| Summary: | The vast majority of the seafloor is covered not in rocky or biogenic reefs but in unconsolidated sediments and, consequently, the majority of marine biodiversity consists of invertebrates either residing in (infauna) or on (epifauna) sediments (Snelgrove 1999). The biodiversity within these sediments is a result of complex interactions between the underlying environmental conditions (e.g. depth, temperature, organic supply, and granulometry) and the biological interactions operating between organisms (e.g. predation and competition). Not only are sediments important depositories of biodiversity but they are also critical components in many key ecosystem functions. Nowhere is this more apparent than in shallow coastal seas and oceans which, despite covering less than 10% of the earth’s surface, deliver up to 30% of marine production and 90% of marine fisheries (Gattuso et al. 1998). These areas are also the site for 80% of organic matter burial and 90% of sedimentary mineralization and nutrient–sediment biogeochemical processes. They also act as the sink for up to 90% of the suspended load in the world’s rivers and the many associated contaminants this material contains (Gattuso et al. 1998). Human beings depend heavily on the goods and services provided, for free, by the marine realm (Hassan et al. 2005 ) and it is no coincidence that nearly 70% of all humans live within 60 km of the sea or that 75% of all cities with more than 10 million inhabitants are in the coastal zone (Small and Nicholls 2003; McGranahan et al. 2007) Given these facts, it is clear that any broad-scale environmental impact that affects the diversity, structure, and function of sediment ecosystems could have a considerable impact on human health and well-being. It is therefore essential that the impacts of ocean acidification on sediment fauna, and the ecosystem functions they support, are adequately considered. This chapter will first describe the geochemical environment within which sediment organisms live. It will then explore the role ...
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