Carbon cycling in the pelagic environment

Važan dio pelagičkog ekosustava je epipelagijal, područje slobodne vode do oko 150 m dubine u kojem se razvija primarni proizvođač – fitoplankton. Fitoplankton se razvija unutar godišnjih ciklusa, a u ovisnosti o fizikalno-kemijskim i biotičkim čimbenicima. Organsku tvar u moru predstavlja čitav niz ugljikovih. Prema porijeklu može biti alohtona, donesena iz drugih sustava i autohtona, porijeklom od primarne produkcije. Autohtona organska tvar proizvedena u epipelagijalu potrebna je svim životnim zajednicama u moru a posebno onima na dnu. Pelagički sustavi imaju mehanizme recikliranja i vertikalnog prijenosa organske tvari. Taj se prijenos najčešće odvija putem agregiranja i sedimentacije organske tvari te putem hranidbenih mreža. Agregiranje organske tvari u obliku „morskog snijega“ i njeno tonjenje posljedica je cvjetanja dijatomeja. Stanice dijatomeja luče ljepljive polisaharide koji djeluju kao središta agregiranja i dok tonu na sebe vežu organsku tvar. Način prijenosa organske tvari u dubinu su i fekalne grudice zooplanktona koje sadrže neprobavljenu organsku tvar. Bakterijska razgradnja te mikrobni krug važni su za recikliranje otopljene organske tvari i njeno vraćanje u hranidbenu mrežu.Important part of pelagic environment is its upper layer, shallower than 150 m which contains the biggest biomass of primary producers – phytoplankton (photic zone). Phytoplankton develops in regular annual cycles which depend on certain physical, chemical and biological parameters. The organic matter in the sea is represented by carbon compounds. Organic matter in the sea can originate from other ecosystems (alochtonous) or it can be produced by primary producers (autochtonous). The one that is assimilated in epipelagic zone is vital for all marine ecosystems, especially for those on the bottom of the ocean. Pelagic system has mechanisms for recycling and vertical export of organic matter. It is conducted by aggregation and sedimentation of organic matter or through different food webs. Aggregation of organic metter and its sinking is taking place after large diatom blooms, and it's also called „marine snow“. „Marine snow“ is created by sticky diatom exopolimers which act as centers of aggregation. Faecal pellets of zooplankton are also very important way of vertical transport. They contain non-digested organic matter. Microbial decomposers recycle dissolved organic matter and return it into food web