Photosynthesis is known to produce reactive oxygen species together with the transformation of light into biochemical energy. To fill the gap of the knowledge on the protective antioxidant network of microalgae, a series of experiments to explore the role of spectral composition and intensity of light in the modulation of the photodefence mechanisms developed by the coastal diatom Skeletonema marinoi were performed. The modulation of the total phenolic content, ascorbic acid and the enzymes glutathione reductase, catalase, ascorbate peroxidase and superoxide dismutase together with xanthophyll cycle and non-photochemical quenching in response to variations in the light environment were analysed. Most of the enzymes' activity was promptly affected by the red light. Yet, the monochromatic high intensity blue light enhanced the synthesis of total phenolic content and ascorbic acid in parallel to the xanthophyll cycle activity. This study reveals the dual effects of spectral composition and intensity of light on the modulation of photoprotective mechanisms. Diatoms developed a complementary and/or alternative tuning processes to cope with the variable light environment they experience in the water column. They also provided valuable insights into light manipulation regimes for diatom cultivation that will help to maximize production of bioactive molecules.

The equations used to account for the temperature dependence of biological processes, including growth and metabolic rates, are the foundations of our predictions of how global biogeochemistry and biogeography change in response to global climate change. We review and test the use of 12 equations used to model the temperature dependence of biological processes across the full range of their temperature response, including supra‐ and suboptimal temperatures. We focus on fitting these equations to thermal response curves for phytoplankton growth but also tested the equations on a variety of traits across a wide diversity of organisms. We found that many of the surveyed equations have comparable abilities to fit data and equally high requirements for data quality (number of test temperatures and range of response captured) but lead to different estimates of cardinal temperatures and of the biological rates at these temperatures. When these rate estimates are used for biogeographic predictions, differences between the estimates of even the best‐fitting models can exceed the global biological change predicted for a decade of global warming. As a result, studies of the biological response to global changes in temperature must make careful consideration of model selection and of the quality of the data used for parametrizing these models.

Oxygen toxicity is a problem in diving which can have fatal consequences in the water. When divers use closed-circuit oxygen rebreathing apparatus they are taking only oxygen 100% and this hyperoxic exposure increases the generation of reactive oxygen species (ROS) in biological tissues. The objective of the present study is to evaluate the effects of hyperoxia on biomarkers of oxidative stress in closed-circuit oxygen military divers. Fifteen professional divers of Spanish Navy Diving Centre participated in a training program which consisted of one-hour immersion at seven metres of depth breathing oxygen 100% with closed-circuit oxygen rebreathing apparatus. The training went on two or three times per week for the first six weeks and once a week for the last six weeks. Serum total antioxidant status (TAS), levels of glutathione peroxidase (GPx), nitrates (NO3(-)) and urinary concentrations of 15-isoprostane F2t were measured. The results show that TAS decreased significantly after 6 weeks (mean 1.38 versus 1.23 mmol/l), with a slight increase at the end (mean 1.31 mmol/l). GPx and F2-isoprostanes were significantly lower after 6 and 12 weeks and NO3(-) was significantly lower after 6 weeks and remained unchanged until the end. In summary, professional divers who use closed-circuit apparatus and therefore breathe oxygen 100%, do not suffer an important oxidative hyperoxia-induced stress, probably due an adaptive process after hyperoxia. The age and good physical form of the subjects studied could probably enhance the adaptive process to hyperoxia.

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