The effects of rain on the erosion threshold and biogeochemical properties of intertidal sediments

The effects of simulated rain on the erosion threshold and biogeochemical properties of cores of muddy intertidal sediments were measured. Rain was simulated with a trailer-mounted device that produced rain with an intensity and drop size similar to that of natural rain. Erosion thresholds were measured with a cohesive strength meter (CSM) and sediment samples for analysis of the biogeochemical properties of the sediment were collected using the cryogenic contact-core technique. Rain caused significant disruption of the sediment surface, often resulting in significantly lower erosion thresholds and increased relative erosion rates. The removal of unconsolidated surface sediments and the revealing of deeper more consolidated sediments, however, caused an increase in the measured erosion threshold and a reduction in erosion rate in some treatments. The biogeochemical properties of the sediment were significantly altered by even a short duration of rain (5 min). Bio-dependent properties such as the amount of chlorophyll a and carbohydrates were generally decreased by rain. The presence of a visible biofilm did not significantly mediate the effects of rain on erosion thresholds, in contrast to their ability to significantly reduce erosion by tidal flows

Decision-making of the benthic diatom Seminavis robusta searching for inorganic nutrients and pheromones

Microorganisms encounter a diversity of chemical stimuli that trigger individual responses and influence population dynamics. However, microbial behavior under the influence of different incentives and microbial decision-making is poorly understood. Benthic marine diatoms that react to sexual attractants as well as to nutrient gradients face such multiple constraints. Here, we document and model behavioral complexity and context-sensitive responses of these motile unicellular algae to sex pheromones and the nutrient silicate. Throughout the life cycle of the model diatom Seminavis robusta nutrientstarved cells localize sources of silicate by combined chemokinetic and chemotactic motility. However, with an increasing need for sex to restore the initial cell size, a change in behavior favoring the attraction-pheromone-guided search for a mating partner takes place. When sex becomes inevitable to prevent cell death, safeguard mechanisms are abandoned, and cells prioritize the search for mating partners. Such selection processes help to explain biofilm organization and to understand species interactions in complex communities

The Peculiar Features of Non-Photochemical Fluorescence Quenching in Diatoms and Brown Algae

International audienceDiatoms and brown algae are major contributors to marine primary production. They arebiologically diverse, with thousands of different species, and are extremely successful, occupyingalmost every marine ecosystem ranging from the coastal-estuarine to deep-sea regions.Their ecological success is based in part on their ability to rapidly regulate photosynthesis inresponse to pronounced fluctuations in their natural light environment. Regulation of light excessive energy as heat. Thermal dissipation of excitation energy is assessed as non-photochemicalquenching of chlorophyll a fluorescence (NPQ). NPQ depends strongly on theconversion of xanthophylls: diadinoxanthin (Dd) to diatoxanthin (Dt) in the Dd-Dt cycle ofdiatoms and violaxanthin (V) to zeaxanthin (Z), via the intermediate antheraxanthin (A), inthe VAZ cycle present in brown algae. Xanthophyll cycle (XC)-dependent thermal energydissipation underlying NPQ represents one of the most important photoprotection mechanismsof diatoms and brown algae. In the present chapter, we review the biochemistry of XCenzymes with a special focus on co-substrate requirements and regulation of enzyme activity.In addition, we present a new model for the structural basis of XC-dependent NPQ indiatoms based on the latest experimental findings. In the last section, we highlight the importanceof XC-dependent photoprotection for the ecological success of diatoms and brownalgae in their natural environments