Nudibranch Cadlina rumia discriminates waterborne cues to find prey and conspecifics and avoid threats

Abstract The dorid nudibranch Cadlina rumia is a tropical western Atlantic species commonly found under boulders and that frequently preys upon the chemically defended sponge Dysidea etheria. We evaluated the ability of C. rumia to recognize waterborne chemical cues from its prey, predator, and conspecifics. Y-maze experiments with two-current choice (control - seawater and treatment - conditioned seawater) flumes were carried out using different conditioned seawater samples soaked with cues for either 1h or 6h, obtained from (1) fresh D. etheria, (2) D. etheria actively consumed, (3) D. etheria artificially damaged (simulated predation), (4) conspecific nudibranchs and (5) its potential predator, the crab Pachygrapsus transversus. Specimens of C. rumia discerned the different chemicals offered to them after a short period of bioassays (within 10 min), regardless of the soaking time. C. rumia exhibited positive attraction to chemical cues from all D. etheria prey treatments and from conspecifics, whereas negative attraction was observed in response to the chemical cues from the crab P. transversus. Our results revealed graded differences in the strength of behavioral responses to different chemical cues, with fresh sponge-conditioned seawater eliciting the strongest attraction, followed by actively consumed sponge and conspecific cues, and a less pronounced response to artificially damaged sponge. Thus, C. rumia not only recognized the chemical cues but also showed differential sensitivity to them, possibly enhancing its ability to detect and capture prey, locate mates, and avoid predators, key selective pressures shaping survival and reproductive success in its environment.