Parental care in Antarctic sea spiders | Polarjournal
Groundbreaking study reveals parental care in giant Antarctic sea spiders. (Photo: Rob Robbins)

Researchers at the University of Hawaii at Manoa have uncovered the long-hidden reproductive habits of giant sea spiders in Antarctica, solving a mystery that has puzzled scientists for over 140 years.

A new discovery shows that male Antarctic sea spiders care for their young in the icy waters of the Antarctic. Emerging from the depths of one of the oceans’ last frontiers, this discovery challenges our understanding of how marine life reproduces, particularly in the enigmatic realm of the giant Antarctic sea spiders, also known as Pycnogonida.

The findings, published in the journal Ecology on February 11, 2024, “could have far-reaching implications for marine life and ecosystems in Antarctica and around the world,” researchers said.

Giant Antarctic sea spider, aka Pynogonida (Photo: Rob. Robbins)

Sea spiders are a group of spider-like looking invertebrates that occur in marine habitats worldwide. Most species are less the size of a fingernail, but some Antarctic species reach a legspan of more than 30 centimeters.

Discovery in the icy depths

Antarctica, known for its harsh conditions and unique ecosystems, has long fascinated scientists. The recent expedition led by ecologist Amy Moran and her team has now shed new light on these captivating sea spiders. The newly published study shows that male sea spiders take on a caring role by protecting their eggs until they hatch. This behaviour is a sharp departure from previous observations and highlights a rare form of paternal care in the underwater world.

“In most sea spiders, the male parent takes care of the babies by carrying them around as they develop,” explained Amy Moran, professor and lead researcher at the UH Mānoa School of Life Sciences. “The strange thing is that despite descriptions and research going back over 140 years, no one has ever seen the giant Antarctic sea spiders breeding their young or knew anything about their development.”

Amy Moran on a dive where she collects a large sea spider (Photo: Rob Robbins)

The secret is out

The meticulous study involved collecting and observing these giant animals during a field expedition to Antarctica in October 2021. For more than a century, the reproductive strategies of Antarctic sea spiders were unknown to researchers.

Two mating groups of sea spiders were observed laying thousands of eggs. Instead of carrying the young to hatching, as is the case with most spider crab species, one parent, probably the father, spent two days attaching the eggs to the rocky bottom, where they developed for several months before hatching as tiny larvae. Within a few weeks of laying, the eggs were overgrown with microscopic algae, which provided perfect camouflage.

“We could barely see the eggs even when we knew they were there, which is probably why researchers had never seen this before,” said Graham Lobert.

The research team: (from left to right) Graham Lobert, Aaron Toh and Amy Moran. (Photo: Rob Robbins)

Lloyd Peck, a renowned Antarctic biologist at the British Antarctic Survey, who was not involved in the study, said: ˶This discovery, which reveals the role of male sea spiders as protective parents, represents a significant advance in our understanding of the life cycle of these mysterious creatures˝. Peck praised the study for its decisive contribution to a more comprehensive understanding of polar marine biology.

Heiner Kubny, PolarJournal

Link to the study Moran et al. (2024) Ecol 105 (3) Spawning and larval development of Colossendeis megalonyx, a giant Antarctic sea spider; /

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