The evolution of organisms capable of oxygenic photosynthesis paralleled a long-term reduction in atmospheric CO₂ and the increase in O₂. Consequently, the competition between O₂ and CO₂ for the active sites of RUBISCO ribulose bisphosphate carboxylase/oxygenase became more and more restrictive to the rate of photosynthesis. In coping with this situation, many algae and some higher plants acquired mechanisms that use energy to increase the CO₂ concentrations (CO₂ concentrating mechanisms, CCMs CO₂ concentrating mechanism ) in the proximity of RUBISCO. A number of CCM variants are now found among the different groups of algae. Modulating the CCMs may be crucial in the energetic and nutritional budgets of a cell, and a multitude of environmental factors can exert regulatory effects on the expression of the CCM components. We discuss the diversity of CCMs, their evolutionary origins, and the role of the environment in CCM modulation.

Global increases in atmospheric CO₂ and temperature are associated with changes in ocean chemistry and circulation, altering light and nutrient regimes. Resulting changes in phytoplankton community structure are expected to have a cascading effect on primary and export production, food web dynamics and the structure of the marine food web as well the biogeochemical cycling of carbon and bio-limiting elements in the sea. A review of current literature indicates cell size and elemental stoichiometry often respond predictably to abiotic conditions and follow biophysical rules that link environmental conditions to growth rates, and growth rates to food web interactions, and consequently to the biogeochemical cycling of elements. This suggests that cell size and elemental stoichiometry are promising ecophysiological traits for modelling and tracking changes in phytoplankton community structure in response to climate change. In turn, these changes are expected to have further impacts on phytoplankton community structure through as yet poorly understood secondary processes associated with trophic dynamics.

SUMMARY: Analysis of data in the literature relating to microalgal adaptations to different photon flux densities indicates that different algal classes have significantly different light requirements for growth and photosynthesis. Although there is some variability within each class, dinoflagellates and blue‐green algae generally photosynthesize and grow best at low photon flux densities. Diatoms also tend to be able to grow at very low photon flux densities (growth for some species has been reported at less than 1 μE m⁻¹ s⁻²). Comparison of the photon flux densities at which photoinhibition occurs in dainoflagellates and diatoms suggests that the former often experience photoinhibition at comparatively low irradiances. In contrast, diatoms often can tolerate relatively high light environments. This tolerance of a large absolute range of photon flux densities may, in part, explain why diatoms are often associated with spring blooms. Green algae

The global environment is currently experiencing a period of significant change in climate as a result of human activities. Although the planet has experienced very significant variations in climate in the geological past, the rate at which the present changes are occurring is extraordinary. Anthropogenic influences have resulted in an enhancement of atmospheric carbon dioxide levels which will amount to a two- to threefold increase over the next century and this has already led to a measurable rise in global temperature. At the same time, chlorofluorocarbons are reacting with ozone in the stratosphere, a process that has led to appreciable enhancement of UV-B radiation (UVBR) fluxes to the earth's surface at high latitudes. This review addresses our present state of knowledge about the effects of enhanced carbon dioxide levels, elevated UVBR fluxes and higher temperatures on the ecophysiology of microalgae. We consider the potential interactions between these and other environmental factors, suc...

The literature, and previously unpublished data from the authors’ laboratories, shows that the δ13C of organic matter in marine macroalgae and seagrasses collected from the natural environment ranges from –3 to –35‰. While some marine macroalgae have δ13C values ranging over more than 10‰ within the thallus of an individual (some brown macroalgae), in other cases the range within a species collected over a very wide geographical range is only 5‰ (e.g. the red alga Plocamium cartilagineum which has values between –30 and –35‰). The organisms with very negative δ13C (lower than –30‰) are mainly subtidal red algae, with some intertidal red algae and a few green algae; those with very positive δ13C values (higher than –10‰) are mainly green macroalgae and seagrasses, with some red and brown macroalgae. The δ13C value correlates primarily with taxonomy and secondarily with ecology. None of the organisms with δ13C values lower than –30‰ have pyrenoids. Previous work showed a good correlation between δ13C values lower than –30‰ and the lack of CO2 concentrating mechanisms for several species of marine red algae. The extent to which the low δ13C values are confined to organisms with diffusive CO2 entry is discussed. Diffusive CO2 entry could also occur in organisms with higher δ13C values if diffusive conductance was relatively low. The photosynthesis of organisms with δ13C values more positive than –10‰ (i.e. more positive than the δ13C of CO2 in seawater) must involve HCO3- use.