On the significance of Antarctic jellyfish as food for Adelie penguins, as revealed by video loggers

Concern of pelagic gelatinous organisms taking over perturbed marine ecosystems has led to a recent increase in research into this group. However, the significance of this group as prey remains challenging to assess, and hence, gelatinous consumers are often depicted incorrectly as dead ends of pelagic food webs. In the Southern Ocean, where a shift in trophic webs may favour gelatinous animals, we video-monitored prey intake of a key predator. Twenty-eight chick-rearing Adelie penguins Pygoscelis adeliae from Dumont d'Urville station (66 degrees 40'S, 140 degrees 01'E) were instrumented with miniaturized video loggers in 2014-2015. Among other items (krill, fish), 101 gelatinous organisms (n = 79 jellyfish, 6 salps and 16 unidentified) were observed on 13 of 21 exploitable video footages (total: 59 h). Importantly, 65.3 % of gelatinous organisms were attacked, but among them salps were not attacked. Attacks on jellyfish were significantly associated with the visible presence of the jellyfish's gonad. Jellyfish were encountered at an average depth of 26.2 +/- 10.4 m, significantly shallower than krill. Attacks occurred mostly during bottom, but also descent or ascent dive phases. Concomitant GPS location for four birds revealed that attacks on jellyfish occurred above the shelf, 35 km north from the colony, where sea ice concentration reached 88 %. These results indicate that Adelie penguins occasionally feed on jellyfish, even though other prey types are also available. Refining our perception of scyphozoans' niche may thus help anticipate the functional response of the food webs to the extensive changes witnessed in the Antarctic environment.