Fig 1.
Images of organism classes (obtained with the ZooScan method) that made up a significant portion of overall biomass.
A: Large copepods (Pseudocalanus acuspes), B: small copepods (likely copepodites), C: copepod nauplii, D: Coscinodiscus sp. cells, E: Hydromedusae. Scale bar is identical for all panels.
Fig 2.
Temporal development of size distribution in the control mesocosms (average) over the course of the experiment.
(A): normalized particle size spectrum, (B) weighted biomass spectrum. Note that particle diameter (ESD), as well as abundance and biomass are displayed on a log10-scale. (C) and (D): same as in (A) and (B), respectively, but focusing on t1 and t57. Shaded area denotes range of replicate mesocosms. Note that biomass in (D) is shown on a semi-log scale (i.e. linear y-axis) and not on a log-log-scale as in (B).
Fig 3.
Average contribution of copepods and Coscinodiscus sp. to the biomass size distribution in the control mesocosms.
(A) initial conditions (t1). (B) during period of maximum biomass (t57). Shaded area denotes range of replicate mesocosms.
Table 1.
Temporal changes in plankton community size structure.
Average biomass of Coscinodiscus sp. and different size classes of copepods in the control mesocosms on t1 and t57 (± standard error, SE).
Fig 4.
Size structure of the copepod community (including nauplii) in the mesocosms (average of 5 mesocosms in the control treatment).
(A) normalized abundance spectrum and (B) weighted biomass spectrum. Shaded area denotes range of replicate mesocosms.
Fig 5.
CO2 effects on particle size spectra.
Comparison of normalized abundance spectrum (A) and weighted biomass spectrum (B) in the control (blue) and high CO2 mesocosms (red) on day t57. Shaded area denotes range of replicate mesocosms and asterisks indicate a statistically significant effect of CO2 on the respective size class (p<0.05).
Fig 6.
CO2 effects on the plankton community.
CO2-related differences in biomass of copepods and nauplii (A,B) and Coscinodiscus sp. (C,D) in the control (blue) and high CO2 mesocosms (red) on day t57. Shown are the size distribution of biomass in weighted biomass-size spectra (A,C) and box plots for overall biomass (B,D). Shaded area denotes range of replicate mesocosms and asterisks in panel A and C indicate a statistically significant effect of CO2 on the respective size class (p < 0.05). Tests for statistical significance of total biomass in the respective groups (B,D) yielded p-values of p = 0.06 (copepods) and p = 0.10 (Coscinodiscus).
Table 2.
CO2 effects on the plankton community.
Average biomass of Coscinodiscus sp. and different size classes of copepods in the mesocosms under ambient conditions and under high CO2 on day t57. Shown is the average of five mesocosms (± standard error, SE).
Fig 7.
Evaluation of image-based method.
Comparison of biomass development estimated from flow cytometry and Zooscan (A) with measurements of particulate organic carbon (POC) (B) in the control (blue) and high CO2 mesocosms (red). Shaded areas denote range of replicates. (C) Scatter plot comparing biomass estimated in this study with measured POC for all mesocosms and sampling days (n = 140, R2 = 0.83)