KOSMOS 2020 Peru mesocosm study on ecosystem responses to different light and upwelling intensities: d15N and trophic level for fish, meso-zooplankton and particulate organic matter

Trophic structure of plankton communities during the mesocosm experiment in the Peruvian upwelling system near Lima from February-April 2020. Light (ambient = high vs. reduced = low) was manipulated from the beginning (day 0) and upwelling (0 to 60% deep water addition) two weeks into the experiment (day 13). Larvae Peruvian anchovy (Engraulis ringens, 22 days-post-hatch) and chita (Anisotremus scapularis, 44 days-post-hatch) reared in the laboratory were introduced shortly after (day 19). Meso-zooplankton were sampled with small nets at several points in time and the fish once with a large net at the end of the experiment (day 36). Groups of whole meso-zooplankton individuals and muscle tissue of single fish individuals were analysed for C, N and δ15N. Most fish had reached the late larval or early juvenile stage by that time. Particulate organic matter was monitored throughout the entire experiment in 2-day intervals. Trophic level of fish and zooplankton was approximated using particulate organic matter corrected for its heterotrophic component as autotroph baseline and a discrimination factor of 3.4. Methodological details in Goldenberg et al. and Thielecke et al. (manuscripts in progress).