Egg production and hatching success in the peri-Antarctic copepod Calanus simillimus

In situ rates of egg production and hatching success are reported for Ca[an us simillimus, one of the most abundant calanoid species in peri-Antarctic regions, during the Italian 'Italica' cruise in the Straits of Magellan in March-April 1995. Low fecundity (8.6 eggs female(-1) day(-1)) and fecal pel let production (0.8 fecal pellets female(-1) day(-1)) in this period indica te that the species was feeding very poorly. Sixty-six of the 126 females s ampled did not produce eggs and 80 of these did not produce any fecal pelle ts during the 24 h period of incubation. Striking abnormal naupliar and emb ryonic development was recorded in 81.8% of the eggs spawned. Aberrant eggs did not undergo normal cleavage, and failed to develop to hatching. Deform ed nauplii were asymmetrical and presented strong anatomical anomalies in t he total body length and number of swimming appendages. These results are d iscussed in the light of recent findings on the causes of low hatching succ ess in copepods.