An experimental approach to estimate egg production and development rate of the calanoid copepod Eurytemora affinis in Chesapeake Bay, USA
Résumé
The calanoid copepod Eurytemora affinis is the dominant copepod in Chesapeake Bay oligohaline regions and an important food source for larval fish, particularly during its early spring abundance peak. We measured life-history traits of E. affinis in cultures reared from Chesapeake Bay collections in food-saturated laboratory conditions at two temperatures (14° and 18 °C) and four salinities (1, 5, 15 and 21). We measured female life span, egg production, eggs produced over the life span, hatching success, mean clutch size, inter-clutch duration and nauplii survival. Adult females lived more than 2 months and produced more than 2500 eggs at 14 °C and salinity 5, with egg hatching success > 90%. Mean clutch size and inter-clutch time varied as a function of both temperature and adult senescence and ranged from 40 to 110 eggs clutch− 1 and 1.9 to 3.4 days, respectively. Egg production rate was also affected by adult senescence and averaged 37.8 eggs female− 1 day− 1 at 14 °C and salinity 5. Our results showed that E. affinis were adapted to cooler, fresher conditions more than the other dominant calanoid copepod in the Chesapeake Bay, Acartia tonsa, which has been shown to be well adapted to warmer temperatures and higher salinities. E. affinis exhibited better survival, development rate and naupliar production in lower temperatures and salinities compared to A. tonsa. At higher temperatures and salinities, E. affinis repeatedly released egg sacs with unhatched eggs prior to extrusion of a new egg sac. The dropped egg sacs contained eggs that were not yet hatched, a condition not observed in other species in the genus Eurytemora and which may indicate a potential cost of carrying eggs at higher temperatures.