MEPS 545:35-47 (2016)  -  DOI:

Light and O2 microenvironments in two contrasting diatom-dominated coastal sediments

Paulo Cartaxana1,*, Lourenço Ribeiro2,3, Johannes W. Goessling1, Sónia Cruz1,4, Michael Kühl1,5 

1Marine Biological Section, Department of Biology, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark
2Université de Nantes, Mer Molécules Santé EA2160, Faculté des Sciences et des Techniques, 44322 Nantes Cedex 3, France
3Centro de Ciências do Mar e Ambiente (MARE), Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
4Departamento de Biologia & CESAM - Centro de Estudos do Ambiente e do Mar, Universidade de Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
5Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Sydney, NSW 2007, Australia
*Corresponding author:

ABSTRACT: The close coupling of photosynthesis and light was studied in 2 contrasting diatom-dominated coastal sediments (sand and mud flats) using O2 microelectrodes and fiber-optic microprobes for scalar irradiance. The diatom community of the muddy sediment was composed almost exclusively of motile epipelic species, whereas in the sandy sediment similar contributions of epipsammic and epipelic diatoms were observed. The attenuation coefficient of scalar irradiance (K0) was significantly higher in the mud, where light was attenuated exponentially with depth from the sediment surface. In the sand, scalar irradiance levels increased in the first 0.1–0.2 mm due to high scattering and low absorption. Attenuation of scalar irradiance was highest for wavelengths of absorption by major diatom photopigments (chlorophylls and carotenoids). Higher areal and volumetric rates of O2 respiration were found in illuminated sediments than those in the dark, resulting from an increase in both O2 concentration and penetration depth and a direct stimulation of heterotrophic processes. A lower light acclimation index (Ek) was observed for the muddy sediment community, indicating lower light acclimation compared to the sandy sediment community. Areal and volumetric rates of photosynthesis were ~3 times higher in the muddy sediment. We conclude that higher photosynthetic rates in the finer sediment were determined by (1) a thinner and more densely populated photic zone, where the contribution of active photopigments to total light absorption relative to that of photosynthetically inactive components was higher, and (2) differences in diatom species composition and dominant life-strategies, specifically the capacity of cells to actively search for optimal light microenvironments in the fine-grained sediment.

KEY WORDS: Microsensors · Diatoms · Migration · Photosynthesis · Respiration · Scalar irradiance

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Cite this article as: Cartaxana P, Ribeiro L, Goessling JW, Cruz S, Kühl M (2016) Light and O2 microenvironments in two contrasting diatom-dominated coastal sediments. Mar Ecol Prog Ser 545:35-47.

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