Just Another Rather Unpleasant Side Effect

Over the last 10 years, there have been increasing common and larger "blooms" of different species of Jellyfish  in polar and tropical areas in the worlds oceans. Scientists now blame the acidification of the oceans, the "evil twin" of global warming. Oceans have been taking up to 25% of the carbon dioxide that man has produced over the last 200 years. They act as a buffer for climate change. When you add mor CO2 to sea water, it becomes more acidic. This is now occurring at a rate that hasn't been seen in the last 600 million years.
So, our planet has evolved the environment which makes it possible for us to live comfortably. The oceans evolved a fragile equilibrium which made it possible for our life to have evolved to our present stage. It took eons to create the proper balance, and it is taking us only a few decades to destroy it.
Jellyfish are representative of a primitive stage in the evolution of ocean life. They flourished under conditions which exist when things are out of balance. Normally, there are blooms of jellyfish from time to time and as the local conditions change, they go back to their normal populations. This is normal.
As the oceans become more acidic and warmer, a vicious cycle has started. The jellyfish now are in a larger more persistant environment that they contribute to and continue to by their ever increasing numbers.

Already, Marine Scientists have discovered the role jellyfish have had in depleting the normal level of bacteria, which plays the major role in recycling nutrients back into the food web. While bacteria absorb carbon, nitrogen, phosphorus and other chemicals given off by fish when they die, they cannot do this with jellyfish. The jellyfish, populating the sea in ever increasing numbers, break down into biomass with especially high levels of carbon, which bacteria cannot efficiently absorb. Instead of using it as a nutrient, the bacteria exude more carbon dioxide, which is released into the atmosphere, contributing to the vicious cycle. This makes them into a kind of ecological vampire syndrome.
The acidification of the oceans is already predicted to have such a corrosive effect that unprotected shell fish will dissolve by the middle of the next century.
The implications of this are beyond our conception. Most of the sedentary calcium based rock was formed by deposits of sea life over untold eons. We are already seeing the effects of "acid rain" on limestone and marble buildings and sculptures almost before our eyes.

ship sinking 400 lb Nomura Jellyfish

Research shows that the jellyfish spike is turning the marine food cycle on its head. The creatures devour the plankton which small fish need. This restricts the the transfer of energy up the food chain, because jellyfish do not have many predators. The predators that they do have are sharks and tuna, both of which are threatened by the rise in sea temperatures, which encourage the jellyfish.
So, the reports of giant refrigerator sized, 200 kilo ship wrecking jellyfish are going to get more common place as swarms of more than 2,000 different  jellyfish species appear earlier each year and expand their populations.
Just another rather unpleasant side effect of global warming.