Nutrient dynamics and successional changes in a lentic freshwater biofilm

Abstract

SUMMARY 1. Colonisation, species composition, succession of microalgae and nutrient dynamics in biofilms grown under light and dark conditions were examined during the initial phases of biofilm development in a lentic freshwater environment. 2. Biofilms were developed on inert (perspex) panels under natural illuminated and experimental dark conditions and the panels were retrieved for analysis after different incubation periods. Analysed parameters included biofilm thickness, algal density, biomass, chlorophyll a, species composition, total bacterial density and nutrients such as nitrite, nitrate, phosphate and silicate. 3. Biofilm thickness, algal density, biomass, chlorophyll a and species richness were significantly higher in light‐grown biofilms, compared with dark‐grown biofilms. The light‐grown biofilms showed a three‐phased succession pattern, with an initial domination of Chlorophyceae followed by diatoms (Bacillariophyceae) and finally by cyanobacteria. Dark‐grown biofilms were mostly dominated by diatoms. 4. Nutrients were invariably more concentrated in biofilms than in ambient water. Nutrient concentrations were generally higher in dark‐grown biofilms except in the case of phosphate, which was more concentrated in light‐grown biofilms. Significant correlations between nutrients and biofilm parameters were observed only in light‐grown biofilms. 5. The N : P ratio in the biofilm matrix decreased sharply in the initial 4 days of biofilm growth; ensuing N‐limitation status seemed to influence biofilm community structure. The N : P ratios showed significant positive correlations with the chlorophycean fraction in both light and dark‐grown biofilms, and low N : P ratio in the older biofilms favoured cyanobacteria. Our data indicate that nutrient chemistry of biofilm matrix shapes community structure in microalgal biofilms.

Diversity and biomass accumulation in cultured phototrophic biofilms

“…In most instances, species that colonized rapidly tended to be replaced by slower colonizing species (mainly cyanobacteria). Similar community changes, in combination with diversity reduction in ageing biofilms and cyanobacterial dominance, were also found in natural freshwater biofilms (Sekar et al, 2002). The decrease in diversity probably indicated a greater contribution to the community of the growth of species already present on the substrata compared with the settlement of new species, especially under nutrient replete conditions and reduced availability of bare substrata (Hillebrand & Sommer, 2000).…”

“…Diversity of the community was also shown to decrease from the initial to mature phases of biofilm development, reflecting the constant microcosm environmental conditions (Sekar et al, 2002;Paule et al, 2011), which may have enhanced competitive exclusion. In most instances, species that colonized rapidly tended to be replaced by slower colonizing species (mainly cyanobacteria).…”

“…This probably reflects a combination of colonization ability and light resource competition but it is difficult to separate their effect on community composition. Bacteria and fast-growing microalgae are known pioneer species responsible for colonization of substrata (Sekar et al, 2002). The fast-growing green algae, Chlorococcum, Desmodesmus and Scenedesmus, are probably responsible for the shorter lag phase in biofilms grown at higher irradiances.…”

Efeito de diferentes níveis de enriquecimento por fósforo sobre a estrutura da comunidade perifítica em represa oligotrófica tropical (São Paulo, Brasil)

“…Diferentemente, a razão N:P da água indicou condição P-limitante em todos os tratamentos, apesar da alteração estequiométrica entre nitrogênio e fósforo. Tais resultados estão de acordo com Sekar et al (2002), que reportaram maior concentração de nutrientes no biofi lme perifítico do que na água, encontrando razão N:P do perifíton sempre menor do que a água devido à bioacumulação de fósforo.…”

Divergent composition of algal-bacterial biofilms developing under various external factors

“…Changes in biofilm composition with age will bring about changes in the way the biofilm modifies the quality of the overlying water and uses nutrients, ultimately changing the transfer of substances between the benthos and the water column (Sekar et al, 2002;Van der Grinten et al, 2004).…”