There has been a good deal of interest in the potential of marine vegetation as a sink for anthropogenic C emissions ("Blue Carbon"). Marine primary producers contribute at least 50% of the world's carbon fixation and may account for as much as 71% of all carbon storage. In this paper, we analyse the current rate of harvesting of both commercially grown and wild-grown macroalgae, as well as their capacity for photosynthetically driven CO 2 assimilation and growth. We suggest that CO 2 acquisition by marine macroalgae can represent a considerable sink for anthropogenic CO 2 emissions and that harvesting and appropriate use of macroalgal primary production could play a significant role in C sequestration and amelioration of greenhouse gas emissions.

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It is well known that UV radiation can cause deleterious effects to the physiological performance, growth and species assemblages of marine primary producers. In this review we describe the range of interactions observed between these impacts of ultraviolet radiation (UVR, 280-400 nm) with other environmental factors such as the availability of photosynthetically active radiation (PAR), nutrient status and levels of dissolved CO2, all of which can, in turn, be influenced by global climate change. Thus, increases in CO2 levels can affect the sensitivity of some species to UV-B radiation (UV-B), while others show no such impact on UV-B susceptibility. Both nitrogen- and phosphorus-limitation can have direct interactive effects on the susceptibility of algal cells and communities to UVR, though such effects are somewhat variable. Nutrient depletion can also potentially lead to a dominance of smaller celled species, which may be less able to screen out and are thus likely to be more susceptible to UVR-induced damage. The variability of responses to such interactions can lead to alterations in the species composition of algal assemblages.

We report the coupling of a portable Raman spectrometer to an acoustic levitation device to enable environmental monitoring and the potential taxonomic identification of microalgae. Spectra of living cells were recorded at 785 nm using a fiber-optic probe coupled to a portable Raman spectrometer. The spectra exhibit an excellent signal-to-noise ratio and clearly show bands from chlorophyll a and beta-carotene. Spectra of levitated photobleached microalgae clearly show a reduction in chlorophyll a concentration relative to beta-carotene after 10 min of exposure to a quartz halogen lamp. Spectra recorded from levitated nitrogen-limited cells also show a significant reduction in bands associated with chlorophyll a, as compared to nitrogen-replete cells. To investigate the diagnostic capability of the technique, four species of microalgae were analyzed. Good quality spectra of all four species were obtained showing varying ratios of beta-carotene to chlorophyll. The combination of an acoustic levitation device and a portable Raman spectrometer shows potential as a taxonomic and environmental monitoring tool with direct application to field studies in remote environments.

We studied the growth and photosynthetic characteristics of a toxic (CS506) and a nontoxic strain (CS509) of the bloom-forming cyanobacterium Cylindrospermopsis raciborskii grown under identical experimental conditions. When exposed to light-saturating growth conditions (100 μmol photons · m(-2)  · s(-1) ), values for maximal photosynthetic capacity (Pmax ) and maximum quantum yield (Fv /Fm ) indicated that both strains had an equal ability to process captured photons and deliver them to PSII reaction centers. However, CS506 grew faster than CS509. This was consistent with its higher light requirement for saturation of photosynthesis (Ik ). Greater shade tolerance of CS509 was indicated by its higher ability to harvest light (α), lower photosynthetic light compensation point (Ic ), and higher chlorophyll a to biovolume ratio. Strain-specific differences were found in relation to non-photochemical quenching, effective absorption cross-sectional area of PSIIα-centers (σPSIIα), and the antenna connectivity parameter of PSIIα (Jcon PSIIα). These findings highlighted differences in the transfer of excitation from phycobilisome/PSII to PSI, on the dependence on different pigments for light harvesting and on the functioning of the PSII reaction centers between the two strains. The results of this study showed that both performance and composition of the photosynthetic apparatus are different between these strains, though with only two strains examined we cannot attribute the performance of strain 506 to its ability to produce cylindrospermopsins. The emphasis on a strain-specific light adaptation/acclimation is crucial to our understanding of how different light conditions (both quantity and quality) can trigger the occurrence of different C. raciborskii strains and control their competition and/or dominance in natural ecosystems.

Understanding the effects of global climate change on the algae that form the basis of most aquatic food chains is of paramount importance in our ability to make informed decisions about the future of production systems, marine ecosystems, and the global carbon cycle. Despite the Montreal Protocol to restrict the release of harmful chlorofluorocarbons into the atmosphere, ozone levels have not recovered at all latitudes, and in some regions levels of UVB are still rising due to interactions with phenomena related to climate change. However, the effects of UV radiation may be modulated by other environmental changes. In this review, we discuss how factors such as elevated CO 2 and ocean acidification, increasing temperature, and reduced nutrient supply associated with enhanced stratification can interact with UV radiation to affect algal physiological performance and growth. For instance, nutrient limitation enhances UV-induced inhibition due to the reduced capacity of algae to screen out UVB and/or impairment of their capacity to repair damage. Higher temperatures tend to promote repair more than photochemical damage so result in a net reduction of UV inhibition. Elevated CO 2 and ocean acidification has complex interactions with UV radiation, with mixed net outcomes for algal productivity. Differential effects of UVA and UVB have been shown to depend on their irradiance levels; while moderate levels of UVA stimulate growth and photosynthesis of some algae, UVB almost always results in harm to marine primary producers.

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This investigation examines the occurrence of carbon concentrating mechanisms (CCMs) in eight species of the acellular green marine macroalgal genus Caulerpa. The measurements made were of the ␦ 13 C of organic matter, extracellular carbonic anhydrase activities, pH compensation values, and the inorganic C dependence of light-saturated photosynthesis rates. The data suggest that the pyrenoid-containing C. cactoides and C. geminata, and probably C. scalpelliformis (which lacks pyrenoids) have CCMs. Net diffusive influx of CO 2 fulfills the inorganic carbon requirements of the other species for which pH-drift data are available, i.e. C. flexilis, C. longifolia, C. obscura and C. brownii. No pH drift data are available for C. trifaria and no information is available as to whether it has pyrenoids, although ␦ 13 C data suggest the absence of a CCM in this species. The three species showing evidence of CCMs have the lowest affinities for inorganic C of the eight species tested. This apparently paradoxical finding has precedence for marine red-macroalgae, and requires that the selective significance of the CCMs in these organisms is not that of increased inorganic C affinity, but is perhaps associated with the ability to both suppress photoinhibition and to photosynthesize at higher seawater pH values.