Fitness costs of alarm cues in sea urchins: Fertilization, hatching, and larval size.

Sea urchins sense alarm cues extracted from crushed conspecifics and perform anti-predation behaviors in exposure to alarm cues. This indicates of the fitness benefits of alarm cues in sea urchins. The present study investigated whether fitness costs of alarm cues exist in fertilization, hatchability, deformity, and larval size of the sea urchin Mesocentrotus nudus. In the present study, we found that fertilization and hatching rates were significantly lower in the group with alarm cues than those in the group without alarm cues, indicating that fitness costs of alarm cues exist in sea urchins. However, there was no significant difference in deformity rate, larval length, stomach length, and stomach width of M. nudus with and without alarm cues. The group with alarm cues showed significantly shorter larval width than the group without alarm cues. This indicates that smaller larvae of sea urchins more probably survive in the environment with alarm cues. The present study reveals that fitness costs of alarm cues exist in sea urchins and sheds light on the ecological roles of alarm cues in kelp bed ecosystems.