Population structure and life history of Hemimysis lamornae mediterranea (Malacostraca: Mysida) in the Ebro Delta (NW Mediterranean)

Hemimysis lamornae mediterranea Bacescu, 1936 has been recently reported in the Ebro Delta (Spain, NW Mediterranean). Little is known about the biology and ecology of this mysid and we provide the first information about its population biology. H. l. mediterranea were collected from Sant Carles de la Ràpita harbor from June 2010 to March 2012 at night. The H. l. mediterranea population was composed of two main individual size categories: larger-sized winter/spring individuals and smaller-sized spring/summer individuals. The overall sex ratio is highly skewed; mature females are 2.5 times more abundant than mature males. Reproductive activity was higher during late winter and spring but was almost continuous throughout the year. The intra-marsupial development and growth of juveniles has been studied in the laboratory. The mean duration of incubation period (intra-marsupial stages) in laboratory conditions was 11 days (20 °C) and the age at first maturity ranged from14 to 20 days. The growth rate was faster in early juveniles and declined with age, showing a maximum of 0.152 mm d− 1. The laboratory results and demographic data suggest that H. l. mediterranea will produce several generations per year in the Ebro Delta. H. l. mediterranea was characterized by a combination of early maturation of individuals (short juvenile period), rapid growth, small adult size, a continuous reproduction all year round, iteroparous females, a relatively high fecundity and a high number of generations per year.