Compilation of metabolic data indicates that the ratio gross primary production versus respiration (GPP:R) exhibit a large variability and are in most cases not statistically different from 1. The open shelf, the various macrophyte systems, and coral reefs are typically net autotrophs as shown by GPP:R > 1 and net ecosystem production (NEP) > 0). Many estuaries exhibit a negative net ecosystem production (-10 Tmol C yr-1) and are net heterotrophs. There remains a debate as to whether the coastal ocean taken as a whole is net autotrophic or heterotrophic. Up-scaling the system-level data to the whole coastal zone, provides a GPP value of 789 Tmol C yr-1; or 23% of the global marine gross primary production. This is of the same order of magnitude as the previous estimate of 500 Tmol C yr-1.
The ecosystem approach provides an NEP estimate of 235 Tmol C yr-1, a value in good agreement with that provided by Wollast (200 Tmol C year-1) but much higher than the figure of -7 Tmol C yr-1 proposed by Smith & Hollibaugh or the value of 12 Tmol C yr-1 given by Rabouille. The continental shelf (excluding specific ecosystems) is the major contributor to the NEP of the costal zone (75%) followed by macrophyte-dominated ecosystems (16%), mangroves (7%), marshes (3%) and coral reefs (2.6%).
The contribution of the coastal ocean to marine calcium carbonate production is greater than 40% (23 Tmol CaCO3 yr-1 out of 53 Tmol yr-1). The highest deposition occurs in coral reef habitats (9 Tmol yr-1), followed by banks and embayments (4 Tmol yr-1), carbonate shelves (6 Tmol yr-1) and non-carbonate shelves (4 Tmol year-1).