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Comparison of the depth where Planktothrix rubescens stratifies and the depth where the daily insolation supports its neutral buoyancy
Author(s) -
Walsby Anthony E.,
Ng Gabrielle,
Dunn Catherine,
Davis Phillip A.
Publication year - 2004
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.2004.01020.x
Subject(s) - stratification (seeds) , buoyancy , neutral buoyancy , insolation , irradiance , hypolimnion , environmental science , thermal stratification , atmospheric sciences , bloom , ecology , biology , geology , nutrient , botany , eutrophication , climatology , physics , thermocline , seed dormancy , germination , quantum mechanics , dormancy , fishery
Summary• Comparisons were made of the depths where the cyanobacterium Planktothrix rubescens stratified in lakes and the depths where the daily insolation supported neutral buoyancy of the organism. • The percentage of filaments floating and sinking were measured in cultures grown under light : dark cycles at different irradiances. Q n , the daily insolation for neutral buoyancy, was determined as that at which 50% of the filaments were floating, averaged over the 24‐h period. • For P. rubescens 9316 from Lake Zürich, Q n was 0.28 mol m −2 ; during the summer period of stratification in Lake Zürich, the neutral buoyancy depth ( z n ) at which this insolation occurred varied between 5 and 14 m, depending on cloud cover and light attenuation. The weekly mean depth of the Planktothrix population maximum ( z p ) was usually within 1 m of the mean z n . For P. rubescens 9972 from Blelham Tarn, Q n was 0.51 mol m −2 ; during the stratified period in Blelham Tarn, z n varied between 2.3 and 6.2 m, also similar to z p ; the shallower stratification depth is explained by the steeper light attenuation. • The depth at which Planktothrix stratifies in lakes is therefore explained by buoyancy regulation in relation to the irradiance. Metalimnetic stratification occurs only when z n exceeds the mixed depth, z m ; when z m > z n , the organism becomes entrained in the surface mixed layer.