So heres why jellyfish are increasing in numbers. Due to climate change, rising Co2 levels and temperatures in the ocean are causing plant based plankton or phytoplankton to increase. This in turn has helped to feed animal based plankton or photoplankton,which is what jellyfish eat. With food levels for jellies increasing worldwide I'd say jellies are not going away anytime soon. Overfishing is not a large contributing factor. Nutrients from agricultural run off, sewage treatment facilities,basically any nutrients from land combined with higher Co2 and temps are a recipe for jellyfish.
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