Fig 1.
Four potential scenarios how phytoplankton bloom development could be altered by ocean acidification explained with the example of chla concentration.
Blue and red lines illustrate control and “treatment”, respectively. (A) Change in bloom amplitude. (B) Change in bloom timing. (C) Change in bloom amplitude and timing. (D) Change in bloom pattern.
Fig 2.
Red and blue lines display the average of five high and five ambient CO2 mesocosms, respectively. Shaded areas represent standard deviations from means. Vertical grey lines (Roman numbers I to IV) separate the four experimental phases.
Fig 3.
Development of phytoplankton groups quantified by flow cytometry and filter counts.
Red and blue lines display the average of five high and five ambient CO2 mesocosms, respectively. Shaded areas represent standard deviations from means. Data are displayed on linear (A-H) and logarithmic y-axis (I-P). Note: the exponent in A-H after a group name needs to be multiplied with the y-axis numbering (e.g. 5 Syn x 104 → 50000 Synechoccocus cells mL-1). Vertical grey lines (Roman numbers I to IV) separate the four experimental phases.
Fig 4.
Development of phytoplankton classes based on CHEMTAX pigment taxonomy.
Red and blue lines show the average of five high and five ambient CO2 mesocosms, respectively. Shaded areas represent standard deviations from means. The y-axis shows the amount of chla contributed by each class. Vertical grey lines (Roman numbers I to IV) separate the four experimental phases.
Fig 5.
Relative chla contribution of the 8 phytoplankton classes determined with CHEMTAX to bulk chla.
(A) Average of the control mesocosms. (B) Average of the high CO2 mesocosms. Vertical grey lines (Roman numbers I to IV) separate the four experimental phases. Chryso = Chrysophyceae; Cyano = Cyanophyceae; Dino = Dinophyceae; Pras = Prasinophyceae; Chloro = Chlorophyceae; Crypto = Cryptophyceae; Prym = Prymnesiophyceae; Dia = Diatoms.
Fig 6.
SEM pictures of important pico- and nanophytoplankton species during the two major phytoplankton blooms.
A) Representative overview picture from M1 on day 35 including Arcocellulus sp., Minidiscus sp., and Tetraparma sp. (all three are silicifying species). B) Three Minidiscus sp. cells without organic membrane cover in M6 on day 35. C) Minidiscus sp. without organic membrane cover in M4 on day 27. D) Arcocellulus sp. in M1 on day 27 E) Two Tetraparma sp. cells in M1 on day 35. F) Three spherical cells (probably picophytoplankton) in M1 on day 35. Yellow scale bars are 3 μm long.
Table 1.
Summary of statistical results.
The temporal development of phytoplankton was analyzed by means of GAMM. A CO2 effect was detected when the GAMM model with the best fit (highest R2 value) accounted for a CO2 dependency of the phenology. In the case of Nano I a CO2 effect was detected by the GAMM analysis but not considered further due to an unsatisfactory model fit.