Life cycle, growth and reproduction of Neomysis americana in the St. Lawrence estuarine transition zone

摘要

Neomysis americana dominates the macrozooplankton of the St. Lawrence estuarine transition zone. Our aim was to determine how the growth and reproduction of N. americana may be controlled by environmental factors. The population was sampled fortnightly at Saint-Jean-Port-Joli from May to October 2013. A Bhattacharya cohort analysis was applied to the length-frequency data and the growth of each cohort was described by a von Bertalanffy function. Three cohorts were revealed. Slow growing females of the overwintering cohort produced the spring cohort in May. The summer cohort was released at the end of July producing juveniles of the new overwintering cohort in September and October. Two differential life history strategies were found: an overwintering cohort had an estimated longer life span (8-10 months), grew slowly, showed larger size at maturity and had a larger clutch size compared to those of the spring and summer cohorts. The clutch size was mainly influenced by female size and food quantity, unlike in many other studies, in which clutch size was found to be temperature dependant. These results concerning the life cycle, reproduction and growth of N. americana improve our understanding of the temporal dynamics of this important forage species of the St Lawrence estuarine transition zone.