Thick mangroves have long protected Karachi, southern Pakistan's sprawling metropolis, from battering by the Arabian Sea, but pollution, badly managed irrigation and years of illegal logging have left this natural barrier in a parlous state.

Experts fear that loss of the natural barrier formed by the mangroves could put the city of nearly 20 million people at greater risk from violent storms and even tsunamis.

A giant bluefin tuna sold for more than $37,000 in the first auction of the year at a Tokyo fish market on Monday, as Japan faces growing pressure to cut back on consumption of the threatened fish.

The 180.4-kilogram (380 pound) tuna, caught off Japan's northern region of Aomori, fetched a winning bid of 4.51 million yen ($37,480), said an official at the Tsukiji fish market.

Air pollution in Beijing dropped slightly last year, municipal authorities said, although levels of the most dangerous small particulate matter remained more than three times the internationally recommended limit.

China's cities are often hit by heavy pollution, blamed on coal-burning by power stations and industry, as well as vehicle use, and it has become a major source of discontent with the ruling Communist Party.

Two Polish teams will search this year for the Polish submarine ORP Orzel, which disappeared in the North Sea in May 1940 during a mission with the Allies in World War II.

The two searches will be conducted by the Culture Ministry and the Maritime Museum in the Baltic port of Gdansk.

Much of America is about to get the Arctic shivers.

Meteorologists are forecasting frigid polar air will plunge much of the central and eastern U.S. into sub-freezing temperatures next week.

A newborn orca in the endangered pod that frequents Puget Sound is an encouraging sign following the death earlier this month of a pregnant killer whale from the same group.

"That was a pretty hard hit," Howard Garrett of the Whidbey Island-based Orca Network said Wednesday. "It's good to see a positive sign."

In the depths of an Indonesian rainforest, scientists have identified the first known frog that gives birth to tadpoles instead of laying eggs, according to research.

Known as Limnonectes larvaepartus, this member of the Asian group of fanged frogs was first discovered decades ago by Indonesian researcher Djoko Iskandar.

Boris Morukov, a Russian cosmonaut and doctor who led an extraordinary experiment in which volunteers simulated a flight to Mars while never leaving a Moscow car park, has died at 64, his scientific institute said Friday.

"We announce with grief that Boris Morukov died suddenly on New Year's Eve," Moscow's Institute of Biomedical Problems, where Morukov was deputy director, said on its website.

Angry Maasai herders in Tanzania killed six lions that had attacked livestock, in the latest clash between man and beast in the region.

The government said it was "saddened to learn that six lions, an endangered species" were killed overnight Thursday in the northern Babati District, adding it would attempt to identify and prosecute those responsible.

Six Chinese companies have been fined $26 million for discharging tens of thousands of tonnes of waste chemicals into rivers, state media said, the biggest such penalty ever in China.

The firms in Taizhou in the eastern province of Jiangsu were sued by a local environment protection organisation and were found to have dumped 25,000 tonnes of waste hydrochloric acid into two rivers, the Xinhua news agency reported.