Particulate matter is derived from decaying and fragmented plant material and 

 algal cellular debris. Zooplankton play an important role in transforming 

 particulate matter, through feeding and release of fecal pellets (larger 

 animals are not considered here due to proportionately smaller input into the 

 system). During conversion of particles, dissolved compounds are produced 

 through extracellular release, protoplasm is released during death or breakage 

 of cells, and feces are excreted by grazing animals. Some simple molecules 

 can be reassimilated by phytoplankton. 



The importance of bacteria in the cycling of organic matter is not fully 

 understood. Bacteria assimilate dissolved compounds and release carbon 

 dioxide and nutrients. Bacteria can attach to particles and living cells and 

 hasten their decomposition by liberating enzymes. These colonized particles 

 are eaten by filter-feeding and deposit-feeding animals. One current view 

 suggests that the majority of organic cycling in the water column is 

 accomplished by unattached bacteria that maintain the concentrations of 

 readily-assimilated compounds (e.g., sugars and amino acids) at very low 

 levels . 



Components of the organic cycle that are unique to Maine are contributed by 

 the pulp and paper industry and other point-source discharges of processed 

 waste (see chapter 3, "Human Impacts on the Ecosystem"). 



A schematic diagram of the organic matter cycle in the marine system is given 

 in figure 4-18. 



DISSOLVED 



ORGANIC 



MATTER 



Q. 



O 



LU 



\ la. 



PARTICULATE 



ORGANIC 



MATTER 



FECAL PELLETS 



p^\0^ 



SINKING 



PHYTOPLANKTON 

 AND ATTACHED 

 MACROALGAE 



ZOOPLANKTON 

 AND HIGHER 

 CONSUMERS 



BACTERIA 



BENTHIC 

 COMMUNITY 



SEDIMENTS 



Figure 4-18. Schematic diagram of the organic matter cycle in the marine 

 system. 



4-52 



