Antarctica’s Giant Sea Spiders Have a Unique Way of Reproducing, Study Finds

Antarctica is a land of extremes. It is the coldest, driest, and windiest continent on Earth. It is also home to some of the most bizarre and fascinating creatures in the world.

Among them are the giant Antarctic sea spiders, also known as pycnogonids. These arachnids are not related to the spiders we know, but rather to an ancient group of marine animals that dates back to the Cambrian period, over 500 million years ago.

A team of researchers from the University of Hawai'i at Manoa decided to solve this mystery once and for all.

They embarked on a daring expedition to the frozen continent, where they braved the elements and dived into the icy waters to observe and document the behaviors of these enigmatic animals.

Their findings were published in the journal Nature in February 2024, and they revealed some surprising and fascinating insights into the hidden world of giant Antarctic sea spiders.

How Sea Spiders Mate in the Cold

One of the biggest challenges for sea spiders in Antarctica is finding a mate. The water temperature can drop below -2°C, and the sea ice can cover up to 90% of the surface area.

This makes it difficult for the animals to locate and communicate with each other. To overcome this obstacle, the researchers discovered that the sea spiders use a variety of strategies, such as chemical cues, visual signals, and tactile interactions.

The researchers found that the sea spiders release pheromones, or chemical substances, into the water to attract potential partners.

They also use their bright colors, such as red, orange, and yellow, to stand out from the background and signal their readiness to mate. Additionally, they use their long legs to touch and explore each other, and to form pairs or groups.

Once a pair is formed, the researchers observed that the sea spiders engage in a complex and prolonged mating ritual. The male wraps his legs around the female and inserts his sperm into her genital opening, located on the fourth pair of legs.

The sperm then travels through a tube to the ovaries, where the eggs are fertilized. The fertilization process can take up to several hours, and the pair remains attached throughout.

How Sea Spiders Care for Their Young

Another challenge for sea spiders in Antarctica is caring for their young. The water temperature is too cold for the eggs to develop on their own, and the predators are too abundant for the eggs to be left unguarded.

To overcome this challenge, the researchers discovered that the sea spiders exhibit a remarkable form of parental care, unlike any other arachnid.

The researchers found that the sea spiders transfer the eggs from the female to the male after fertilization. The male then carries the eggs on his legs, sometimes up to 2,000 at a time, and protects them until they hatch.

The male also provides oxygen and nutrients to the eggs by moving his legs and exposing them to the water currents. The male does not feed or mate during this period, which can last up to several months.

The researchers also found that the sea spiders have a unique way of dealing with the changing seasons. During the winter, when the sea ice covers most of the surface, the male sea spiders migrate to deeper waters, where the temperature is more stable and the predators are less frequent.

They also enter a state of dormancy, or reduced metabolic activity, to conserve energy and prolong their survival. During the summer, when the sea ice melts and the food becomes more abundant, the male sea spiders return to the shallower waters, where they release the hatchlings and resume feeding and mating.

Why Sea Spiders Matter for Antarctica and Beyond

The researchers concluded that the giant Antarctic sea spiders are a remarkable example of how life can adapt and thrive in extreme environments.

They also highlighted the importance of these animals for the Antarctic ecosystem and the global climate. The sea spiders are not only predators, but also prey for other animals, such as fish, seals, and penguins.

They also play a role in the carbon cycle, by consuming organic matter and releasing carbon dioxide into the water, which can then be absorbed by the sea ice and the atmosphere.

The researchers also warned that the sea spiders are vulnerable to the effects of climate change, such as warming, acidification, and pollution of the ocean.

These factors could disrupt their mating, reproduction, and survival, and have cascading consequences for the Antarctic food web and the global carbon balance.

The giant Antarctic sea spiders are a biological marvel, a polar gigantism unleashed, and a hidden world waiting to be explored.

They are a testament to the diversity and resilience of life on Earth, and a reminder of the fragility and interconnectedness of our planet. They are a mystery that has been solved, but also a mystery that remains.