Read what Canada has found to be true or at least, likely, of ocean acidification's effects on the Scotian Shelf ecosystem in the State of the Scotian Shelf 2012, We observe that like theirs, our region's marine microbes that create tiny calcium based shells to live within are affected by reduced pH - as much as or more than we megafauna and macrophytes! Here's the report's section on marine microbes
4.3 Calcifying Micro-
organism Productivity Micro-organisms are small bacteria, phytoplankton, zooplankton, and invertebrate species. They are responsible for almost half of all global primary productivity (Rost et al. 2008). Primary productivity is the production of oxygen and other organic compounds.
Micro-organisms are also the basis of the marine food web. Due to climate change, changes in dissolved carbon dioxide concentrations, pH, dissolved oxygen, temperature, and stratification will all combine to influence the composition and dominance of micro-organisms in the sea. This will impact their role in respiration, nutrient cycling, and many other important biological processes (Rost et al. 2008) (see Climate Change theme paper).
In some instances, however, increased dissolved carbon dioxide in ocean waters could exhibit beneficial impacts on certain micro-organism species, due to varying respiratory responses. For others, more negative responses may be observed.
In short, increased carbon dioxide dissolution in the sea is expected to affect micro-organism species differently, by impacting species-specific productivity, composition, assemblage, and succession (Orr et al. 2005; Rost et al. 2008).
Calcification is important to the prosperity of many micro-organisms by way of body structure, functioning, and protection (Pörtner 2008). Calcification is often a function of complex physiological processes in organisms that make use of bicarbonate or trapped carbon dioxide rather than carbonate, thus, although carbonate saturation may be a good proxy for calcification it is not necessarily a direct driver at the organism level (Atkinson and Cuet 2008; Pörtner 2008).
Some calcareous-based micro-organisms can survive extended periods of time in the absence of their calcareous structures, while many oth
ers cannot (e.g., echinoderms such as starfish) (Pörtner 2008). Typical calcareous marine micro-organisms include foraminifera (calcite shells), coccolithophores (calcite shells), and euthecosomatous pteropods (aragonite shells). They account for almost all of the flux of calcium carbonate from the ocean’s surface waters to the deep sea (Fabry et al. 2008). Foraminifera and euthecosomatous pteropods are particularly important inhabitants of sub-polar regions such as the Scotian Shelf. Micro-organisms vary in their response to ocean acidification, even within like species, and this has implications for the adaptation of individual species (Fabry et al. 2008). For lower trophic calcifying marine micro-organisms, such as Emiliania huxleyi (Figure 7), declines in their population may have significant implications on the ecosystem as a whole, by causing changes in food chain dynamics (Riebesell et al. 2000; Fabry et al. 2008; Rost et al. 2008). Emiliania huxleyi are commonly found in the waters of Atlantic Canada, includi-
ng those on the eastern Scotian Shelf (Brown and Yoder 1994). The species is particularly vulnerable to changes in ocean pH. In general, acute and long-term sensitivity to dissolved carbon dioxide is likely to be highest in lower trophic invertebrate species, which are poorlysuited to tolerate changes that can influence important life processes such as calcification (Pörtner 2008). The result is a lower tolerance of these species to changes in temperature that will reduce their spatial distribution, associated species interactions, and affect their role in the ecosystem (Pörtner 2008). Pteropods are particularly vulnerable to ocean acidification due to their highly-soluble aragonite shells, while very little is known about the impacts of ocean acidification on cnidarians, sponges, bryozoans, annelids, brachiopods, and tunicates (Fabry et al. 2008). In contrast, increased dissolved carbon dioxide appears to have little impact on marine diatoms (Fabry et al. 2008). Some zooplankton species may exhibit diminished respiration, with species reliant on calcium carbonate showing signs of depressed physiological function (Royal Society 2005; Fabry et al. 2008; Rost et al. 2008)
FIGURE 7. Evidence of reduced calcification in two calcareous marine coccolithophore plankton species: Emiliania huxleyi (see Panels a,b, d, and e) and Gephyrocapsa oceanica (see Panels c and f) (Riebesell et al. 2000). The organisms were exposed to simulated dissolved carbon dioxide concentrations of approximately 300 ppm by volume (Panels a–c) and 780-850 ppm by volume (Panels d–f), respectively. The scale bar represents 1 micrometre (µm) in length (one thousandth of a millimetre). At the higher simulated dissolved carbon dioxide concentrations, organisms demonstrated signs of malformation, as represented by abnormalities in their shape and roughness of their edges (reprinted with permission from the Nature Publishing Group, Macmillan Publishers Ltd: Nature, Riebesell et al. 2000)..
Elevated dissolved carbon dioxide concentrations favour plankton species with high carbon demands and low surface area-tovolume ratios, that is, larger micro-organism species or species that lack carbon dependence. As a result, increased dissolved carbon dioxide may cause a shift in the global ocean’s planktonic community structure (Wolf-Gladrow et al. 1999). For instance, non-photosynthetic micro-organisms such as bacteria, fungi, and protists may prosper under conditions of a lowered-pH sea. Many of these organisms have greater metabolic variability, which could give them a competitive advantage (e.g., nitrogenfixing cyanobacteria may benefit from ocean acidification) (Royal Society 2005). This could further contribute to an altered chem
stry of the sea (Orr et al. 2005). Last, increased dissolved carbon dioxide in the sea may increase the extra-cellular polysaccharides found on surfaces of plankton organisms. Extra-cellular polysaccharides behave as a glue that binds multiple organisms into large aggregates, subsequently altering the residence time and flux of planktonic biomass from surface waters into the deep sea (Royal Society 2005). As a result, essential minerals and energy found in the surface ocean could also dramatically change
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