Credit: R.Robbins/S. Rupp/University of Hawai?i at Manoa/Cover Images Researchers from the University of Hawai?i at Manoa have resolved a longstanding mystery of the deep by discovering how giant sea spiders reproduce. The reproduction of giant sea spiders in Antarctica has been largely unknown to researchers for more than 140 years, until now. The findings about these mysterious creatures could have wider implications for marine life and ocean ecosystems in Antarctica and around the world. Sea spiders, or pycnogonids, are a group of spider-like invertebrates found in species around the world. Most species are smaller than a fingernail, but some Antarctic species have leg spans of more than one foot! They are of special biological interest as an example of “polar gigantism” whereby some organisms in polar regions grow to much larger sizes than their relatives in warmer climates. Outlining the mysterious nature of the ocean arachnids, Professor and lead researcher Amy Moran said: “In most sea spiders, the male parent takes care of the babies by carrying them around while they develop,.What’s weird is that despite descriptions and research going back over 140 years, no one had ever seen the giant Antarctic sea spiders brooding their young or knew anything about their development.” Moran’s lab has studied polar gigantism 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 Toh and Graham Lobert, made a groundbreaking discovery. Diving under the ice, they hand-collected groups of giant sea spiders that appeared to be mating and transported them to tanks for observation. To their amazement, two different mating groups produced thousands of tiny eggs. Instead of carrying the babies until they hatched, as in most species of sea spiders, one parent (likely the father) spent two days attaching the eggs to the rocky bottom where they developed for several months before hatching as tiny larvae. “We were so lucky to be able to see this,” Toh said. “The opportunity to work directly with these amazing animals in Antarctica meant we could learn things no one had ever even guessed.” Within weeks after laying, the eggs had been 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 this before,” Lobert said. Lloyd Peck, a renowned Antarctic biologist with the British Antarctic Survey who was not involved with the study said, “The general ecology and reproductive biology of Antarctic marine species remains overwhelmingly unknown and we have data on only a handful of species, so papers like this one are of huge importance in shedding light on how animals function in one of the least studied parts of the world’s ocean.” The researchers' findings were published in Ecology in February 2024. More information available, here: https://www.hawaii.edu/news/2024/02/18/giant-antarctic-sea-spiders/.