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

Abstract

We measured monthly dissolved oxygen (DO) changes in situ benthic incubations from March 2001 to October 2002 in a Posidonia oceanica meadow and unvegetated sediments of Magalluf Bay (Mallorca Island, Spain) to determine gross primary production (GPP), community respiration (R), and net community production (NCP). From June 2001 to October 2002, we also measured fluxes of dissolved inorganic carbon (DIC) and total alkalinity (TAlk). The yearly integrated metabolic rates based on DO changes show that the P. oceanica communities are net autotrophic while the metabolic rates in the unvegetated benthic communities are nearly balanced. Higher calcium carbonate (CaCO 3 ) cycling, both in terms of production and dissolution, was observed in P. oceanica communities than in unvegetated benthic communities. In the P. oceanica meadow, the annual release of CO 2 from net CaCO 3 production corresponds to almost half of the CO 2 uptake by NCP based on DIC incubations. In unvegetated benthic communities, the annual uptake of CO 2 from net CaCO 3 dissolution almost fully compensates the CO 2 release by NCP based on DIC incubations. CaCO 3 dynamics is potentially a major factor in CO 2 benthic fluxes in seagrass and carbonate-rich temperate coastal ecosystems.

Photosynthesis, respiration and calcification in the Mediterranean crustose coralline algaLithophyllum cabiochae(Corallinales, Rhodophyta)

“…Despite its moderate diel net community carbonate production relative to shallower systems, the coralligenous community can be considered as a major contributor to calcium carbonate deposition in the Mediterranean Sea. For comparison, diel carbonate production is several times higher than that of NW Mediterranean infralittoral communities dominated by the articulated coralline alga, Corallina elongata (8 mmol CaCO 3 m −2 d −1 : Bensoussan & Gattuso, 2007) and that of Posidonia oceanica meadows (1.5 mmol CaCO 3 m −2 d −1 : Barrón et al, 2006). This study confirms that coralline algae and coralligenous habitat are major contributors to biogenic carbonate production in the NW Mediterranean Sea (Canals & Ballesteros, 1997) and that they may significantly influence regional carbon and carbonate budgets.…”

Spatial and temporal CO<sub>2</sub> exchanges measured by Eddy Covariance over a temperate intertidal flat and their relationships to net ecosystem production

“…First, microphytobenthic cells can migrate down to deeper layers of the sediment at night as protection against grazing by depositfeeders (Blanchard et al, 2001); thus, respiration would not release CO 2 to the atmosphere but deeper into the sediments. Second, CO 2 generated by benthic respiration could be almost entirely involved in the dissolution of carbonate shells and not released to the atmosphere, as occurred for instance in a Mediterranean seagrass meadow (Posidonia oceanica) in winter (Barrón et al, 2006). The Arcachon flat represents an important stock of carbonates of about 120 Mt of several shellfish species as Crassostrea gigas contributing to 95 % (D. M. X.…”

Influence of giant kelp beds (Macrocystis pyrifera) on diel cycles of pCO2 and DIC in the Sub-Antarctic coastal area

“…In the Bay of Palma (Spain), strong decreases in pCO 2 over Posidonia meadows have been reported due to the meadows' higher primary productivity compared to the surrounding oligotrophic waters (Gazeau et al, 2005). In the same area, Barrón et al (2006) highlighted the strong influence of calcification by epiphythes and calcium carbonate (CaCO 3 ) dissolution on CO 2 dynamics in Posidonia meadows, which is in agreement with observations of other seagrass ecosystems (Morse et al, 1987;Ku et al, 1999;Delille et al, 2000;Burdige and Zimmerman, 2002;Yates and Halley, 2003;Yates and Halley, 2006). On the whole, Posidonia oceanica seagrass meadows appear to act as a sink for atmospheric CO 2 .…”