Population structure and life history of Siriella jaltensis (Crustacea: Mysida) in the Ebre Delta (NW Mediterranean)

This work is focused on the study of some aspects of the population structure and reproductive biology of the mysida Siriella jaltensis in the Ebre Delta, Western Mediterranean. The samples were collected monthly in Sant Carles de la Ràpita Harbor between June 2010 and March. The S. jaltensi s population comprised two main individual size categories: large winter individuals and small summer individuals. The sex ratio (number of females / number of males), as calculated from the complete data set, was not significantly different from 1. However, the sex ratio fluctuated throughout the sampling period. Demographic data suggest that S. jaltensi s produces several generations per year in the Ebre Delta which it is characterized by a combination of early individual maturation (in spring and summer), continuous reproduction all year round, iteroparous females and relatively high fecundity (mainly during late spring and summer). The number of eggs per female was related to size, as well as the number of nauplioids and postnauplioids. The volume of the eggs was also related to the size of the females. The egg size of medium-sized females, who are present in summer and winter, is related to the temperature. Larger eggs, in winter, produce larger juveniles which are probably more resistant. This is a strategy commonly used by species of peracarids in ecosystems in which the mortality is greater in the early juvenile stages.