Abstract

The role of marine bivalves in the CO2 cycle has been commonly evaluated as the balance between respiration, shell calcium carbonate sequestration, and CO2 release during biogenic calcification; however, this individual-based approach neglects important ecosystem interactions that occur at the population level, e.g. the interaction with phytoplankton populations and benthic-pelagic coupling, which in turn can significantly alter the CO2 cycle. Therefore, an ecosystem approach that accounts for the trophic interactions of bivalves, including the role of dissolved and particulate organic and inorganic carbon cycling, is needed to provide a rigorous assessment of the role of bivalves as a potential sink of CO2. Conversely, the discussion about this potential role needs to be framed in the context of non-harvested vs. harvested populations, given that harvesting represents a net extraction of matter from the ocean. Accordingly, this chapter describes the main processes that affect CO2 cycling and discuss the role of non-harvested and harvested bivalves in the context of sequestering carbon. A budget for deep-fjord waters is presented as a case study.

Highlights

  • Bivalves are soft-bodied organisms protected by an external shell consisting of two hinged valves

  • The sequestration of CO2 in the shell is not enough to compensate the release generated during the respiration of organic matter

  • Note that the use of the term “production” was avoided within the manuscript in the context of bivalves “producing” CO2. This has been done intentionally to avoid negative connotations associated with being a CO2 generator

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Summary

12.1 Introduction

Bivalves are soft-bodied organisms protected by an external shell consisting of two hinged valves. Cultured bivalves can exert a bottom-up nutrient control in stimulating primary production (Cranford et al 2007; Jansen 2012), this positive effect is density dependent, with a resulting high bivalve biomass causing a reduction in primary production (Burkholder and Shumway 2011; Smaal et al 2013). Given their ideal growing conditions, growth rates of cultured populations are usually higher than for wild populations; the most critical aspect of cultured bivalves is that their biomass is extracted from the ocean, a relevant consideration when comparing the role of wild versus cultured populations in biogeochemical cycles.

12.2 The Role of Calcifying Organisms in the CO2 Budget
12.3 The Influence of Organic Carbon on CO2 Fluxes
12.4 Ecosystem Services of Non–Harvested and Harvested Populations
12.5 Case-Study
12.5.1 Respiration
12.5.2 The Shell
12.5.3 The Tissue
12.5.4 Egestion of Unabsorbed Food
12.5.5 General Budget in the Context of Ecosystem Services
Findings
12.6 Conclusions
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