Environmental factors controlling the dynamics of filamentous bloom-forming cyanobacteria in a hypereutrophic shallow lake (Buenos Aires province, Argentina)

R. ECHENIQUE; A. AGUILERA; L. AUBRIOT; G.L. SALERNO

Florianópolis

Congreso; The 17th International Conference on Harmful Algae; 2016

International Society for the Study of Harmful Algae (ISSHA)

The seasonal dynamics of phytoplankton was studiedfrom July 2012 to May 2014 in a temperate, hypereutrophicshallow lake. The aimof the study was to determine the environmental factors that control thedominance and succession of blooms-forming filamentous cyanobacteria which donot form aggregations. In situ environmental measurements, nutrient andphytoplankton samples were taken fortnightly.Field work was complemented with laboratory assays where the coexistence of twofilamentous cyanobacteria isolated from the shallow lake (Planktothrixagardhii and Raphidiopsis mediterranea) was tested under two lightintensities (40 and 80 µmol photon m-2 s-1) and twophosphate concentrations (5 and 200 µM K2HPO4). P.agardhii (functional group S1) wasthe dominant species during the whole sampled period, followed by the Nostocales R.mediterranea (SN), Aphanizomenon gracile andSphaerospermopsis aphanizomenoides (H1)which biomass was positively influenced by temperature and light availability(summer seasons). Contrary to predictions, nitrogen deficient conditions (NT:NPratios ~ 5) did not lead to the dominance of Nostocales. On the contrary, themassive growth of P. agardhii inducedextremely low light conditions thatled to the collapse of this group in early autumn. This collapse is thought tohave represented an important pool of N and P that was used by P. agardhii. In co-culture experiments,the growth of R. mediterranea wasstrongly promoted under 80 µmol photon m-2 s-1 and both phosphateconcentrations, whereas P. agardhii didnot tolerate high light conditions. Together, these findings high-lights theimportance of light availability and self-shading in structuring the phytoplanktondominated by filamentous cyanobacteria.