The effects of temperature and salinity on egg production and hatching success of Baltic Acartia tonsa (Copepoda: Calanoida):: a laboratory investigation

The functional response of the aspects of reproductive success of a southwestern Baltic population of Acartia tonsa (Copepoda: Calanoida) was quantified in the laboratory using wide ranges in temperatures and salinities. Specifically, daily egg production (EP, # female(-1) day(-1)) was determined for 4 or 5 days at 18 different temperatures between 5 and 34 degrees C and the time course and success of hatching were evaluated at 10 different temperatures between 5 and 23 degrees C. The effect of salinity (0 to 34 psu) on egg hatching success was also examined. The highest mean rates of EP were observed between 22 and 23 degrees C (46.8-50.9 eggs female(-1) day(-1)). When studied at 18 psu, hatching success of eggs increased with increasing temperature and was highest (92.2%) at 23 degrees C. No hatching was observed for eggs incubated at low temperatures (<= 12 degrees C) that were produced by females acclimated to temperatures <= 10 degrees C indicating a possible thermal threshold between 10.0 and 13.0 degrees C below which only the production of diapause (or low quality) eggs exists in this population. When tested at 18 degrees C, the hatching success of eggs incubated at 15 different salinities increased asymptotically with increasing salinity and was maximal (81.4-84.5%) between 17 and 25 psu. The high reproductive success observed over wide ranges in temperatures and salinities in this Baltic population demonstrates one of the mechanisms responsible for the cosmopolitan distribution of this species within productive, estuarine and marine habitats.