Could the inter-specific competition be the determinating factor of the internal dynamics of a cyanobacterial bloom?

FERNÁNDEZ, C; PARODI, E. R

Rio de Janeiro, Brasil

Conferencia; 7th International Conference on Toxic Cyanobacteria; 2007

In Argentina, the Paso de las Piedras reservoir (38º22´S and 61º12´W) supplies potable water to 500,000 inhabitants of the cities of Bahía Blanca and Punta Alta and outskirts. Massive proliferations of Cyanobacteria happen in it repeatedly, causing different problems, from the generation of scents and disagreeable flavours to the clogging of the filters of the water-treatment plant, and exceptionally the production of cyanotoxins. There are consensus that the key factors commanding blooms are high concentrations of N and P, high temperatures and pH, absence of turbulence. Nevertheless the present study of the temporary dynamics of a cyanobacterial bloom ­- made between January and April of 2004 - suggests that the cyanobacterial inter-specific competition played a significant role in the dynamics of the populations, since physical and chemical parameters did not presented dramatic variations during the bloom. Sub-surface samples of phytoplankton were collected for qualitative and quantitative analysis and physical and chemical parameters were registered. The most abundant species were: Woronichinia sp., Microcystis natans, M. aeruginosa, M. flos-aquae, Anabaena circinalis and Snowella lacustris; being the four last potential producers of toxins. Microcystis was the genus better represented and M. natans and M. flos-aquae were the most abundant species, during January-April and March-April respectively. M. aeruginosa was observed on the surface of the lake throughout the entire bloom. Anabaena circinalis presented the greater abundance during February-March, whereas Woronichinia sp. was observed from March to May. Snowella lacustris appeared only in April. (PGI UNS 24/B119).