TIMING OF SPAWNING OF THYSANOESSA RASCHII (EUPHAUSIACEA) AND OCCURRENCE OF THEIR FEEDING-STAGE LARVAE IN AN ALASKAN BAY

Abstract

ABSTRACT The timing of spawning and onset of feeding for euphausiid larvae in Auke Bay, Alaska, was monitored for 3 years. Thysanoessa raschii was the most abundant euphausiid species in the study area. In all years the eggs were most abundant in the plankton soon after the major spring phytoplankton bloom was completed. During all 3 years of observation, the major cohort of stage I calyptopis, which is the first feeding stage, appeared in the plankton after the primary diatom bloom was finished. When the calyptopes initiated feeding, the water column was physically stratified and low nutrient availability limited primary production in the photic zone. The results suggest that euphausiid larvae in Auke Bay are dependent on secondary phytoplankton blooms for food, rather than the major spring diatom bloom. The concentrations of nauplii were about 70,000·m―2 in 1986, 40,000·m―2 in 1987, and 140,000·m―2 in 1988. Concentrations of calyptopes peaked at about 40,000·m―2 in 1986, 10,000·m―2 in 1987, and 70,000·m―2 in 1988. Maximum concentrations of furciliae were 730 to 1,660·m―2 in 1988, 1,037·m―2 in 1986, and 10 to 19·m―2 in 1987.