For growth, phytoplankton cells depend on nutrients, which enter the ocean by rivers, continental weathering, and glacial ice meltwater on the poles. Changes in the vertical stratification of the water column, the rate of temperature-dependent biological reactions, and the atmospheric supply of nutrients are expected to have important effects on future phytoplankton productivity. Phytoplankton are photosynthesizing microscopic biotic organisms that inhabit the upper sunlit layer of almost all oceans and bodies of fresh water on Earth. Ocean acidification may affect coastal ecosystems in a variety of ways. Phytoplankton form the base of marine and freshwater food webs and are key players in the global carbon cycle. The photosynthetically fixed carbon is rapidly recycled and reused in the surface ocean, while a certain fraction of this biomass is exported as sinking particles to the deep ocean, where it is subject to ongoing transformation processes, e.g., remineralization. Recent progress has been made toward attributing ecological shifts, particularly in terrestrial systems, to climate change (Rosenzweig et al., 2008). While many studies indicate that calcification correlates with the calcium carbonate saturation state of seawater, biological thresholds of the calcification response to ocean acidity may be species-specific. In many regime shifts, once an ecological threshold has been passed, the driver of the change must be reversed to levels far beyond where the shift occurred before the system shifts back to its original state. In some cases, an increase in non-calcifying primary producers on reefs (seagrasses and macroalgae) may counter the effects of ocean acidification, by drawing down CO2 directly from the water column during photosynthesis (Palacios and Zimmerman, 2007; Semesi et al., 2009a). It is presently unknown to what extent these responses affect the competitive abilities, susceptibility to viral attack, predator-prey interactions, or the fitness of calcifying plankton. Phytoplankton. The primary reef-building species are stony corals that lack zooxanthellae, the symbiotic algae common in shallow, tropical species. It is probable that an increase in total seagrass area will lead to more favorable habitat and conditions for associated invertebrate and fish species (Guinotte and Fabry, 2009). These events, also accompanied by low pH, may indicate that most coastal ecosystems are sensitive to extreme eutrophication events. Calcification rates in the cold-water species Lophelia pertusa were reduced by an average of 30 and 56% when pH was lowered by 0.15 and 0.3 units relative to ambient conditions, respectively (Maier et al., 2009), but despite this response, calcification rates in this species did not stop completely even in aragonite-undersaturated conditions. The most obvious and best documented effect of ocean acidification is the depression of calcification rates, which will affect skeletal growth of the reef-building organisms. In oligotrophic oceanic regions such as the Sargasso Sea or the South Pacific Gyre, phytoplankton is dominated by the small sized cells, called picoplankton and nanoplankton (also referred to as picoflagellates and nanoflagellates), mostly composed of cyanobacteria (Prochlorococcus, Synechococcus) and picoeucaryotes such as Micromonas. The air we breathe would be toxic if it weren’t for plant photosynthesis of which oxygen is a by-product. Reduced growth and calcification rates, and in. In coral reefs, for example, whether the loss of corals is due to rising temperature or from ocean acidification may have little relevance in the overall impact on the ecosystem (loss of corals impacts the base function of the ecosystem). These include expected effects on phytoplankton, which serve as the base of marine food webs, and on ecosystem engineers, which create or modify habitat (e.g., corals, oysters, and seagrasses). In addition, the exchange of carbon dioxide and other climatically relevant trace gas species with the atmosphere may be modified, thus inducing feedbacks on the climate system. There was not a comparable extinction in shallow-water species such as mollusks, but the occurrence of weakly calcified planktonic foraminifera may indicate changes in carbonate ion concentration in surface waters. Although there are major differences in the modern biota and structure of benthic communities in the Arctic and Southern Ocean that reflect the distinct topography and evolutionary history of the polar habitats, there may be similar vulnerabilities in the two systems. A unique habitat type in the deep sea that deserves particular attention is cold-water coral communities. [11], Phytoplankton depend on B Vitamins for survival. Behrenfeld, M.J. and Boss, E.S. MyNAP members SAVE 10% off online. During photosynthesis, they assimilate carbon dioxide and release oxygen. While many of these hypothesized effects seem logical, most have not yet been explicitly tested. In mariculture, the phytoplankton is naturally occurring and is introduced into enclosures with the normal circulation of seawater. As in the PETM, calcifying organisms suffered greater extinction rates than organisms that do not produce CaCO3, but the ecological responses that can be reconstructed could have been the result of the collapse of photosynthesis from the darkened skies, or disruption of other geochemical factors, in addition to or instead of changes in ocean pH. Phytoplankton is a microscopic plant, a component of the plankton, which spends its life being carried by oceanic currents. Interestingly, Miller et al. FIGURE 4.3 Global dataset of more than 30,000 potential seamounts (Kitchingman and Lai, 2004; www.seaaroundus.org). The ocean does not take up carbon uniformly. Several laboratory studies indicate that reef-building crustose coralline algae will calcify more slowly (e.g., 50% reduction; Reynaud et al., 2003; Anthony et al., 2008). [39][44][45] Conversely, rising CO2 levels can increase phytoplankton primary production, but only when nutrients are not limiting. The actual increase in nitrogen fixation, however, could be limited by phosphorus or iron supplies. But in regions that are only hypoxic, the low oxygen and the high CO2 tend to act in concert to make respiration difficult for a number of aerobic organisms. While it is important to understand how ocean acidification will change ocean chemistry and the physiology of marine organisms, as reviewed in chapters 2 and 3, what is equally critical is to understand how these effects may scale up to populations, communities, and entire marine ecosystems. The environmental stability of the deep sea over long time scales is also postulated to have reduced the tolerance of deep-sea species to environmental extremes through the loss of more tolerant genotypes (Dahlhoff, 2004), thereby decreasing the potential for adaptation to future ocean acidification. Decreased coral calcification rates are evident on the Great Barrier Reef, where records from massive corals show that calcification rates decreased by about 14% between 1990 and 2005 (De’ath et al., 2009), although the relative roles of increased temperature and ocean acidification could not be determined. Under future conditions of anthropogenic warming and ocean acidification, changes in phytoplankton mortality due to changes in rates of zooplankton grazing may be significant. A 2018 study estimated the nutritional value of natural phytoplankton in terms of carbohydrate, protein and lipid across the world ocean using ocean-colour data from satellites,[37] and found the calorific value of phytoplankton to vary considerably across different oceanic regions and between different time of the year.
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