The ecology of algae in the Moruya river, Australia

Abstract

The standing crop of benthic and planktonic algae in the Moruya River, Australia, was, in general, low compared with values given for northern hemisphere rivers. Diatoms always accounted for more than 90% of the algae on the sediments with the most common species being typical of holarctic flora. The relative abundance of each of six predominant taxa was similar at the three sampling localities and did not show marked seasonal variation. However, Gomphonema spp. contributed a relatively greater number in the downstream area whereas Cocconeis placentula Ehr. was comparatively more abundant upstream. The highest standing crop (1.47 × 10⁶ cells/cm²) was found downstream and in the calmest part of the river between January and March, coincident with maximum water temperatures. A true phytoplankton succession comprising filamentous chlorophytes, Scenedesmus, Melosira varians Ag., Dactylococcopsis, Eudorina and Merismopedia was observed at the most downstream site during the spring and summer, with a maximum standing crop of 126.7 × 10³ cells/litre being attained in December. The gut of larval lampreys > 100 mm contained large numbers (44,000–525,000 cells) of algae. Scenedesmus and Dactylococcopsis occurred much more frequently in the gut than in either the sediment or water, but the reverse was true for filamentous algae.