Seasonal persistence and stability of diatom communities in rivers: are there habitat specific differences?

Epilithic, epiphytic and epipelic diatoms were sampled at four sampling stations monthly from June to October in three boreal rivers in South Finland to examine the seasonal community persistence and stability of diatom communities in three habitats. The variation of successive samples in ordination space using Non-Metric Multidimensional Scaling was substantial and without an evident pattern; there were no clear differences between community stability on three different substrata. At two stations, Multi Response Permutation Procedures showed significant among-group differences indicating that diatom communities were distinctly different among the three substrata. According to Indicator Species Analysis, we found several species showing significant (p < 0.05) specificity for, and fidelity to, certain substrata at two stations. The stability between sampling months in the rank abundance of diatom taxa was lowest among epiphytic communities. At each station, Spearman rank correlation decreased substantially until August indicating a distinct change in rank abundances. Communities tended to revert to their pre-disturbance state toward autumn after a major spate in the end of August. Using linear regression, we found that changes in total P were significantly (p < 0.05) related to community stability in the epilithon. Species turnover seemed to be highest among epiphyton and lowest among epipelic communities. Although these differences could partly result from lower diversity in epiphyton, they probably reflect lower persistence among epiphytic communities in these boreal rivers.