REPRODUCTIVE RESPONSE OF CALANUS-HELGOLANDICUS .2. IN-SITU INHIBITIONOF EMBRYONIC-DEVELOPMENT

Seasonal variations in the viability of Calanus helgolandicus eggs are reported in coastal waters off Roscoff, in the western English Channe l. In situ hatching success was highly variable with >50% amplitude be tween minimum and maximum values. Highest production of abnormal embry os and nauplii was recorded during spring and midsummer. Examination o f the faecal pellet contents produced by wild females revealed that th ey were feeding on extremely diversified prey, depending on the lime o f year. During spring-summer phytoplankton blooms, diatoms were always the dominant food, the remains of which were found in the faeces. Dur ing the rest of the year, non-diatom diets constituted the most import ant fraction of the prey. Inhibition of embryonic development was attr ibuted to the ingestion of diatoms by wild females, based on laborator y experiments demonstrating similar low hatching success and anomalies when females were fed dense diatom cultures. The failure to statistic ally establish a straightforward correlation between the concentration of chlorophyll a and variations of hatching success in the field is d iscussed with reference to experimental data.