Inter-annual dynamics in the trophic ecology of juveniles of five notothenioid fish species from the South Shetland Islands (Southern Ocean)

Abstract

The trophic ecology of several cryonotothenioid species has been well studied, but scarcely on the juvenile fraction of their populations. Particularly, till date the inter-annual variation of the diet composition and feeding habits of these young notothenioid stages has not been explored. Herein, we analysed the trophic ecology of 755 specimens of the species Notothenia rossii, Notothenia coriiceps, Nototheniops nudifrons, Trematomus newnesi and Harpagifer antarcticus, collected in the inshore waters of Potter Cove, South Shetlands Islands, during four consecutive sampling periods from 2008 to 2012. The stomach-content analysis using the IRI % and the Amundsen et al. (1996) methods provided data on feeding habits and trophic niche breadth. Our results indicate that the species are demersal and benthophagous, have a generalized type of feeding strategy and prey chiefly on demersal–benthic amphipods (mainly genus Gondogeneia and Oradarea), and on other epibenthic invertebrates associated with macroalgal beds. Significant differences were observed in the diet of all species between sampling periods, and ontogenetically, only in N. rossii and T. newnesi. According to the estimated trophic levels, the juvenile cryonotothenioids were identified as secondary consumers. Ambush feeding was the predominant feeding behaviour in all species, and in N. rossii and N. coriiceps, also grazing. Likewise, these two fish species exhibited a wider diet diversity than the other notothenioids. Using literature information on the trophic ecology of the late juvenile–adult stages of the same species at Potter Cove, we identified differences and likenesses with our results on the early juvenile–juvenile fraction of the fish community. This study highlights the key role of nearshore areas in the cryonotothenioids life cycle.