| Summary: | Over the past decade there has been rapidly growing interest in the potential effects of ocean acidification and perturbations of the carbonate system on marine organisms. While early studies focused on a handful of phytoplankton and calcifying invertebrates, an increasing number of investigators have begun to examine the sensitivity to ocean acidification of various planktonic and benthic organisms across the marine food web. Several excellent review articles have recently summarized the rapidly expanding literature on this topic (Fabry et al. 2008; Doney et al. 2009 Joint et al. 2011). The focus of this chapter is on the potential ecosystem-level effects of ocean acidification. Starting with a brief review of the basic physical, chemical, and biological processes which structure pelagic marine ecosystems, the chapter explores how organismal responses to perturbations of the carbonate system could scale up in both time and space to affect ecosystem functions and biogeochemical processes. As with many chapters in this volume, and indeed much of the ocean acidification literature at present, our review raises more questions than it answers. It is hoped that these questions will prove useful for articulating and addressing key areas of future research. Complexity in marine pelagic food webs results from the interactions of multiple trophic levels across a range of temporal and spatial scales. The traditional view of marine food webs (Steele 1974) involved a relatively short trophic system in which large phytoplankton (e.g. net plankton such as diatoms) were grazed by a variety of mesozooplankton (e.g. copepods), which were in turn consumed by second-level predators, including many economically important fish and invertebrate species. This ‘classic’ marine food web is typical of high-productivity regions such as coastal upwelling regimes (Lassiter et al. 2006). A characteristic feature of these systems is a strong decoupling between primary production and grazing, which results from the different metabolic rates ...
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