Throughout December, hundreds of sea lions vanished from the San Francisco bay area only to show up later in the Oregon Sea Lion Caves. The Oregon Sea Lion Caves are a connected system of sea caves and caverns located along the Pacific coast of Oregon and a popular hangout for sea birds such as the tufted puffin, pigeon guillemot, Brandt’s cormorant, and various types of gulls. The caves are also an important wintering home for the Stellar Sea Lion and – to a lesser extent –the California Sea Lion.

“We’re seeing the sea lions coming up this way from California because of the feeding. If the cold water fish move north to find colder waters, the sea lions have to eat and they follow the fish wherever they go,” says Sea Lion Caves General Manager Dan Harkins.

So, how can the cave staff know for sure who’s a visitor from California and who isn’t? Apparently, sea lions have dialects; just like us humans.

“We can identify them by the sound of their voice. They have a barking noise rather than a grumbling or a growling that Stellers do,” says Harkins.

The Sea Lion Caves were first explored in 1880 by local resident Captain William Cox. On a calm day, the captain entered the grotto through the western channel in his small boat. During a later expedition he was reportedly marooned due to stormy weather and had to survive by shooting a sea lion and eating its flippers. In 1887 Captain Cox purchased the land from the State of Oregon and the cave system has been privately owned and managed ever since.

The invasive kelp Undaria pinnatifida is has now spread from Los Angeles to San Francisco Bay, despite eradication efforts.

Earlier, the northward spread of this sea weed – which can grow an inch a day and forms dense underwater forests – was believed to have been stopped at Monterey Bay, but this assumption turned out to be wrong when a biologist at the Smithsonian Environmental Research Center happened to notice a six-foot long piece of kelp attached to a boat in a yacht harbor in San Francisco Bay.

“I was walking in San Francisco Marina, and that’s when I saw the kelp attached to a boat,” said Chela Zabin, biologist at the Smithsonian Environmental Research Center in Tiburon, California. “It was six-foot long, and there is nothing here in the bay that gets to that size. I didn’t want to believe what it was, it’s depressing.”

Further investigation showed U. pinnatifida clinging not only to boat hulls in the marina but to docks and pier pilings as well.

U. pinnatifida was discovered in Los Angeles Harbour in 2000 and within a year reports of its presence had arrived from Catalina Island and Monterey Bay. A federal eradication program was put in place, but the funding dried up last year. Since then, volunteer divers have been the only ones combating the kelp.

Five quick facts about Undaria pinnatifida

• Undaria pinnatifida is a fast growing kelp native to the waters of Japan, China and South and North Korea.

• Within its native range it is an appreciate source of food and if you’ve ever tasted miso soup, this is what you were eating. The Japanese name for this species is wakame.

• U. pinnatifida has managed to establish itself in many different regions outside its native range, such as the Atlantic coast of Europe, the Mediterranean Sea, and the Argentinean coast. By attaching itself to vessel hulls it can hitchhike across the globe in search of new suitable habitats. This kelp can also enter ecosystems via imported oysters, and some people deliberately or accidently introduce U. pinnatifida to local ecosystems by cultivating it for cooking purposes.

• When U. pinnatifida spread to ecosystems not used to its presence, it can grow uncontrolled and prevent native kelp species from getting any sunlight. This can disturb the entire ecosystem.

• U. pinnatifida has been nominated to the list “100 worst invasive species in the world”.