Ecosystem-based approach
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.