Freshwater diatom ecology: developing an experimental approach as an aid to interpreting field data

Abstract

The observational and experimental approaches to ecological studies are outlined and contrasted. Most studies involving benthic diatoms are still at the observational stage. Community analyses are interpreted in relation to physico-chemical variables, but without reference to the intrinsic growth characteristics of the species or to biological interactions. By allowing separate investigation of the effects of chosen variables under controlled conditions, culture studies permit field predictions to be tested and our understanding of the constraints on growth of particular species to be improved.

Results of culture experiments on four benthic diatom species grown under contrasting light, temperature, and pH regimes are presented and discussed in relation to their field distributions. Synedra ulna showed a positive response to both light and temperature; Meridion circulare was more sensitive to raised water temperature at higher light intensity; Pinnularia viridis and Eunotia exigua grew over wider ranges of temperature and pH than recorded from published data. The experimental results indicate that distribution data provide only partial information on ecological range; growth in the field may be constrained by one or more factors and their interactions.

Whereas analysis of field data is a correlative exercise, an experimental approach allows investigation of the physiological responses contributing to the survival of species and the demonstration of causal relationships.