ABSTRACT This communication describes the first records of byssal hairs on the postlarvae shells of Mytilus edulis platensis d’Orbigny, 1842. The postlarvae used in this study were sampled on artificial collectors used for mussel culture in San Jorge Gulf, Sudoccidental Atlantic Ocean. A general description of the hairs is made as well as an exploratory analysis of their spatial distribution on the shell surface. The presence of these byssal hairs is suggested as a criterion to differentiate M. edulis platensis from other mytilids.

Stomach content analysis was performed on 313 juveniles of Lithodes santolla, with carapace lengths (CL) measuring between 8.40 and 49.04 mm. The influence of season, sex, size and moult stage on their diet were studied. Crabs were captured seasonally from the rocky sublittoral zone in the central area of San Jorge Gulf using SC-UBA. The frequency of prey occurrence (FO), relative abundance (RA), degree of fullness and the stomach content weight were registered. Empty stomachs were found in 14.4% of the specimens, while stomach fullness below 50% occurred in 55.0% of crabs and over 50% in 30.6% of crabs. Juveniles did not feed prior to and immediately after moult. A total of 27 prey groups were identified, which included several species of algae, protists and invertebrates. The higher FO was observed for coralline red algae (41.5%), ophiuroids (34.8%), echinoids (25.1%), isopods (21.7%), bivalves (19.5%), polychaetes (16.6%) and bryozoans (15.0%). In terms of RA, the main prey items were ophiuroids, isopods and coralline red algae. No significant differences were found in the amount of food consumed and diet composition between sexes. A seasonal variation in the prey species composition was recorded. The diet of crabs smaller than 15 mm CL differed significantly from that of larger juveniles, due to a higher abundance of bryozoans and isopods in smaller juveniles. The great diversity of prey found in juvenile king crab indicates that they are macrophages and opportunistic omnivorous predators, which take advantage of complex rocky and biogenic subtidal habitats for food and shelter.

Se analizó el contenido estomacal de 313 ejemplares juveniles de centolla de ambos sexos con longitudes de caparazón (CL) entre 8,40 y 49,04 mm, estudiándose la influencia del sexo, talla, estado de muda y estación del año. Los animales fueron capturados mediante buceo en muestreos estacionales en el infralitoral rocoso del área central del Golfo San Jorge. Se determinó la frecuencia de ocurrencia (FO) y abundancia relativa (AR) de las presas halladas, estado de repleción y peso del contenido estomacal. Se registró un 14,4% de animales con el estómago vacío, un 55,1% con repleción menor del 50% y un 30,5% mayor al 50%. Los juveniles no se alimentan antes de mudar, durante la muda ni en postmuda reciente. Se identificaron 27 grupos de presas diferentes, incluidas varias especies de algas, protistas e invertebrados. Las mayores FO fueron registradas en algas coralináceas (45,1%), ofiuroideos (34,8%), equinoideos (25,1%), isópodos (21,7%), moluscos bivalvos (19,5%), poliquetos (16,9%) y briozoos (15%). En términos de AR, los principales componentes de la dieta fueron ofiuroideos, isópodos y coralinaceas. La composición de la dieta es diferente en animales menores de 15 mm CL de aquellos mayores a esa talla, debido a la mayor abundancia de isópodos y briozoos en este intervalo. La gran diversidad de presas registradas indica que los juveniles son esencialmente depredadores macrófagos y omnívoros, que aprovechan los complejos hábitats infralitorales rocosos y biogénicos del área estudiada para su alimentación y refugio durante los primeros años de vida.