Autumn trophic niche partitioning reduces interspecific competition between co-existing Antarctic Krill (Euphausia superba) and hyperiid amphipod (Themisto gaudichaudii)
摘要
As key species in Antarctic and sub-Antarctic ecosystems, Antarctic krill (Euphausia superba) and hyperiid amphipod (Themisto gaudichaudii) overlaps in distribution, and the overlapping level may further increase with global climate change, resulting in competitive feeding pressures between them. Combining fatty acid and stomach content microscopy, we investigated the autumn food composition and ecological niche of E. superba and T. gaudichaudii across the shelf, shelf slope, and oceanic region along the northern South Orkney Islands. The results suggested partial overlap in food resources of E. superba and T. gaudichaudii, yet their trophic niches were largely distinct. Euphausia superba was omnivorous detritus-preferring consumers, and the flexible feeding strategy helped to expand their trophic niche width. Adult T. gaudichaudii was carnivorous predator-preferred consumer, capable of consuming prey from different trophic levels. Variations in surface chlorophyll-a concentration and predation pressure drove E. superba to migrate to the seafloor of the shelf area for increased benthic feeding, or stay in the diatom-rich upper layers of the oceanic region. The utilization of distinct food resources facilitated trophic niche partitioning between the two species in autumn. The pelagic or benthic feeding preferences of E. superba and their degree of food competition with T. gaudichaudii appeared to be strongly correlated with surface chlorophyll-a level.