Neoichnological analysis of sea stars in the deep sea near the Aleutian Trench: behavioral insights from in situ observations

The study of biogenic structures (e.g., lebensspuren) produced by benthic fauna on the seafloor provides invaluable information about the behavior of their tracemakers. In the case of sea stars, most of the previous research has been focused on shallow-marine environments due to the extreme scarcity of data from deep-sea lebensspurens. Here, we examined sea star traces from six deep-sea stations (deeper than 4500 m) near the Aleutian Trench (North Pacific). A total of six families were identified from still images. The majority of them were not observed producing any lebensspuren or just pentameral impressions related to resting and feeding activities. Two members of the families Pterasteridae and Porcellanasteridae could be clearly characterized by a composite behavior resulting in contrasting lebensspuren morphotypes. A morphotype belonging to the genus Hymenaster undet. produced pentameral impressions (related to predation) and punctuated trails (related to podia locomotion). Members of the family Porcellanasteridae produced oval to circular impressions (that may be related to burrowing trails for the detection of organic matter), flat-shallow trails (related to podia locomotion), and irregular M-ridged trails (related to locomotion while feeding through the sediment interface). There is a severe scarcity of data related to the locomotion of past deep-sea Asteroidea (i.e., trace fossils) and their ichnotaxonomical classification. We discuss the implications of our results for the ichnofamily Biformitidae, as well as the importance of considering other features (e.g., podia impressions) rather than just hook-shaped traces related to arm locomotion.