Phytoplankton community structure in the lower reaches of a Mediterranean river (Aliakmon, Greece)

Phytoplankton communities from the lower reaches of the Aliakmon River, Gre ece, have been studied over a period of one year. Seasonal phytoplankton dy namics was described on the basis of its species composition and abundance, biomass and chlorophyll-a concentrations. Phytoplankton assemblages compri sed diatoms (mainly Cyclotella meneghiniana, Nitzschia palea and Fragilaria ulna), cyanobacteria (mainly Pseudanabaena limnetica, Aphanizomenon sp. an d Limnothrix cf. redekei) and green algae (various species of Scenedesmus a nd Chlamydomonas, Coelastrum microporum and Monoraphidimm contortum). Many benthic diatoms were also present. An important growth of euglenophytes was observed during summer, mainly Lepocinclis steinii, L. ovum, Euglena inter media, E. viridis and Phacus caudatus. The spring maximum of centric diatom s extended into the summer. The qualitative and quantitative composition of the phytoplankton is compared to communities of other European rivers. Wit h regard to phytoplankton assemblages, Aliakmon resembles more the relative ly fast-flowing, "individual-poor" European rivers. Its widely varying disc harge volume, turbidity and shallowness, seem to be the main factors contro lling phytoplankton communities in its lower reaches.