Novel feeding and mating behaviors of a population of nautiluses, Nautilus belauensis, in Palau

The nautiloid lineage extends back nearly 500 million years but today, is represented by only two living genera, Nautilus and Allonautilus. Behavioral observations of these living nautiluses have improved our understanding of how nautiloids, and ammonoids, behaved and interacted in their environment. These behaviors may also help to inform conservation practices. Here, we describe feeding and mating behaviors in wild nautiluses not reported from any other population. In Palau, Nautilus belauensis was observed actively preying on a large, living crab (Chaceon sp.) and performing courtship-like behaviors prior to mating. These behaviors occurred across multiple nights and from different nautiluses, suggesting that the behaviors are characteristic of at least a subset of the population, if not the entire population. Perhaps the behaviors exhibited by the Palauan nautiluses are an outlier and simply a localized characteristic of a far-removed population. Or, perhaps these apparent abnormal behaviors of Palauan nautiluses are what all nautiluses across the Indo-Pacific should be exhibiting. If the latter explanation is correct, we can start to address the potential causes of the behavioral differences, such as population size, habitat type, and prey availability. In either case, this apparent behavioral plasticity may have also been a reason that the nautiloid lineage has been able to survive throughout millions of years of environmental changes. Today, these behavioral observations could prove to be a valuable conservation tool to protect species and environments, especially in the deep-sea ecosystem the nautiluses inhabit.