L. Hably szerk.: Studia Botanica Hungarica 23. 1992 (Budapest, 1992)

Buczkó, Krisztina; Ács, Éva: Preliminary studies on the periphytic algae in the branch-system of the Danube at Cikolasziget (Hungary)

Constancy was 4 and 5 in the following species (11%): 5: Lyngbya limnetica, Achnanthes minutissima, Cyclotella meneghiniana, Cymbella minuta, Fragilaria ulna, Gomphonema parvulum, Navicula cryptocephala, Thalassiosira pseudonana, Stigeoclonium tenue, 4: Pseudanabaena catenata, Cocconeis pediculus, Cymbella affinis, Fragilaria ulna var. acus, Gomphonema truncatum, Navicula rhynchocephala, Nitzschia linearis, N palea, Stephanodiscus hantzschii f. tenuis, S. invisitatus, Characium ensiforme. These species were constant, subconstant (JAKUCS 1981). The majority (76%) of the species was accidental (C= 1 or 2). Mainly diatoms were found abundantly in the samples (except on Carex acutiformis, where green algae were predominant). The high number of green algal taxa, and their low rate of abundance were characteristic. The blue-green algae and others were not important. Achnanthes minutissima was the predominant taxon on each host in the 1st, 3rd, and 4th sampling point. Cymbella minuta had more than 5% relative abundance on the 1st, 3rd and 4th sampling point, Stigeoclonium tenue on 1st and 4th point, Nitzschia fonticola and Fragilaria ulna on the 1st sampling point. The species composition of the predominant taxa was very variable in the 2nd sampling point: substrates taxon D% green reed Achnanthes minutissima 34.01 green reed Fragilaria brevistriata 33.75 Carex acutiformis Characium ensiforme 67.42 Carex acutiformis Achnanthes minutissima 20.05 Fragilaria brevistriata 8.02 Myriophyllum vert. Fragilaria brevistriata 24.63 Achnanthes minutissima 15.67 Fragilaria ulna 13.18 Characium ensiforme 5.0 twig before the rise Achnanthes minutissima 26.5 Fragilaria pinnata 13.75 Characium ensiforme 9.5 Fragilaria ulna var. acus 6.75 Epithemia sorex 6.25 twig after the rise Nitzschia fruticosa 40.25 Achnanthes lanceolata 10.25 The constant and dominant species were (constancy 5, dominancy 5% at least in one sample): Achnanthes minutissima, Cymbella minuta, Fragilaria ulna, Stigeoclonium tenue. It is interesting that Achnanthes minutissima, the characteristic taxon of the periphyton of the investigated branch-system, was found only in negligible numbers on the twig which was collected after the rise. The samples collected by us from the branch-system of the Danube at Cikolasziget seem to originate from an intermediate community of periphytic algae. This