This article from the Los Angeles Times describes the problems that our oceans are having. The Jellyfish are doing well. And other slimey things.
In many places—the atolls of the Pacific, the shrimp beds of the Eastern Seaboard, the fiords of Norway—some of the most advanced forms of ocean life are struggling to survive while the most primitive are thriving and spreading. Fish, corals and marine mammals are dying while algae, bacteria and jellyfish are growing unchecked. Where this pattern is most pronounced, scientists evoke a scenario of evolution running in reverse, returning to the primeval seas of hundreds of millions of years ago....
Industrial society is overdosing the oceans with basic nutrients — the nitrogen, carbon, iron and phosphorous compounds that curl out of smokestacks and tailpipes, wash into the sea from fertilized lawns and cropland, seep out of septic tanks and gush from sewer pipes.
Modern industry and agriculture produce more fixed nitrogen —— fertilizer, essentially—than all natural processes on land. Millions of tons of carbon dioxide and nitrogen oxide, produced by burning fossil fuels, enter the ocean every day.
These pollutants feed excessive growth of harmful algae and bacteria.
At the same time, overfishing and destruction of wetlands have diminished the competing sea life and natural buffers that once held the microbes and weeds in check.
The consequences are evident worldwide.
....Jellyfish are flourishing in the soup, demonstrating their ability to adapt to wholesale changes—including the growing human appetite for them. Jellyfish have been around, after all, at least 500 million years, longer than most marine animals.
Some people are ready to adapt - fisherman who find their nets filled with jellyfish sell them to the people who eat them - mostly in China and Japan.
Some problems are not so simple. Like the Lyngbya majuscula:
"The fireweed began each spring as tufts of hairy growth and spread across the seafloor fast enough to cover a football field in an hour.
When fishermen touched it, their skin broke out in searing welts. Their lips blistered and peeled. Their eyes burned and swelled shut. Water that splashed from their nets spread the inflammation to their legs and torsos."
People have gotten so good at fishing - what with "industrial fleets with sonar, satellite data and global positioning systems" the the big fish in the oceans have declined by 90% over 50 years. Meanwhile - in some places - jellyfish have had a 10-fold increase.
So we lose things - we gain things. One door closes - another door opens. In this case - the door is being shut on tuna, cod and grouper and it's being opened to squids, crabs, sea urchins, jellyfish - and other slimey things.
Nature has it's way of figuring out a balance. As people we are shutting the doors on ourselves.