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The wandering grey whale that bewildered scientists after appearing off the coast of Israel last month is now paying a visit to northeastern Spain.The sighting near Barcelona Harbour means the whale, believed to be one that would normally swim past Vancouver Island, travelled about 3,000 kilometres since it was last spotted 23 days earlier.

Although scientists have not been able to positively identify where the 12-metre whale came from, the most likely scenario is that it's part of the population that would normally swim past Vancouver Island, migrating from birthing lagoons in Mexico to the Bering Sea, and that it swam through the Northwest Passage in an increasingly ice-free Arctic.

There is speculation the whale was following food -- some observers say there are signs populations are dropping, possibly because warming waters mean less food. The tiny marine life they thrive on needs cooler temperatures to survive.

Global climate change is fundamentally disrupting marine ecosystems, especially in the polar oceans, according to two new reviews of scientific research released Thursday in the journal Science.

Changes in temperature, ocean acidity and volume are affecting species from phytoplankton — the microscopic marine plants at base of the food chain — to polar bears, which may lose 68 percent of their summer habitat by 2100. "Climate change is affecting an enormously wide range of physical and biological aspects of the ocean," said John Bruno, a University of North Carolina marine ecologist and co-author of one of the reviews. "Once you start tweaking temperature, everything changes." Photosynthesis by phytoplankton is down six percent since the 1980s, and the organisms themselves are getting smaller thanks to warmer temperatures, the review noted.

Less plankton means less food for fish, which in turn means less seafood for human consumption. Phytoplankton also absorb carbon dioxide from the air and sequester it at the seafloor when they die and sink to the bottom of the ocean. Fewer phytoplankton could mean more human carbon dioxide emissions stay in the atmosphere, Bruno said, further exacerbating the climate change problem.

Plankton, base of ocean food web, in big decline

Despite their tiny size, plant plankton found in the world's oceans are crucial to much of life on Earth. They are the foundation of the bountiful marine food web, produce half the world's oxygen and suck up harmful carbon dioxide. And they are declining sharply. Worldwide phytoplankton levels are down 40 percent since the 1950s, according to a study published Wednesday in the journal Nature. The likely cause is global warming, which makes it hard for the plant plankton to get vital nutrients, researchers say. The numbers are both staggering and disturbing, say the Canadian scientists who did the study and a top U.S. government scientist. "It's concerning because phytoplankton is the basic currency for everything going on in the ocean," said Dalhousie University biology professor Boris Worm, a study co-author. "It's almost like a recession ... that has been going on for decades."

Half a million datapoints dating to 1899 show that plant plankton levels in nearly all of the world's oceans started to drop in the 1950s. The biggest changes are in the Arctic, southern and equatorial Atlantic and equatorial Pacific oceans. Only the Indian Ocean is not showing a decline. The study's authors said it's too early to say that plant plankton is on the verge of vanishing. Virginia Burkett, the chief climate change scientist for U.S. Geological Survey, said the plankton numbers are worrisome and show problems that can't be seen just by watching bigger more charismatic species like dolphins or whales. "These tiny species are indicating that large-scale changes in the ocean are affecting the primary productivity of the planet," said Burkett, who wasn't involved in the study.