MEPS 314:227-238 (2006)  -  doi:10.3354/meps314227

ABSTRACT: In situ seasonal oscillations in female abundances, fecundity, egg-hatching success and survivorship of the first naupliar stage (N1) of the copepods Temora stylifera and Centropages typicus, collected from February 2000 to February 2001, were studied at a coastal station located in the Gulf of Naples (Mediterranean Sea). Adult T. stylifera and C. typicus females reached maximum abundances in different periods of the year, even though both species had similar breeding patterns with maximum egg-production rates (120 eggs female^–1 d^–1) in spring and early summer. Hatching success was generally >80%, showing weak seasonal trends in both species. In contrast, survivorship of N1 nauplii was much lower in T. stylifera (mean = 12%), compared to C. typicus (mean = 67%); on nearly 40% of the sampling dates, not a single N1 larva survived to moult to the second larval stage. On average, only 11 T. stylifera nauplii m^–3 d^–1 were recruited in situ over the year studied, compared to 139 C. typicus nauplii m^–3 d^–1. Only seasonal changes in egg- and pellet-production rates in both species were correlated with total integrated chlorophyll a (chl a), whereas hatching success and naupliar survival were not correlated with either chl a concentrations or with phytoplankton composition. Laboratory experiments showed that maternal feeding on Isochrysis galbana (ISO) or Prorocentrum minimum (PRO) for 7 d did not enhance naupliar survival in either copepod species, indicating that the negative effects of maternal diet did not disappear after feeding on a high quality food source. Naupliar survivorship was enhanced to >90% with the addition of a K algal culture medium to the natural phytoplankton assemblage, indicating that N1 nauplii were ‘drinking’ and absorbing dissolved material from the medium. Our results show that high hatching success in copepods can be followed by very low early larval survivorship and that the causes for low survival are not only related to maternal diet but also to the quality of the water in which the nauplii hatch. Scoring maternal and environmental effects on copepod recruitment rates should therefore also consider mortality of early naupliar stages.

KEY WORDS: Annual copepod cycle · Temora stylifera · Centropages typicus · Egg production · Hatching success · Naupliar survival · Maternal diet