THE FATE OF MARINE AUTOTROPHIC PRODUCTION

The fate of photosynthetic carbon in marine ecosystems dominated by di fferent types of primary producers was examined by compiling published reports on herbivory, autotrophic respiration, decomposition, carbon storage, and export rates as fractions of net primary production (NPP) in ecosystems dominated by different types of autotrophs (i.e. oceani c and coastal phytoplankton, microphytobenthos, coral reef algae, macr oalgae, seagrasses, marsh plants, and mangroves). A large fraction (>4 0%) of the NPP of marine ecosystems is decomposed within the system, e xcept for microphytobenthos (decomposition, similar to 25% of NPP). He rbivory tends to be highest for microalgae (planktonic and benthic, >4 0% of NPP) and macroalgae (33.6+/-4.9% of NPP) and is somewhat less fo r higher plants. Microphytobenthos export on average a much higher pro portion of their NPP than do other microalgal communities, whereas mar ine macrophytes, except marsh plants, export a substantial proportion (24.3-43.5% on average) of their NPP. The fraction of NPP stored in se diments is 4-fold greater for higher plants (similar to 10-17% of NPP) than for algae (0.4-6% of NPP). On average, similar to 90% of the phy toplankton NPP is used to support local heterotrophic metabolism (i.e. grazed or decomposed). This fraction is even higher in oceanic commun ities. Mangrove forests, and to a lesser extent seagrass meadows and m acroalgal beds, produce organic carbon well in excess of the ecosystem requirements, with excess photosynthetic carbon (i.e. export rate plu s storage) in these ecosystems representing similar to 40% of NPP. Ext rapolation of these results to the global ocean identifies marine angi osperms, which only contribute 4% of total ocean NPP, as major contrib utors of the NPP stored (30% of total ocean carbon storage) and subseq uently buried in marine sediments. Consideration of burial of NPP from marine angiosperms should lead to estimates of total burial of marine NPP that exceed current estimates by 15-50%.