Modelling CO2 budget of mussel farms across the Mediterranean Sea

Abstract

The role of bivalve aquaculture as a carbon sink is highly debated, without a general consensus on the components to include in the budget. This study proposes to estimate the terms of the budget using a scope-for-growth-based model. The model was applied at 12 Mediterranean sites, with environmental forcings provided by operational oceanography data spanning over 12 years. Mussels were found to be slight sinks, with a limited variability across sites, if all components of the budget, i.e. accumulation in soft tissue, emissions associated with calcification and respiration, are included. The differences found among stations concerning the calcification and soft tissue contributions to the budget were found to be related to site-specific productivity and water chemistry parameters. This led to the identification of a set of meta-models, which could be used for relating the budget to local conditions, at a screening level, rendering them useful for optimal site selection.

Keywords: Bivalves; Carbon fluxes; Mytilus galloprovincialis; Restorative aquaculture; Satellite data; Scope for growth.

Fig. 1

Location of the 12 representative sites considered within this work. Coordinates of each site are provided in Table S1 (Online Resource 1 S1)

Fig. 2

Model simulations (grey lines) for dry soft (top) and shell (bottom) tissue dry weights (in grams), compared to means (black dots) and standard deviations (error bars) sampled from the Venice lagoon

Fig. 3

Boxplots of median annual values from 2007 to 2019 of environmental model forcings (Chlorophyll-a, POC, temperature, total alkalinity, pH) at each of the 12 stations

Fig. 4

Growth curves of total dry weight (somatic tissue, gonads and shell) at each of the 12 stations. Full line represents mean and dotted lines represent standard deviations

Fig. 5

Boxplots of annual CO₂ fluxes at the 12 study sites (positive values refer to emissions, negative to removal). A total budget (calculated as described in Eq. 4), B amount stored in the soft tissue, C amount emitted through calcification, D amount emitted through respiration. All fluxes are reported as g CO_2eq ind⁻¹ year⁻¹. Box edges indicate the 1st and 3rd quartiles, the central line marks the median, while whiskers indicate extreme (max–min) data points not considered outliers (plotted individually using the “°” symbol)

Fig. 6

CO_2eq budgets calculated following Eqs. 2–4 (empty dots: CO₂ total; full black dots: CO₂ soft tissues net; full grey dots: CO₂ shell net), plotted against environmental forcings (from top to bottom: Chlorophyll-a, water temperature, POC, pH, total alkalinity)