Picocystis data by courtesy of james hollibaugh

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Picocystis . Data by courtesy of James Hollibaugh, University of Georgia at Athens. OGU11 8/14/04 11:52 AM Page 234
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Global environmental issues CHAPTER 11 235 Picocystis species, strain ML, accounts for approximately 25% of the primary production during the winter bloom, and its contribution exceeds 50% during other seasons (Roesler et al ., 2002). Therefore, environmental factors, which are not conducive to the growth of this organism will be reflected in the observation of a decline in primary production, and in all other biogeochemical processes depending on primary productivity. As such, Picocys- tis is a good indicator organism for ecosystem function in this seemingly low-diversity envi- ronment. However, the robustness of biological indicators is subject to strong biotic influences, and indeed Humayoun and colleagues (2003) demonstrated a complex bacterial diversity in the proximity of the habitat colonized by Picocystis . By employing protocols based on direct DNA analysis to reveal the presence of phylogenetic groups, these investi- gators showed that samples collected from the oxycline zone had low bacterial diversity with only nine phylotypes, whereas the chemocline contained 27 phylotypes. These bacteria belong to the five major lineages of the domain Bacteria, namely alpha- and gamma- Proteobacteria ; Cytophaga-Flexibacter- Bacteroides ; Actinobacteria ; Bacillus ; and Clostridium . It is not yet clear from these findings what is the nature of the interactions that occur between the dominant primary producer, Picocystis , and the diverse heterotrophic bacteria with which it co-exists. There are strong prospects that additional broad-spectrum indicators of extreme environmental change will be recovered from ecosystems typified by Mono Lake. STRATOSPHERIC OZONE DEPLETION As in the case of humans, microbial activities contribute ozone-depleting chemicals to the atmosphere, and they are also sensitive to the impacts of stratospheric ozone depletion through increased exposure to ultraviolet radiation. A sophisticated real-time information database is available for monitoring the size of the ozone layer in the stratosphere, and there is a well-developed index of specific health risks to human populations in many part of the world (Fig. 11.4) (de Gruijl et al ., 1994; Setlow et al ., 1993). In contrast, indexes of ecologi- cal impacts of increased UV exposure are either non-existent or poorly developed. This lack of information is due in part to the very wide range of exposure and responses exhibited by wildlife organisms and ecosystem processes to increased UV exposures (Blumthaler and Ambach, 1990; Fleischmann, 1989). In addition, ecological effects of UV exposure are likely to cascade hierarchically, rather than to remain with affected individuals or processes (Herndl et al ., 1993; Lyons et al ., 1998). Therefore, attempts to produce generalized response models that could serve as the foundation for the development of reliable indicators are fraught with uncertainties.
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