Effects of growth condition on succession patterns in tropical phytoplankton assemblages subjected to experimental eutrophication

Abstract

We isolated phytoplankton assemblages from five tropical lakes differing in environmental conditions and incubated them under different extreme growth conditions. Conditions were: under light with nutrient addition (L + N), under light with nutrient and organic carbon addition (L + N + OC), and in the dark with nutrient and organic carbon addition (N + OC). These were intended to simulate phytoplankton succession during early, intermediate and late eutrophication stages, respectively. Decreases in species diversity and richness in N + OC assays from all lakes, except the most eutrophic one, suggested consistent diversity and richness declines during late eutrophication stages. Declines in species diversity were generally caused by a stronger reduction in species richness than evenness, indicating that species exclusion is a more probable response to eutrophication than co-existence and dominance of strong competitors. Under N + OC conditions, the osmotrophic chlorophyte Chlamydomonas was generally dominant, indicating that this flagellate may prevail in late eutrophic communities in the tropical lakes studied. The L + N and L + N + OC assays did not differ from each other in species diversity, but exhibited differences in species composition and richness. This suggests that the changing role of the phytoplankton community in whole-lake matter fluxes during early eutrophication stages could be a more important research question, than predicting the community's diversity response in tropical lakes. © The Author 2013. Published by Oxford University Press. All rights reserved.