Negative impact of tuna cages on environment

Tovilišta tuna su se razvila i proširila svijetom u kratkom periodu te su izgurala klasični ribolov kao večinski izvor tune na tržištu. Kao jednoj od najunosnijih i globalno raširenih grana akvakulture sve se više pažnje pridaodaje njihovom utjecaju na okoliš. Iako se za rad i održavanje ribljih kaveza ne koriste nikakve toksične tvari njihov negativni utjecaj na okoliš proizlazi iz velike količine organskog otpada u obliku ribljeg izmeta i ostataka hrane. Područja oko kaveza su opčenito okarakterizirana povišenom bioprodukcijom i smanjenom koncentracijom kisika, a utjecaj ribljih kaveza se može osjetiti i do kilometar udaljenosti. Pronađene su povišene koncentracije otopljenog dušika i ugljika, a u sedimentu se redovito nalaze povečane količine fosfora i sulfatnih iona kao rezultat rada bakterija u anoksičnim uvjetima. Osim u sedimentu anoksični uvjeti mogu zavladati i u moru u slučaju da su struje slabe ili nepostojeće, a da je opterečenje dovoljno veliko što može uzrokovati velike ekološke štete. Takve promjene u okolišu imaju snažan utjecaj na lokalnu zajednicu, mjenjajući njezin sastav, a mogu i u potpunosti izbrisati pojedine vrste. Jedan od najugroženijih ekosustava je onaj koji ovisi o primarnoj produkciji posedonije (Posidonia oceanica) koja je izrazito osjetljiva na promjene u sedimentu te negativno reagira na njih i na udaljenosti od 400 m od ribljih kaveza. Povlačenjem posedonije stanište gubi velik broj mladih riba i člankonožaca koje u livadama posidonije pronalaze utočište i hranuTuna cages developed and spread over the world in a short period of time and replaced classical fishing as the major source of tuna in the market. As one of the most profitable and globaly spred branches of aquaculture, it's impact on the environment is being increasingly called attention to. Even though no toxic substences are used to maintain fish cages, they produce large amounts of organic waste in the form of fish excrement and food leftovers, thus leading to a negative environmental impact. The areas around cages are generally characterised by increased levels of bioproduction and reduced concentrations of oxygen, an impact of fish cages that can be felt up to a kilometer away. Elevated concentrations of nitrogen and carbon have also been found in the water. Increased amounts of phophorus and sulfate ions, as a result of bacterial function in anaerobic conditions, are often found in the sediment. Other than the sediment, anaerobic conditions can occur in the sea in the case of currents being week or non-existing and the organic load being high enough, which can cause great environmental dammage. This sort of changes in the environment have a strong impact on the local biological community, changing it's composition and sometimes even erasing certain species altogether. One of the most endangered ecosystems are ones that depend on primary production of posidonia (Posidonia organica) which is extreemly sensitive to changes in the sendiment and reacts badly to them even at a distance of 400 meters from a fish cage. The retreat of posidonia means that a number of small fish and arthropods living in the plains of posidonia will have lost their source of food and shelter