causes phytoplankton blooms. tiny algae which form huge carpets as can be seen from space. vegetable fodder produces all the more zooplankton. it's made up of microscopically small animals and fish larvae. this is what jellyfish feed on allowing them to reproduce in great numbers this is causing you trophic conditions with loss of nutrients in the water it leads to low oxygen levels and. jellyfish are very tolerant of those conditions. at the same time the fishing industry has depleted fish populations and fish are the main food competitors of jellyfish. fishing in the baltic and the danish research boat down a. even