34-armed Starfish

Diving with multi-armed sun stars requires specialist drysuit training and polar diving experience, as encounters take place in sub-zero water temperatures ranging from -1.8°C to 2°C. Maintain impeccable neutral buoyancy to prevent touching the sensitive benthic community or kicking up fine glacial silt, which rapidly degrades visibility. When approaching, do not touch or prod the animal; while resilient, its delicate arms and pedicellariae can be stressed or torn by clumsy contact. For underwater photographers, a wide-angle or close-focus wide-angle lens with twin strobes is ideal to capture the animal's impressive diameter against scenic polar backdrops. Take care to angle your lighting outward to minimise backscatter from suspended glacial flour and rich plankton in the water. Always monitor your drysuit inflation and dive computers closely in extreme cold.

The optimal window to encounter the Antarctic sun star coincides with the austral summer expedition season running from November through to March. During these months, ice-strengthened expedition vessels and polar liveaboards navigate the Antarctic Peninsula, South Georgia, and the South Shetland Islands. In early summer (November to December), underwater visibility is frequently at its peak before seasonal phytoplankton blooms develop, providing crystal-clear vistas across polar drop-offs and rocky bottoms. By late summer (February to March), retreating sea ice opens up access to southern dive sites further down the western Antarctic Peninsula, such as Paradise Bay and the Lemaire Channel, where these remarkable echinoderms thrive across untouched circumpolar seafloors.

This species inhabits the frigid marine environments of the Southern Ocean, extending from the coastal margins of the Antarctic Peninsula and continental shelf to sub-Antarctic archipelagos including South Georgia, the South Sandwich Islands, and the Kerguelen Plateau. It is predominantly benthic, thriving across diverse underwater substrates ranging from vertical drop-offs and bedrock reefs encrusted with sessile filter-feeders to morainic gravel, boulder fields, and fine glacial sediment plains. The species displays a remarkably broad bathymetric distribution, occurring in shallow coastal waters from just 5 metres beneath the ice down to abyssal depths exceeding 600 metres. It prefers dynamic polar zones where strong currents transport fresh plankton and krill across the seafloor.

The Antarctic sun star is a formidable and aggressive benthic carnivore that relies on both active suspension hunting and ground scavenging. Its diet consists predominantly of mobile and sessile invertebrates, including krill, amphipods, mysids, small benthic fish, ophiuroids (brittle stars), and other sea stars. When hunting, it raises its numerous flexible arms high into the passing current, presenting a lethal forest of predatory pedicellariae. These microscopic, jaw-like pincers snap shut instantly upon contacting passing macrozooplankton or fish larvae, trapping the prey securely. The starfish then flexes its arms inward to draw the captured meal towards its centrally positioned mouth. In addition to snaring active prey from the water column, it readily scours the seabed for carrion, detritus, and sluggish molluscs, feeding continuously throughout day and night.