USE OF ALGAE FOR ESTABLISHING CRITERIA FOR PROTECTING AND RESTORING AQUATIC ECOSYSTEMS.

R.J. Stevenson. Department of Zoology, Michigan State University, East Lansing, Michigan 48864

Deviations in algal attributes between reference and test sites can be used to establish environmental criteria using two approaches, one based on frequency distribution of variables at reference or all sites and another based on response of algal attributes to changes in environmental conditions. The former and latter approaches complement one another, even though they can provide different information. For example, the total phosphorus (TP) criteria for Mid-Atlantic streams based on variability in P conditions among reference sites is usually similar to P criteria based on most algal responses to P enrichment. However, P criteria based on algal responses can vary greatly depending upon the attributes studied. Ecological models predict that population characteristics should be more sensitive than community and ecosystem attributes. Predictable progression in ecological degradation would provide a basis for standardizing approaches of environmental assessment. In the Everglades, the TP concentration causing changes in species composition is lower than P concentration causing a change in biomass. This predictable difference in sensitivity of population and community responses was not observed in large surveys of streams. The relatively unpredictable responses in streams may be due to highly variable conditions among multiple streams or different species responses among types of ecosystem.