Respiration in coastal benthic communities

Abstract

This chapter reviews coastal benthic communities with the aim of deriving a global estimate for respiration in these ecosystems. Reefs, mangroves, salt marshes, macroalgae, sea grasses, and unvegetated sediments dominate respiration in the coastal ocean. Estimates of coastal benthic respiration are not well constrained but converge on about 620 Tmol C a −1. In coastal benthic ecosystems autotrophs and multicellular heterotrophs contribute significantly, and in some systems even dominate respiration unlike most other oceanic ecosystems in which bacteria dominate respiration.

Major role of marine vegetation on the oceanic carbon cycle

“…We first estimate carbon burial in vegetated habitats following two approaches, a bottom-up approach derived from upscaling individual estimates of carbon burial in vegetated habitats to the global level, and a top-down approach derived from considerations of the global sediment balance (Berner, 1982). We then construct a carbon budget for the coastal ocean, including carbon burial, respiration (from Middelburg et al, 2005), and gross primary production (from Duarte and Cebrián, 1996), and examine, using mass balance considerations, the possible organic export from vegetated habitats to the open ocean and the impact of destruction of marginal coastal habitats where marine vegetation dominates on the carbon budget of the global ocean.…”

“…However, the possibility of C burial in macroalgal Table 3. The metabolic balance of the benthic coastal communities, as represented by the respiration rates (R, average and global values from Middelburg et al, 2005), gross primary production (GPP), computed using average values from net primary production and autotrophic respiration estimates in Duarte and Cebrián (1996) and GPP estimates in Gattuso et al (1998) for coral reefs, upscaled to the global coastal ocean using the surface areas covered by the communities reported in Table 1, and Duarte and Cebrián (1996) for macroalgae and microphytobenthos; and the net ecosystem production (NEP=GPP-R) for these ecosystems. beds has not been studied and, therefore, cannot be included in this assessment.…”

“…Estimates of respiration (R) in vegetated habitats have been recently compiled using a dual top-down and bottom-up approach as done here (Middelburg et al, 2005). The resulting estimate of R in vegetated habitats was 5310 Tg C y −1 , with a particularly high contribution by macroalgae (Table 3).…”

Organic carbon metabolism and carbonate dynamics in a Mediterranean seagrass (Posidonia oceanica), meadow

“…The interference of seagrass canopies with water flow leads to enhanced particle deposition, retention, and degradation (Agawin and Duarte 2002;Gacia et al 2002;Duarte et al 2004). The high production and input of organic carbon make seagrass meadows sites of elevated microbial activity, as well as enhanced animal abundance, which result in high heterotrophic activity (Hemminga and Duarte 2000;Middelburg et al 2005). In addition to their important metabolic activity, seagrass meadows also support high calcium carbonate (CaCO 3 ) production (cf., Canals and Ballesteros 1997;Gattuso et al 1998;Gacia et al 2003) and dissolution (Morse et al 1987;Ku et al 1999;Burdige and Zimmerman 2002).…”

“…These fluxes are seldom examined in concert so that carbon budget of seagrass meadows, and their potential role as carbon sinks or sources, remains poorly constrained. There is an abundant literature on the organic carbon metabolism of seagrasses (Gattuso et al 1998;Hemminga and Duarte 2000;Middelburg et al 2005). Most studies focused on dissolved oxygen (DO) changes, but this is only a good indicator in the presence of anaerobic respiration when the reduced products are oxidized (Canfield et al 1993).…”