Decomposition Of Marine Primary Producers: Consequences For Nutrient Recycling And Retention In Coastal Ecosystems

Coastal marine plant communities are, in contrast to the open sea where the only primary producers are phytoplankton, made up by a number of different plant groups that each contribute to total autotrophic biomass and production (Borum & Sand- Jensen, 1996); Hauxwell and Valiela, Chapter 3). Coastal plant communities rank among the most productive biomes on earth and large amounts of nutrients (especially N and P) pass therefore through this compartment (Pedersen et al., chapter 1). Nutrients assimilated during plant growth are immobilized temporarily in living biomass and detritus until they are mineralized through grazing or decomposition. Incomplete or very slow decomposition of detrital components that are resistant to decomposition may, however, lead to long term or permanent (i.e. over decades, centuries) storage of organic matter and associated nutrients. Whether detritus-bound nutrients are mineralized and recycled quickly or whether they become stored in slowly degradable detritus over longer time scales is controlled by the rates and patterns of the decomposition of plant detritus. The percentage of net primary production that is lost through grazing versus decomposition differs among major groups of marine primary producers (i.e. phytoplankton, macroalgae and seagrasses) (Cebrián, 1999; Duarte, 1995; Duarte & Cebrián, 1996).