Temperature effects on Calanus helgolandicus (Copepoda: Calanoida) development time and egg production

Abstract

Effects of temperature on aspects of the life cycle and physiology of the copepod Calanus helgolandicus (C. helgolandicus) were investigated in the laboratory. Development times (DTs) were determined for organisms reared individually at 9, 12 and 158C under saturated food conditions. While animals were successfully reared from egg to adulthood at 12 and 158C, at 98C, all the individuals had died prior to entering NV. The cohorts were fed with a monoculture of Prorocentrum micans as food saturating conditions. The cohorts were fed with monocultures of Prorocentrum micans which should represent saturated food concentrations with a dinoflagellate diet used in many other experimental studies. However, the monoculture nature of the diet and/or the laboratory containment conditions may have caused the mortality rates encountered. Impacts of shortterm temperature change on egg production (EP) and hatching success were also investigated over the course of 1 year on individuals collected from station L4 (Western English Channel) and incubated in the laboratory. DTs increased as temperature decreased, with longer DTs at comparable temperature with those in Thompson’s study [(1982) Growth and development of Pseudocalanus elongatus and Calanus sp. in the laboratory. J. Mar. Biol. Ass. UK, 62, 359‐372.] Evidence is presented to suggest that in this other study a mix of Calanus finmarchicus and C. helgolandicus may have been used. Equiproportional development was observed for the nauplii, but no pattern was defined for the copepodites. At low temperatures, mortality rates in the incubations were higher, but adult condition factor was higher, the longer DTs allowed greater body mass to be accumulated. EP rate was correlated with temperature at station L4, but the short-term incubation temperature did not have a significant influence on EP when measured over a short timescale (24 h). Egg hatching success also did not differ between incubations with small temperature differences.