Multivariate analyses applied to Pleistocene bivalve assemblages from the Oga Peninsula (northern Japan) discriminate three distinct assemblages. The assemblages and their taphonomy were used to recognize environmental settings and changes. The Astarte–Cyclocardia–Glycymeris assemblage indicates shelf environment (below the storm wave base) where gravels and shells are transported from shallower settings. Supply of the exotic coarse sediment probably enabled epifaunal bivalves to inhabit the sea floor. The Glycymeris assemblage is characterized by dominance of G. yessoensis and represents current-swept shoreface environment (above the storm wave base). The Moerella assemblage is characterized by bivalves inhabiting bay to open-marine conditions and diverse deposit-feeders, indicating a moderately land-locked environment, such as an open bay or a bay mouth. Fine-grained substrata rich in organic matters in the bay were probably suitable for the deposit-feeders. Ordination also shows the assemblages along two environmental gradients, a bathymetrical one and the other related to open-marine and bay conditions. The environmental changes are explained mainly by glacio-eustatic sea-level changes and alternation of coastal geomorphology caused by local crustal movements. This study also suggests that fossil assemblages can be a powerful tool to reconstruct environments and depositional dynamics even in intensely bioturbated sedimentary facies.

Euphausiid life histories and distribution in the vicinity of South Georgia were studied from a series of samples taken in April 1980, November–December 1981, and July–August 1983. Size frequency data indicated a two-year life cycle for Euphausia frigida and the possibility of a three-year cycle for E. triacantha. The genus Thysanoessa was represented by a mixture of T. macrura and the dominant T. vicina. A one-year life cycle is proposed for the latter but that of the former is unknown. Spawning in E. frigida and to a lesser extent Thysanoessa spp. commenced as early as July and euphausiid calyptopes were a feature of the plankton for much of the year. E. superba eggs were found in low abundance over the shelf to the north of the island, but no hatched larvae were found. Behaviour patterns such as diurnal and seasonal migration partially confounded attempts to relate euphausiid distribution to environmental features. However calyptopes of most species, were generally more abundant in oceanic water deeper than 500 m and there was limited evidence that in August, E. frigida had commenced spawning in the colder part of the survey area.