2014 Volume 14 Issue 1 Pages 37-58
We investigated the algae assemblages growing on the stone in the small stream near Standing Stone, southwestern part of the Pomano Island, the main island of Orkney Islands. We found one taxon of blue-green alga, 35 taxa of diatoms and 5 taxa of green algae. The cell density of the epilithic algae is 67,480 cells/mm^2. The dominant species are composed of diatom taxa, Nitzschia palea, Cocconeis pediculus, Achnanthes minutissima, Fragilaria capucina, Navicula gregaria and Nav. lanceolata. The samples profusely contained dead cells of diatoms and the relative frequency was up to 39.8%. The algal assemblages in the sample are characterized by high cell density, active growth of euryhaline species as Diatoma moniliformis, Navicula gregaria, and Synedra pulchella var. pulchella, and dominance by tolerant species of organic pollution as Cyclotella meneghiniana, Gomphonema parvulum, Nit. palea, Syn. ulna, Ankistrodesmus falcatus, Chlamydomonas sp. and Scenedesmus acutus. Furthermore, although the number of the taxa found in the sample was relatively large, only two circumboreal algae taxa were found, i.e., Cymbella hybrida var. lanceolata and Stauroneis acidolinatopsis.
