140-Year-Old Mystery of Giant Antarctic Sea Spiders and Their Tiny Eggs Finally Unraveled

Scientists have finally unraveled a 140-year-old mystery regarding how giant Antarctic sea spiders take care of their tiny eggs.

Giant Antarctic Sea Spiders

These marine arthropods dwell in oceans across the world. They have eight thin and extremely long legs that make them similar to daddy long legs, despite being unrelated to them.

Several sea spiders reach up to an inch in length. However, those that dwell in the poles, like the giant Antarctic sea spiders (Colossendeis megalonyx), can have lengths that reach 51 centimeters in a phenomenon known as polar gigantism. This is because they are remarkably larger compared to sea spiders in climates that are warmer.

Sea spiders are some of the few marine arthropods whose males are the exclusive carers for offspring. Amy Moran, the new study's lead author and a professor from the School of Life Sciences at the University of Hawai'i, explains that for most sea spiders, the male parent is the one who cares for the babies by carrying them as they grow.

Though sea spider reproductive strategy research goes back a full 140 years, the behavior of breeding across three out of 11 recognized sea spider families has not been observed. This includes the C. megalonyx family.

How Giant Antarctic Sea Spiders Take Care of Their Tiny Eggs

To examine how the said sea spiders care for their eggs, divers went into the chilly waters in Antarctica's McMurdo Sound. They hand-gathered individuals of C. megalonyx that apparently mated in groups. The pairs were then brought to the McMurdo Station research facility. The arachnids were kept in tanks for behavioral observation.

Efforts were documented in the "Spawning and larval development of Colossendeis megalonyx, a giant Antarctic sea spider" study. Two distinct mating pairs were observed to lay thousands of eggs at the tank's bottom. However, one parent, which was likely the male, spent two days linking the brood to the tank floor. This is in contrast to the typical carrying of eggs that other sea spiders do.

A few weeks later, the eggs were apparently algae-covered, making it difficult for them to see in the tank. In wild settings, overgrown algae could aid in camouflaging the eggs against the floor. According to Graham Lobert, a PhD student and co-author of the study, they could hardly see the eggs despite being aware of the eggs' presence. This could be why researchers were never able to witness such a phenomenon.

Ming Wei Aaron Toh, a co-author of the study and a doctoral student from the school, explains that they were lucky to witness this. Antarctic biologist Lloyd Peck from the British Antarctic Survey, who did not participate in the study, notes that the Antarctic marine species' general reproductive biology and ecology stays largely unknown. There are only a handful of species with available data. Hence, studies like this are crucial in shedding light on animal functions in one of the areas of the ocean that are least studied.

Check out more news and information on Environment & Climate in Science Times.