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

Abstract

Aeolid nudibranchs prey on various cnidarians and incorporate nematocysts from their prey into the cnidosac, located at the tip of 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. An initial short-term experiment assessed predation by both nudibranch species, after which subsequent experiments focused exclusively on C. militaris. Short-term experiments for 24 h and long-term experiments lasting up to 258 days were conducted to determine whether C. militaris consumes a variety of cnidarians, and if it incorporates the prey nematocysts into its cnidosacs. 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 95 polyps day−1 increased with greater prey availability, but did 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 cnidosac; only nematocysts from its known hydrozoan prey were identified in the cnidosac. 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 cnidosacs. This is the first report to demonstrate complete selectivity in nematocyst sequestration over an extended feeding period in a nudibranch possessing a functional cnidosac. These findings contribute to understanding nudibranch feeding ecology and the potential role these predators may play in regulating jellyfish blooms.