Abstract
Abstract. The ongoing increase in anthropogenic carbon dioxide (CO2) emissions is changing the global marine environment and is causing warming and acidification of the oceans. Reduction of CO2 to a sustainable level is required to avoid further marine change. Many studies investigate the potential of marine carbon sinks (e.g. seagrass) to mitigate anthropogenic emissions, however, information on storage by coralline algae and the beds they create is scant. Calcifying photosynthetic organisms, including coralline algae, can act as a CO2 sink via photosynthesis and CaCO3 dissolution and act as a CO2 source during respiration and CaCO3 production on short-term timescales. Long-term carbon storage potential might come from the accumulation of coralline algae deposits over geological timescales. Here, the carbon storage potential of coralline algae is assessed using meta-analysis of their global organic and inorganic carbon production and the processes involved in this metabolism. Net organic and inorganic production were estimated at 330 g C m−2 yr−1 and 900 g CaCO3 m−2 yr−1 respectively giving global organic/inorganic C production of 0.7/1.8 × 109 t C yr−1. Calcium carbonate production by free-living/crustose coralline algae (CCA) corresponded to a sediment accretion of 70/450 mm kyr−1. Using this potential carbon storage for coralline algae, the global production of free-living algae/CCA was 0.4/1.2 × 109 t C yr−1 suggesting a total potential carbon sink of 1.6 × 109 tonnes per year. Coralline algae therefore have production rates similar to mangroves, salt marshes and seagrasses representing an as yet unquantified but significant carbon store, however, further empirical investigations are needed to determine the dynamics and stability of that store.
Highlights
Concentrations of atmospheric CO2 simulated by coupled climate-carbon cycle models range between 730 and 1200 ppm by 2100 (Meehl et al, 2007)
While crustose coralline algae (CCA) grow exclusively on hard surfaces, free-living coralline algae are able to form rhodoliths when they settle on non-cohesive particulate substrates or are detached from existing hard substrates by fragmentation (Bosence, 1983)
Figueiredo et al (2008) indicate that the surface covered by CCA on the Abrolhos Bank (20 900 km2) in Brazil ranges from 5–40 % on the reef flats, 30–80 % on the reef crests and 10–50 % on the reef walls with coverage varying due to differences in the abundance of turf algae and herbivory pressure
Summary
An increase in exploitation of fossil fuels since the mid-18th century caused a rise in the partial pressure of carbon dioxide in both atmospheric (CO2) and oceanic (pCO2) reservoirs (Sabine et al, 2004; Meehl et al, 2007). A. Kamenos: Calculating the global contribution of coralline algae capacity (Duarte et al, 2005) and the potential of marine coastal vegetation as a sink for anthropogenic carbon emissions (blue carbon) is becoming of interest (Nellemann et al, 2009). Coralline algae are important contributors to the marine calcium carbonate (CaCO3) deposited in the coral reef sediments (Goreau, 1963; Adey and Macintyre, 1973) and account for approximately 25 % of CaCO3 accumulation within coastal regions (Martin et al, 2007). Calcifying photosynthesisers are both a sink and a source of CO2 (Frankignoulle, 1994). We aim to estimate the global distribution of coralline algae, and from that, determine their potential role in long-term total carbon burial
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