Primary production and size-fractionated structure of the Black Sea phytoplankton in the winter-spring period

• Published in: Marine ecology. Progress series (Halstenbek) 1991, Vol.73 (1), p.25-31
• Main Authors: Krupatkina, D. K., Finenko, Z. Z., Shalapyonok, A. A.
• Format: Article
• Language: English
• Subjects: Chlorophylls; Diatoms; Marine; Phytoplankton; Primary productivity; Respiration; Sea water; Seas; Seasons; Spring; Winter
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps073025

Basic photosynthetic characteristics determining the shift in phytoplankton species and size composition from coccolithophores and dinoflagellates to diatoms were investigated. The study revealed a slight seasonal decrease in the light utilization efficiency (αchl) from 0.078 to 0.056 mg C (mg chl a−1) h−1 (W m−2) from winter to early spring, as well as a small increase in the photosynthesis light saturation (Ik; 29.4 and 45.5 W m−2, respectively) and in the diurnal assimilatory number [DAN; 19.6 and 24.0 mg C (mg chl a)−1 d−1, respectively]. At the same time, respiration (R) fell drastically: in winter, when phytoplankton was dominated by dinoflagellates and coccolithophores, R was 29 % of maximum production (Pmax), while in spring, with diatoms dominating, R was 2.5 % of Pmax. Chlorophyll a concentration also showed a drastic increase: from 0.73 to 2.15 mg m−3 in the surface layer and from 20 to between 100 and 150 mg m−2 on an areal basis. These data suggest that the nearly 2-fold growth of primary production from winter to spring (275.2 ± 163.5 and 581.4 ± 232.4 mg C m−2 d−1, respectively) is accounted for by larger phytoplankton biomass and lower respiration. These changes were mainly brought about by an increase in diatoms: the increase of both production and chlorophyll a from winter to spring features an ever greater diatom contribution, reaching > 50 % in spring. A close relationship is suggested between the increase in primary production and the changes in the structure of seawater from winter to spring.