Predation on scyphozoan polyps and selective nematocyst incorporation dynamics in an alien aeolid nudibranch

Background Aeolid nudibranchs prey on various cnidarians and incorporate nematocysts from their prey into their cerata for self-defense. This study examined the predator-prey interactions between two nudibranch species, Caloria militaris and Flabellina affinis , and various cnidarians, focusing on scyphozoan polyps from common eastern Mediterranean medusae, including Aurelia sp. Cassiopea andromeda , Phyllorhiza punctata , and Rhopilema nomadica . Short-term experiments for 24 hours and long-term experiments lasting up to 258 days were conducted to determine whether these nudibranchs feed on a variety of cnidarians, and if they incorporate the prey nematocysts into their cerata. Results Laboratory experiments indicate that while F. affinis avoids scyphozoan polyps, C. militaris readily consumes all tested scyphozoan and hydrozoan species and can subsist on them for extended durations of up to 258 days. C. militaris predation rate, reaching 50 polyps day ^-1 increases with greater prey availability, but does not reach saturation even at very high prey abundances (>80 polyps day ^-1 ), suggesting a higher predation capacity. Surprisingly, despite this intense predation, C. militaris did not incorporate any of the scyphozoan nematocysts in its cerata; only nematocysts from its known hydrozoan prey were identified in the cerata. Conclusions C. militaris is a generalist that preys on hydrozoa and can extensively feed on a variety of scyphozoan polyps, yet it does not incorporate scyphozoan nematocysts into its cerata. This is the first report to demonstrate such complete selectivity in nudibranch nematocyst sequestration over an extended feeding period. These findings contribute to understanding nudibranch feeding ecology and the potential role these predators play in regulating jellyfish blooms.