Daphnia versus Copepod Impact on Summer Phytoplankton: Functional Compensation at Both Trophic Levels

• Published in: Oecologia 2003-05, Vol.135 (4), p.639-647
• Main Authors: Sommer, Ulrich, Sommer, Frank, Santer, Barbara, Eckart Zöllner, Jürgens, Klaus, Colleen Jamieson, Boersma, Maarten, Klaus Gocke
• Format: Article
• Language: English
• Subjects: Algae; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Autoecology; Biological and medical sciences; Biomass; Carbon Radioisotopes - metabolism; Chlorophyll - metabolism; Community Ecology; Copepoda; Copepoda - growth & development; Copepoda - physiology; Daphnia - growth & development; Daphnia - physiology; Daphnia galeata; Daphnia hyalina; Density; Feeding Behavior - physiology; Food Chain; Fresh Water; Fresh water ecosystems; Freshwater; Fundamental and applied biological sciences. Psychology; Germany; Limnology; Mesotrophic lakes; Phytoplankton; Phytoplankton - growth & development; Plankton; Population Density; Population Dynamics; Primary production; Primary productivity; Protozoa. Invertebrata; Seasons; Seeding; Species composition; Synecology; Trophic levels; Zooplankton; Zooplankton - growth & development; Zooplankton - physiology
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-003-1214-7

Here we report on a mesocom study performed to compare the top-down impact of microphagous and macrophagous zooplankton on phytoplankton. We exposed a species-rich, summer phytoplankton assemblage from the mesotrophic Lake Schöhsee (Germany) to logarithmically scaled abundance gradients of the microphagous cladoceran Daphnia hyalina×galeata and of a macrophagous copepod assemblage. Total phytoplankton biomass, chlorophyll a and primary production showed only a weak or even insignificant response to zooplankton density in both gradients. In contrast to the weak responses of bulk parameters, both zooplankton groups exerted a strong and contrasting influence on the phytoplankton species composition. The copepods suppressed large phytoplankton, while nanoplanktonic algae increased with increasing copepod density. Daphnia suppressed small algae, while larger species compensated in terms of biomass for the losses. Autotrophic picoplankton declined with zooplankton density in both gradients. Gelatinous, colonial algae were fostered by both zooplankton functional groups, while medium-sized (ca. 3,000 μ m3), non-gelatinous algae were suppressed by both. The impact of a functionally mixed zooplankton assemblage became evident when Daphnia began to invade and grow in copepod mesocosms after ca. 10 days. Contrary to the impact of a single functional group, the combined impact of both zooplankton groups led to a substantial decline in total phytoplankton biomass.