Factors driving diversity and succession of diatom assemblages in a Neotropical rainforest stream

This study assessed short-term succession and related changes in diversity and succession of benthic diatom assemblages in a tropical rainforest stream in the biogeographic region of Choco, Colombia. Diatom colonization in situ was studied over a 60-day period, in which we analyzed the number of valves and the taxonomic changes. The Shannon index ranged from 2.06 to 3.02 bits. A total of 127 species were identified and the most abundant were acidophilic species such as Eunotia intermedia, E. veneris, E. bilunaris var mucophila, E. pirla and E. bilunaris. A Detrended Canonical Correspondence Analysis (DCCA) was used to explore the succession of diatom assemblages and its driving environmental factors. The DCCA explained 74.1% of the correlation between environmental variables and diatom species and 16.2% of the data variance. The species fell into four groups, the first group (Eunotia incisa, Frustulia saxonica, Fragilaria capucina var acatu, among others) was related to lower nitrate concentrations, acidic pH and lower water temperature. The second group (Fragilaria capensis, Gomphonema olivaceum, Cymbella gracilis, among others) was associated to higher alkalinity and lower solar radiation availability. The third group (Nitzschia obtusa, N. amphibia, Naviculadicta vitabunda, Navicula cryptocephala, among others) was related to lower phosphate, higher nitrate concentrations, lower pH, and higher temperatures. The fourth group (Eunotia soleirolli, Frustulia vulgaris and F. rhomboides) was associated with higher solar radiation and lower alkalinity. These results underscore the importance of diatom diversity in Neotropical streams and the relevance of small variations in environmental factors on the composition of reference assemblages of Neotropical fluvial systems.