Our Oceans in Peril

One sign of the troubles facing our oceans is the spread of jellyfish infestations. There seem to be two main causes of this - overfishing of species that normally feed on jellyfish and warming seas that extend their habitat.

A purple jellyfish, known as the "mauve stinger", has plagued Spanish beaches and swimmers there for some time. Tourist operators now have to sweep the beaches and close in waters to keep them free of the problem.

Last week, the mauve stinger showed up, en masse, where it's never seen - off the northeast coast of Ireland. An infestation there wiped out Ireland's only salmon farm. From The Age:

The jellyfish, covering an area of around 26 square kilometres, engulfed the Northern Salmon Company's cages off the province's north-eastern coast, suffocating 100,000 fish, the firm's managing director, John Russell, said.

"It was sheer devastation - I've been 30 years in the salmon industry and I've never seen anything like it," Mr Russell said.

Staff on their way to give the fish their morning feed noticed a "reddish-brown tinge" to the sea and then realised the boats were struggling to make headway through an expanse of jellyfish over 10 metres deep, Mr Russell said.