This study aimed at evaluating the time scale influence (successional and seasonal) on the periphyton biomass, diversity, and algal community structure in a tropical oligotrophic reservoir, southeast Brazil. Succession process was followed during dry and rainy periods by every 3-day samplings over 27 days, and included 16 abiotic variables and periphyton properties on artificial substrate. Chlorophyll-a values were low and similar between periods, however, with the highest loss rates observed during the rainy season. Shannon diversity was high (3.4-4.5 bits ind-1) and relatively stable among periods and along the entire succession. Chlorophyceae was the most abundant class over succession, mainly represented by Chlamydomonas planctogloea Skuja that contributed with 23% (dry) and 37% (rainy) of the mean total density. Integrated analysis of species and environmental variables revealed climatic period as the main driving force on periphyton structure. Oocystis lacustris Chodat and Gymnodinium sp. were associated with dry period and lower temperature and ammonium values, as well as with higher pH, dissolved oxygen, and total phosphorus levels. Frustulia rhomboides (Ehr.) de Toni var. rhomboides and Cosmarium majae Strom were associated with rainy season and, inversely, to the dry season abiotic variables. Periphyton community was mainly controlled by the climatic period, the autogenic succession being of less importance. Photosynthetic biomass accrual process and periphytic algal species assemblages were more sensitive to such variation. Present results contribute to a better understanding of the periphyton community structuring in oligotrophic reservoirs, providing a reference for changes in degraded tropical systems.
biomass; community structure; diversity; periphyton; richness
