Antarctic krill Euphausia superba, crystal krill E. crystallorophias, and Antarctic silverfish Pleuragramma antarctica are key mid-trophic level species in the Ross Sea, connecting primary production to the upper trophic levels. Distributions of these species were constructed from observations made in the western Ross Sea from 1988 to 2004. Distributions of environmental conditions were obtained from a 5-km resolution circulation model (temperature, mixed layer depth, surface speed) and satellite-derived observations (chlorophyll, sea ice cover). A hierarchy of statistical methods determined correlations and relationships between species and environmental conditions. Each species occupies a localized habitat defined by different environmental characteristics. Antarctic krill are concentrated along the northwestern shelf break in a habitat characterized by deep (>1000 m) bottom depth, warm temperature (1 to 1.25°C), decreased sea ice, and proximity to the shelf break. Crystal krill and Antarctic silverfish are concentrated in Terra Nova Bay. Common characteristics of the habitat for these species are southwesterly location, coastal proximity, and cold temperature (−1.75 to −2°C). The habitat characteristics obtained for the 3 species provide a basis for projecting potential distribution changes in response to environmental change and for delineating regions of the Ross Sea for focused management and selection of marine protected areas that support ecosystem-level conservation plans.

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Antarctic krill (Euphausia superba) and crystal krill (Euphausia crystallorophias), important components of the Ross Sea food web, differ in their population distribution. The objective of this study was to determine whether these differing distributions result primarily from differences in spawning locations, larval development times, and transport by the Ross Sea circulation. To address this objective, Lagrangian particle tracking experiments were used to simulate the transport of larvae of Antarctic krill and crystal krill. The particle simulations showed that regions providing inputs of Antarctic krill to the Ross Sea were along the outer shelf/slope. Crystal krill transport and retention were along the shallow banks on the outer Ross Sea shelf. Particles initialized in the inner shelf off Victoria Land showed high retention in the region south and along the Terra Nova Bay polynya, with timescales consistent with development times of crystal krill. These results suggest that the cyclonic circulation over the shelf contributes significantly to the dispersion and retention of crystal krill in parts of the inner Ross Sea continental shelf that overlaps with regions with high concentrations of krilldependent top predators. The westward circulation along the shelf break contributes to the transport and aggregation of Antarctic krill in regions where Circumpolar Deep Water is observed on the outer continental shelf and along the shelf break. The transport pathways and connectivity obtained from this study provide a baseline for assessing the effects of projected changes in the Ross Sea circulation on the distribution of two important krill species.

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