S. laxissima are !onger than those ori.ginateel by A. spiroides,A. artlOldi'Í, P. eatenata, H. el/mata unel R. mediterranea. P. eatenata anel A.spiroides waterblooms are monospecific while those of A. amo/dii, R. cllrvataanel H. mediterranea coexist with other subdominant species.