Phytoplankton structure and dynamics at a daily temporal scale: Response to the thermal overturn
Rojo, Carmen; Alvarez-Cobelas, Miguel
published: Jul 9, 2001
ArtNo. ESP141015104001, Price: 29.00 €
We examined phytoplankton structure and dynamics at the daily scale in a temperate lake during overturn (75 days). Fifty species of phytoplankton inhabited the oligo-mesotrophic Las Madres Lake (Spain) throughout the study period, demonstrating different strategies and resulting distribution patterns. The distribution of dominant taxonomic groups changed through the overturn, varying within four dendrogram sets of dates. Biomass was affected by changes in species composition as a result of the overturn process (the rate of change been markedly greater at the beginning and end). Autogenic mechanisms in the density of the main algae were highlighted by the diversity. The diversity index trajectory changed at start of overturn and in the middle of the complete mixing period. A Principal Components Analysis showed four different groups of dates, achieved by overturn process and by endogenous changes in the unperturbed period. Time series analyses (auto- and cross-correlations) showed delays of between a few days to some weeks, depending on species strategies (body size-related) and changes in the biomass trajectory at three weeks. Therefore, four alternate persistent states or alternate structures of phytoplankton were observed and described at the daily scale. We suggest that there were three mechanisms which drove the changes of state, namely overturn, grazing and competition. Population strategies may suggest how community structure changes at a down-scale level. Algal assemblage responses to daily changes were slower than population ones and showed greater persistence. The emergent assemblage behaviour was well exhibited by structural dynamics and biomass. In other words, changes in a lower level of ecological hierarchy (populations) led to some stability in an upper level (assemblage, community) when the latter was studied at the population time scale.