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The reproduction of giant sea spiders in Antarctica has been largely unknown to researchers for more than 140 years. Scientists from the University of Hawaii at Mānoa traveled to the remote continent and observed the behavior of these mysterious creatures for the first time, and their findings could have far-reaching implications for marine life and marine ecosystems in Antarctica and around the world.

Sea spiders, or pycnogonids, are a group of arachnid-like invertebrates found in marine habitats worldwide. Most species are shorter than a fingernail, but some Antarctic species have leg lengths (tip of one leg to tip of the opposite leg) of more than a foot. These animals are a famous example of “polar giantism,” a phenomenon where certain organisms in polar regions, such as the Arctic and Antarctic, grow to much larger sizes than their relatives in warmer climates.

“In most sea spiders, the male parent takes care of the young by carrying them around as they grow,” said Amy Moran, professor and lead researcher at UH Manoa School of Life Sciences. “What’s strange is that despite 140 years of description and research, no one has ever seen Antarctic sea spiders rearing their young or known anything about their development.”

Moran’s lab has studied polar giants for more than a decade. In October 2021, during a field research expedition to Antarctica, the team, including Moran and School of Life Sciences PhD students Aaron Tu and Graham Labert, made an important discovery. Diving under the ice, they hand-collected groups of giant sea spiders that appeared to be mating and carried them into tanks for observation.

To their surprise, two different mating groups produced thousands of tiny eggs. Instead of carrying the young until they hatch, as in most species of sea spiders, a parent (presumably the father) spends two days attaching the eggs to the rocky substrate where they hatch before hatching as tiny larvae. It took several months to develop. The researchers’ findings were published in Environment In February 2024.

“We were very lucky to be able to see it,” Toh said. “The opportunity to work directly with these amazing animals in Antarctica meant we could learn things that no one would have thought possible.”

Within weeks of being laid, the eggs were overgrown with microscopic algae, providing perfect camouflage.

“We could hardly see the eggs even when we knew they were there, which is probably why researchers had never seen them before,” Labert said.

Lloyd Peck, an Antarctic biologist with the British Antarctic Survey who was not involved in the study, said, “The general ecology and reproductive biology of Antarctic marine species is largely unknown and we only have data for a handful of species, so such The papers are crucial in shedding light on how animals function in one of the least studied parts of the world’s oceans.”

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