Ecology of the major periphytic diatom communities from the Mesta River, Bulgaria

Epilithon, epiphyton, epipelon, epipsammon and plocon diatom samples and wa ter chemistry samples were collected bimonthly from 11 stations along the M esta River, Bulgaria between December 1989 and April 1991. Principal compon ent analysis (PCA), correlation, and dominance analysis were employed for d escribing the seasonal dynamics of diatom assemblages and estimating the co rrelation between diatom distribution and the physico-chemical parameters. All periphytic communities were compared by PCA, MANOVA and Fisher's LSD mu ltiple comparison test. Ionic strength and eutrophication were the major ab iotic factors affecting diatom distribution in the epilithon, epiphyton, ep ipelon and epipsammon. Current velocity had an important influence on the d iatom assemblages from the epilithon and epiphyton. Epilithon showed the lo west correlation with most of the environmental factors and had significant ly lower species diversity than epiphyton, epipelon and epipsammon. Multiva riate analysis of the diatom data suggested that in all benthic habitats of the Mesta River seasonal replacement of diatom assemblages was controlled by the water chemistry rather than substratum, current velocity or discharg e. The oligotrophic, mesotrophic and eutrophic diatom communities in the Me sta River comprised early-, mid- and late-successional colonizers respectiv ely. Multiple comparisons of all periphytic communities showed that habitat specificity was positively correlated with current velocity.