Brooding in the deep-sea sea anemoneActinostola crassicornis(Hertwig, 1882) (Cnidaria: Anthozoa: Actiniaria) from the southwestern Atlantic Ocean

Marine invertebrates can display several reproductive strategies, from external reproduction to parental care. Internal brooding is particularly relevant in harsh conditions, like Antarctic/sub-Antarctic waters and deep-sea, since it maximizes the survival of the young.Actinostola crassicornisis an abundant and widely distributed sea anemone from the southwestern Atlantic Ocean. It can be found all along the Argentinean sea down to 1200 m depth, usually in large numbers. It is a unique species in the area, since it is a large white brooding sea anemone. We studied 75 specimens collected by the O/VWalther Herwigand the O/VPuerto Deseadoall along its distribution, from about 60 m to 800 m depth, in different seasons of the year. All the specimens were sexed, and the presence of free oocytes and juveniles inside the coelenteron were assessed. Large oocytes (over 500 mu m) and juveniles were found in samples from most of the sampled months. We found a larger number of female specimens, and most of the brooding specimens were female. No early developmental stages were found smaller than a sea anemone with about 12 tentacles. We conclude thatA. crassicornisreproduces continuously throughout the year and that although most of the juveniles were found in females, male specimens can breed. Brooding has great benefits in terms of protecting the offspring, since predation upon the juveniles is prevented, but dispersal of the offspring is low, shown by the aggregated distribution of the species.