� 1999, by the American Society of Limnology and Oceanography, Inc. Diffusive boundary layers, photosynthesis, and respiration of the colony-forming plankton algae, Phaeocystis sp.

• Main Authors: Helle Ploug, Willem Stolte, Bo Barker Jørgensen, Thanks Paul, Wassmann H. Ploug
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: a research cruise on R; Barents Sea
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.419.1953; http://www.aslo.org/lo/toc/vol_44/issue_8/1949.pdf

Diffusive boundary layers, photosynthesis, and respiration in Phaeocystis colonies were studied by the use of microelectrodes for oxygen and pH during a bloom in the Barents Sea, 1993, and in the Marsdiep, Dutch North Sea, 1994. The oxygen microenvironment of a Phaeocystis colony with a mean diameter of 1.4 mm was mapped from 346 O2 measurements and showed gradients of oxygen concentration in the water phase up to 1 mm distance from the colony surface. The effective diffusive boundary layer was 0.4–0.9 mm thick. Oxygen concentrations inside colonies reached 180 % of the bulk water, and pH increased up to 0.4 units when measured in light at saturating intensities (�90 �mol photons m�2 s�1). The respiration in the dark was low, resulting in a 6 % lowering in oxygen concentration and 0.04 units lowering in pH inside colonies, compared to the bulk water phase. Such colonies were net heterotrophic communities at light intensities up to 10 �mol photons m�2 s�1. A week later, colonies were net heterotrophic at light intensities up to 80 �mol photons m�2 s�1. The effective diffusion coefficient for oxygen in the gelatinous colonies was not significantly different from that in sea water. The physical properties of sea water shift dramatically from a centimeter scale down to a micrometer scale in the ocean, as the viscous forces become predominant with decreasing