Intensive Aggregate Formation with Low Vertical Flux During an Upwelling-Induced Diatom Bloom

The surfaces of most pelagic diatoms are sticky at times and may therefore form rapidly settling aggregates by physical coagulation. Stickiness and aggregate formation may be particularly adaptive in upwelling systems by allowing the retention of diatom populations in the vicinity of the upwelling c...

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Bibliographic Details
Published in:Limnology and oceanography 1998-01, Vol.43 (1), p.104-116
Main Authors: Kiorboe, Thomas, Tiselius, Peter, Mitchell-Innes, Betty, Jorgen L. S. Hansen, Visser, Andre W., Mari, Xavier
Format: Article
Language:English
Subjects:
Aggregation
anchor station
Animal and plant ecology
Animal, plant and microbial ecology
Bacillariophyceae
Biological and medical sciences
Biological Sciences
Biologiska vetenskaper
Buoyancy
Cell aggregates
Chaetoceros
Coagulation
Copepoda
Diatoms
Ecology
Ecology, environment
Ecosystems
Ekologi
Fundamental and applied biological sciences. Psychology
german bight
Life Sciences
Marine
marine snow
Noctiluca scintillans
Phytoplankton
phytoplankton blooms
Plankton
red tide
Sea water
Sea water ecosystems
short-term variability
Size distribution
southern benguela
spring bloom
Synecology
Upwelling water
water column
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Summary:The surfaces of most pelagic diatoms are sticky at times and may therefore form rapidly settling aggregates by physical coagulation. Stickiness and aggregate formation may be particularly adaptive in upwelling systems by allowing the retention of diatom populations in the vicinity of the upwelling center. We therefore hypothesized that upwelling diatom blooms are terminated by aggregate formation and rapid sedimentation. We monitored the development of a maturing diatom (mainly Chaetoceros spp.) bloom in the Benguela upwelling current during 7 d in February. Chlorophyll concentrations remained consistently high during the observation period (!sim 500 mg Chl m-2) and phytoplankton grew at an average specific rate of 0.25 d-1. The diatom were extraordinarily sticky, with stickiness coefficients of up to 0.40, which is the highest ever recorded for field populations. Combined with estimates of turbulent shear in the ocean such stickiness coefficients predict very high specific coagulation rates (0.3 d-1). In situ video observation demonstrated the occurrence of abundant diatom aggregates with surface water concentrations between 1,000 and 3,000 ppm. Despite the very high concentration of aggregates, vertical fluxes of phytoplankton were very low, with fractional losses$
ISSN:0024-3590
1539-607X
1939-5590
1539-6088
DOI:10.4319/lo.1998.43.1.0104