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pH include major (phosphorus, silicon, and nitrogen) and minor (boron) elements as
well as trace elements such as iron and zinc (Doney et al. 2009 ). Moreover, the
concentration of chemical species such as phosphate, silicate, and ammonia
decreases with decreasing pH (Fig. 1.2.11 in Zeebe and Wolf-Gladrow 2001 ).
Recently, a decline in oceanic nitrification rates is reported as a consequence of
OA (Beman et al. 2011 ). The estimated 3-44% reduction in the next decades can
affect oceanic nitrous oxide production, reducing oxidized nitrogen (NO 2 ,NO 3 )
supplies in the upper layers of the ocean, and fundamentally altering nitrogen
cycling in the ocean (Beman et al. 2011 ). The consequence of nutrient speciation
and their bioavailability to macroalgae is largely unknown; fractional changes may
alter photosynthesis, growth, and nutritional value which could affect the rest of the
food web (see Sect. 19.8.1). Likewise, dissolved organic matter (DOM) which
undergoes hydrolytic reactions in seawater, e.g., organic acids, amino acids, nucleic
acids, proteins, and humic materials, will also be effectively altered by changing pH
(Doney et al. 2009 ). Therefore, the overall impact of decreasing pH on these
biologically important organic compounds requires further in-depth investigation.
19.8 Trophic Dynamics and Coastal Ecosystem Response
19.8.1 Stoichiometric Ratio of Aquatic Ecosystems
Interactions between global climate stressors (e.g., CO 2 and temperature) and local
perturbation (e.g., eutrophication) will not only cause regime shifts in coastal
ecosystems favoring spatial expansion of ephemeral turfs and persistence beyond
their normal seasonal limits (Russell and Connell 2009 ) but also stoichiometry of
aquatic ecosystems.
When the ocean becomes enriched with carbon due to rising levels of atmo-
spheric CO 2 , the associated warming and vertical stratification of water suppresses
nutrient supply from deep water into the surface layers. The consequent increase in
carbon and decrease in nutrient concentration results in an increase in the cellular
carbon:nutrient ratio. Phytoplankton with high carbon-to-nutrient ratios are of low
nutritional value for zooplankton; such change in stoichiometry may cascade
throughout the entire aquatic food web (van de Waal et al. 2010 ).
Conversely, if a coastal ecosystem receives a concurrent high supply of nutrients
of anthropogenic sources, the probable consequence of altering the carbon:nutrient
ratios of seaweeds, and their nutritional values to herbivorous fishes and
invertebrates, is largely underappreciated. For example, the molar C:N ratio of
Ulva rigida under nitrogen-limited conditions increased by ~10% when the CO 2
concentration was increased from 350 to 10,000 ppm. However, when the elevated
CO 2 condition was coupled with a 20
20% decrease in
C:N ratio was observed (Gordillo et al. 2001 ). On the other hand, significant
increases in the C:N ratio in a marine angiosperm, Thalassia hemprichii , is reported
under increasing CO 2 ; the increase in tissue carbon content was seen as a positive
increase in nitrogen, a
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