DISTRIBUTION AND DIEL VERTICAL MIGRATION OF THE EUPHAUSIID THYSANOESSA-MACRURA IN GERLACHE STRAIT, ANTARCTICA

Thysanoessa macrura was found throughout Gerlache Strait, Antarctica, during four surveys carried out from 30 October to 23 November 1989, w ith the highest abundance being 332 individuals m-2 (0-290 m). Reprodu ction had begun just before the surveys took place, as indicated by th e presence of females with attached spermatophores and of larvae. Thir teen-month old females were reproductive. Larvae in 9 depth strata bet ween 0-290 m were dominated by calyptopis stages, and developed from c alyptopis 1 to furcilia 1 during November. Larval abundance was not co rrelated to chlorophyll a concentration, which showed a consistent eas t-west gradient in Gerlache Strait with highest concentrations (>30 mg chlorophyll a m-3) in bays of the Antarctic Peninsula. Survival of la rvae appeared to not be affected by phytoplankton abundance. Older T. macrura showed strong diel vertical migration between the surface at n ight and depths to 120 m during mid-day. Larvae were consistently foun d iii the chlorophyll a-rich upper 50 m during night (90%) and day (81 %), while adults and juveniles were found in the upper 50 m at night ( 83%), but only 16% remained there during the day.