If you're afraid of spiders, these critters are your worst nightmare: giant sea spiders, living in frigid waters in the Antarctic. Creepy as they may seem, scientists say they have a lot to teach us about an underexplored ecosystem.

The giant spiders are an example of a phenomenon found in Arctic and Antarctic waters called polar gigantism. In extremely cold deep sea environments, a variety of species, including sea spiders, have evolved to be much larger than their counterparts in warmer climates.

Giant sea spiders

Tobalski says the question of why the spiders evolved to be so large 'is going to probably remain a big question in evolutionary biology.' (submitted by Bret Tobalski)

In temperate waters in North America and Europe, sea spiders average two to three millimetres in diameter, according to Bret Tobalski, a University of Montana professor who studies the creatures.

"You practically need a magnifying glass to see them or spot them in the water," he said, "whereas in the Antarctic, where we've been working, they grow to be 30 to 35 centimetres in diameter."

Various theories exist on how polar seas allow creatures to grow to such a large size. Tobalski's team is testing one hypothesis, which suggests that the spiders have been able to grow so large because freezing temperatures have slowed their metabolism to the point where they barely need oxygen.

Understanding how the growth is possible is only part of the puzzle, though. Tobalski says that the "why" is just as important.

Bret Tobalski

Tobalski poses before an Antarctic dive. 'It’s humbling to dive there where you just get incredible diversity of organisms, and above the ice is so harsh and bleak,' he said. (submitted by Bret Tobalski)

"It's such a big question," he said. "It's of the same ilk as: 'how did animal flight evolve?'

"There's generally an underlying hypothesis that offers some selective advantage, some kind of evolutionary advantage," he said."Teasing apart what exactly that is is the question."

Tobalski said the work his team has done on the giant sea spiders is just the tip of the iceberg.

To date, Tobalski has conducted 49 dives to study the spiders. Each one allows for approximately half an hour of observation time.

"In Antarctica, it's incredible how huge the space is, and it's a great deal of money and effort just to get small samples of information from a limited location," he said. 

"It's humbling to dive there. You just get incredible diversity of organisms, and above the ice is so harsh and bleak."

'We may lose some of those species before we even discover them'

Michael Pisaric, a professor at Brock University who studies climate change, says that mysterious creatures such as giant sea spiders demonstrate what's at stake as the world grapples with climate change.

Giant sea spiders

Michael Pisaric, a researcher at Brock University, says that the spiders illustrate the fragility of undiscovered species, and the possibility that they could be affected by climate change before they're even discovered by humans. (Bret Tobalske)

"The importance of it is to really understand these systems that we really don't know a lot about," said Pisaric, "and there's probably other species out there that we simply haven't even discovered yet."

Pisaric says the estimates for the number of species in the world could range from as few as 10 million to as many as 100 million. With many of these undiscovered species living in remote regions such as the Arctic, the deep oceans and the tropical rainforest, they could be particularly susceptible to changes in the environment.

"There's probably a lot of species there that we don't know about," Pisaric explained. "As the climate changes, we may lose some of those species before we even discover them."