Giant Antarctic sea spiders 140-year-old reproductive mystery solved by UH researchers

by Marc Arakaki, University of Hawai’i Manoa
February 18, 2024

The reproduction of giant sea spiders in Antarctica has been largely unknown to researchers for more than 140 years, until now. University of Hawaiʻi at Mānoa scientists traveled to the remote continent and saw first-hand the behaviors of these mysterious creatures, and their findings 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 marine habitats globally. Most species are smaller than a fingernail, but some Antarctic species have leg spans (tip of one leg to the tip of the opposite leg) of more than a foot. These animals are a famous example of “polar gigantism,” 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 babies by carrying them around while they develop,” UH Mānoa School of Life Sciences Professor and lead researcher Amy Moran said. “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. The researchers findings were published in Ecology in February 2024.

Keep reading: https://manoa.hawaii.edu/news/article.php?aId=13079

Read the Ecology paper: https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.4258