EFFECT OF SAND MOVEMENT ON THE GROWTH OF BENTHIC DIATOMS

The effect of sand motion on the growth of two cultures of the benthic diatom species Surirella ovata and Navicula digitoradiata and a mixed population of benthic diatoms was studied under experimental conditions. During the first few days of the experiments there was an important fall in cell numbers as a result of sand movement, whereas the reference cultures kept under calm standard conditions for batch cultures grew exponentially. After this stage the cultures responded differently: S. ovata showed a further reduction of cell number whereas N. digitoradiata and the mixed populations showed recovery followed by clear growth. Micrographs show that the losses in cell numbers result from the cells being broken, presumably by collisions with sand grains. The results are discussed in relation to turbulent conditions in exposed parts of estuaries and to some properties of diatom species.