Shallow Water Sightings Challenge Established Depth Models for Giant Phantom Jellyfish

The elusive *Stygiomedusa gigantea*, or giant phantom jellyfish, is prompting a re-evaluation of established deep-sea distribution models following recent shallow-water observations. This large cnidarian, which can possess a bell exceeding one meter in diameter and oral arms extending over ten meters, has historically been documented infrequently, with approximately 126 confirmed encounters recorded since its initial description in 1910. Research utilizing remotely operated vehicles (ROVs), notably by institutions such as the Monterey Bay Aquarium Research Institute (MBARI), has been essential for observing the species intact, as conventional trawl nets often compromise its delicate structure.

For decades, the scientific consensus positioned the giant phantom jellyfish within the bathypelagic zone, typically between 1,000 and 3,000 meters deep. However, recent investigations, particularly in high southern latitudes, are compelling scientists to reconsider this vertical range. A study published in the journal *Polar Research* documented several encounters with *S. gigantea* off the Antarctic Peninsula at significantly shallower depths, specifically between 80 and 280 meters. These observations occurred during the inaugural Antarctic season of the Viking Expeditions vessel, the *Viking Octantis*, in early 2022, using submersibles deployed from the ship.

Scientists are currently theorizing that these shallower appearances may correlate with seasonal environmental shifts characteristic of the Antarctic region. The working hypothesis suggests that fluctuations in prey availability, such as the enhanced zooplankton biomass present from early spring through early summer, could be drawing these major invertebrate predators upward from the deeper midnight zone. As a deep-sea predator, the species competes with squids and whales, with its diet consisting mainly of plankton and small fish. The data gathered by the Viking Expedition Team, which included Chief Scientists such as Dr. Daniel Moore, underscores the utility of personal submersibles in probing previously inaccessible polar waters for biological research.

Beyond its predatory function, the giant phantom jellyfish participates in notable ecological interactions. In the Gulf of California, the pelagic brotula fish, *Thalassobathia pelagica*, has been observed using the jellyfish's large bell as a shelter, illustrating the species' importance as a micro-habitat. This association is further supported by evidence suggesting the fish may assist the jellyfish by removing parasites. The species maintains a cosmopolitan distribution, having been documented in all global oceans except the Arctic Ocean. While sightings in mid- and low-latitudes remain bathypelagic or mesopelagic, the pattern of shallower occurrences in high latitudes suggests that temperature or light avoidance may influence its vertical positioning in those specific environments.

The ongoing deployment of advanced ROVs by organizations like MBARI, which has recorded nine sightings over 34 years, alongside the use of expedition cruise vessels, continues to open new avenues for understanding this enigmatic, non-stinging gelatinous giant.