DETECTION AND ANALYSIS OF UNUSUAL EVENTS IN LONG-TERM ZOOPLANKTON ANDNEKTON DATA SETS FROM NORTH INLET ESTUARY, SOUTH-CAROLINA, USA

Unusual events and disturbances are important sources of variability i n ecological data sets, but methods for their detection and analysis a re not readily available. We have adapted widely-used quality control methods to identify and quantify unusual events in ten-year-long data sets from the relatively pristine North Inlet Estuary, South Carolina, USA.-Seasonal patterns and long-term trends were first removed from b iweekly zooplankton and nekton abundance and corresponding water tempe rature and salinity data using nonparametic smoothing algorithms. The Shewhart Control Chart Method, a quantitative technique used for quali ty control in industrial manufacturing processes, was used to define f our types of events according to intensity and duration. Deviations of data points from the precalculated mean were determined and, based on the Shewhart criteria, unusual events were identified. Events were un common for most of the 39 zooplankton and nekton variables tested. Tim ing and frequency of events were irregular within and among years. The coincidental occurrence of biological and physical events was rare; h owever, unusually high or low abundances of some taxa occurred during some extreme salinity and temperature events. In general, a high degre e of independence among taxa was indicated. Results of the analyses pr ovide new insights into the ecological significance of stochasticity i n the dynamic estuarine ecosystem. The Shewhart Control Chart Method i s a relatively simple and unique procedure for investigating atypical variation, and its application may be useful for understanding the rol e of unusual events in determining long-term change in both natural an d altered ecosystems.