The first feeding study of tropical Australia’s Irukandji box jellyfish has found that they actively fish. They attract larval fish by twitching their extended tentacles, highlighting their nematocyst clusters (stinging structures) and using them as lures. It’s an impressive feat by any standards, but particularly so for an animal that doesn’t have a defined brain.
“They’re not opportunistically grazing — they’re deliberately fishing. They’re targeting and catching fish that are at times as big as they are, and are far more complex animals. This is a really neat animal that is displaying a surprisingly complex prey capture strategy.”
The researchers were able to catch Carukia barnesi in the act by filming them through a full day and night cycle, using infrared-sensitive equipment to record behavior in times of complete darkness.
Abstract:Adult Carukia barnesi medusae feed predominantly on larval fish; however, their mode of prey capture seems more complex than previously described. Our findings revealed that during light conditions, this species extends its tentacles and ‘twitches’ them frequently. This highlights the lure-like nematocyst clusters in the water column, which actively attract larval fish that are consequently stung and consumed. This fishing behavior was not observed during dark conditions, presumably to reduce energy expenditure when they are not luring visually oriented prey. We found that larger medusae have longer tentacles; however, the spacing between the nematocyst clusters is not dependent on size, suggesting that the spacing of the nematocyst clusters is important for prey capture. Additionally, larger specimens twitch their tentacles more frequently than small specimens, which correlate with their recent ontogenetic prey shift from plankton to larval fish. These results indicate that adult medusae of C. barnesi are not opportunistically grazing in the water column, but instead utilize sophisticated prey capture techniques to specifically target larval fish. –
Robert Courtney, Nik Sachlikidis, Rhondda Jones, Jamie Seymour. Prey Capture Ecology of the Cubozoan Carukia barnesi. PLOS ONE, 2015; 10 (5): e0124256 DOI: 10.1371/journal.pone.0124256
See also: Animal mind
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