MEPS 285:117-128 (2005)  -  doi:10.3354/meps285117

ABSTRACT: Egg production rate (EPR) and subsequent egg-hatching success of Temora longicornis from the southern Gulf of St. Lawrence were measured in the laboratory and at sea during 2 cruises in late June and early July of 2000 and 2001. A quantitative, functional Ivlev relationship between EPR, food concentration (µg C l^-1) and temperature was fit to the laboratory results. This relationship can serve as a template for expressing environmental control of T. longicornis egg production in models of the species population dynamics. Among the findings was a very low EPR at high temperature (18°C) when food was limiting (<200 µg C l^-1). The EPR of T. longicornis in the southern Gulf of St. Lawrence in early summer varied as a function of chlorophyll a concentration (integrated 0 to 50 m), and corresponded well with the functional laboratory relationship using a carbon/chlorophyll a conversion factor of 80. Mean hatching success in the laboratory was 42.8% for experimental temperatures <14°C, but declined dramatically to 7.5% at temperatures over 14°C. No relationship between hatching success and food concentration was observed. In the southern Gulf of St. Lawrence in late June, hatching success varied between 0 and 56% for mean temperatures between 3.3 and 10.9°C (median 6.6°C). While the presence of resting eggs at this time of year is the most probable explanation of our observations of low hatching success, other factors that may inhibit egg hatching, including methodology, insufficient fertilization and food quality, may also be implicated. We conclude that for T. longicornis, EPR is food-limited in early summer in this region. Comparison with other studies indicated that environmental controls on fecundity of T. longicornis may differ among regions where this species is the dominant copepod.

KEY WORDS: Copepod · Temora longicornis · Egg production rate · Hatching success · St. Lawrence