The scyphomedusan fauna of the Japan Trench: Preliminary results from a remotely-operated vehicle

Abstract

A series of dives was conducted during April/May 2002 in a variety of water masses over the Japan Trench using the remotely-operated vehicle ROV HyperDolphin. The scyphomedusan fauna was catalogued, resulting in the first records of Atolla vanhoeffeni and Atolla russelli from Japanese waters. A new genus and species referable to the family Paraphyllinidae was also recognized. The ulmarid scyphomedusa Poralia rufescens is by far the most common scyphomedusa in these waters. Its distribution was determined by water mass structure and it was not present in subducted Oyashio Current-derived waters occurring within its usual depth range. Temperature and salinity affected its distribution more than dissolved oxygen concentrations. Distributional information, data on the physico-chemical parameters of the water column, and notes on biological associations with scyphomedusae are introduced.