Three signs your ocean might need help:

1) Thousands of jellyfish wash up on your coast. The Namibian coast used be flourishing in fish. Not anymore:

Now it is entirely dominated by jellyfish. Things appear to be going that way in the Middle East, South Pacific, the Gulf of Mexico and the Mediterranean.

The Japanese coast has long weathered jellyfish blooms, but they tended to happen about once every 35 years. Since 2002, however, every year but one has seen massive blooms.

... Overfishing may cause blooms: some fish eat baby jellyfish, and some, like herring, compete with jellyfish for the same zooplankton food. Take the fish away, and you get more jellyfish.

But jellyfish also eat fish eggs and baby fish, so if they start to increase in a marine ecosystem, it can create a positive feedback loop and produce more jellyfish at the expense of the fish. The jellyfish don’t allow fish stocks to recover because they are eating all the baby fish before they get large enough to reproduce. -- The Economist

2) Staple-diet fish vanish:

The National Marine Fisheries Service stated that 25% of fish stocks appearing in American waters were overfished (insofar as they can be categorised; for many more types of fish, officials do not have enough information to determine their status). If even America cannot keep its fisheries in robust health, imagine the problems offshore of India or Africa.

The bad news is that there may be very few fish in the sea left within a few decades. The North Sea cod, once a staple of English fish & chips, is now largely gone. Al Gore, the green knight, found himself in trouble recently when People magazine reported that Chilean sea bass—one of the most notoriously overfished species in the world—was on the menu at a rehearsal dinner ahead of his daughter’s wedding. His spokesperson has since calmed the eco-outraged by explaining that the sea bass originated from one of the few sustainable fisheries for that species. -- The Economist

3) Coral starts to crumble to dust:

2005 and 1998 were the two most damaging years for coral reefs in recorded history; they were also the world’s hottest years since records started in1880. About 16% of the world’s reefs were effectively lost in the Indian Ocean and Western Pacific in 1998, and in 2005, massive coral losses occurred in the Caribbean; all due to coral bleaching. -- The United Nations Environment Programme

There is growing concern that carbon dioxide emissions will increase the acidity of seas and oceans. This in turn may impact calcium and shell-forming marine life including corals but also tiny ones such as planktonic organisms at the base of the food chain....

Increasing concentrations of C02 in the atmosphere are likely to be mirrored by increasing acidification of the marine environment. Increasing acidification may reduce the availability of calcium carbonates in seawater, including a key one known as aragonite, which is used, by a variety of organisms for shell-building. Cold-water and deep water corals could be affected by acidification by 2050 and shell-building organisms throughout the Southern Ocean and into the sub-Arctic Pacific Ocean by 2100. – The United Nations Environmental Programme

If nothing is done, all we will have left is seas of garbage and videos of pleasures past:

 

Further Reading:

• An Ocean of Unknown
• Synthetic Sea