Jellyfishes have become more abundant in the ocean over recent decades. Jellyfish blooms seem to be related to human induced stresses like overfishing, habitat modification, eutrophication, and climate change. The combination of these factors act synergistically to create a habitat that is more favorable for jellyfishes. Global climate change accelerates jellyfish growth, eutrophication leads to jellyfish outbreak, removing their competitors due overfishing makes them more successful, and transporting them to other places enhances their chances of colonization of new areas. Jellyfish are important components of oceanic environments, and can influence community composition by their increase. Eventhough aggregations of jellyfish are considered normal and a component of a natural and healthy environment, an increase in frequency of jellyfish has been observed. Direct management action is needed in order to prevent a large-scale alteration of more pelagic systems throughout the world’s oceans. Research is crucial on jellyfish ecology and their life cycles, as well as control over eutrophication and ballast water transportation.
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