Diffusion or advection? Mass transfer and complex boundary layer landscapes of the brown algaFucus vesiculosus

Abstract

The role of hyaline hairs on the thallus of brown algae in the genus Fucus is long debated and several functions have been proposed. We used a novel motorized set-up for two-dimensional and three-dimensional mapping with O 2 microsensors to investigate the spatial heterogeneity of the diffusive boundary layer (DBL) and O 2 flux around single and multiple tufts of hyaline hairs on the thallus of Fucus vesiculosus. Flow was a major determinant of DBL thickness, where higher flow decreased DBL thickness and increased O 2 flux between the algal thallus and the surrounding seawater. However, the topography of the DBL varied and did not directly follow the contour of the underlying thallus. Areas around single tufts of hyaline hairs exhibited a more complex mass-transfer boundary layer, showing both increased and decreased thickness when compared with areas over smooth thallus surfaces. Over thallus areas with several hyaline hair tufts, the overall effect was an apparent increase in the boundary layer thickness. We also found indications for advective O 2 transport driven by pressure gradients or vortex shedding downstream from dense tufts of hyaline hairs that could alleviate local mass-transfer resistances. Mass-transfer dynamics around hyaline hair tufts are thus more complex than hitherto assumed and may have important implications for algal physiology and plant -microbe interactions.

Abiotic and biotic interactions in the diffusive boundary layer of kelp blades create a potential refuge from ocean acidification

“…However, the presence of the bryozoan layer increased the thickness of the DBL in all the conditions by creating their own DBL in addition to the kelp's one, essentially as a small canopy boundary layer (Cornwall, Pilditch, et al, 2015;Cornwall, Revill, et al, 2015). This phenomenon has also been observed on Fucus species where the presence of hyaline hairs increased the DBL thickness compared to hairless thalli (Lichtenberg, Nørregaard, & Kühl, 2017;Spilling et al, 2010). The explanation is that small-scale (μm-mm) surface topographical features such as corrugations, the presence of hyaline hairs or the cilia of bryozoans likely reduce the roughness Reynold's number Hurd, Stevens, Laval, Lawrence, & Harrison, 1997;Lichtenberg et al, 2017) or create a local depression (Wangpraseurt et al, 2012), thus increasing the DBL thickness.…”

“…This phenomenon has also been observed on Fucus species where the presence of hyaline hairs increased the DBL thickness compared to hairless thalli (Lichtenberg, Nørregaard, & Kühl, ; Spilling et al., ). The explanation is that small‐scale (μm–mm) surface topographical features such as corrugations, the presence of hyaline hairs or the cilia of bryozoans likely reduce the roughness Reynold's number (Hurd & Pilditch, ; Hurd, Stevens, Laval, Lawrence, & Harrison, ; Lichtenberg et al., ) or create a local depression (Wangpraseurt et al., ), thus increasing the DBL thickness. These engineering factors, flow velocity and the presence of bryozoans, are, therefore, not only able to affect the thickness of the DBL but also can directly and/or indirectly impact the chemical gradients occurring therein.…”

Radiative Energy Budgets of Phototrophic Surface-Associated Microbial Communities and their Photosynthetic Efficiency Under Diffuse and Collimated Light

“…The more variable DBL thickness in the coral sediment varied independently of irradiance and was most likely a result of the heterogeneous surface topography (Figure 4). A detailed mapping of the DBL landscape was beyond the scope of this study but, we estimate that the mass transfer between the sediment and overlying water was not influenced by turbulences which would have been evident as non-linear concentration gradients between sediment surface and bulk water (Lichtenberg et al, 2017). At incident irradiances >200 μmol photons m −2 s −1 the O 2 productive zone was stratified under both diffuse and collimated light, with an O 2 concentration maximum of ~600% air saturation ~1.7 mm below the sediment surface (Figure 4).…”

Strong leaf surface basification and CO2limitation of seagrass induced by epiphytic biofilm microenvironments

“…Figures 3 and S2) is likely a result of the biofilm heterogeneity as seen on Figure 1, where a thicker and more fluffy biofilm surface caused a more heterogeneous DBL landscape (see also Lichtenberg, Nørregaard, & Kühl, 2017). However, DBL characteristics of epiphytic biofilms were not used in the calculations of leaf surface level gas fluxes, which only entailed microprofile measurements in the denser, more homogeneous base biofilm on the seagrass leaf surface.…”