Ecology of idotea-baltica (pallas) populations in the lagoon of venice

A two-year study was carried out on the ecology and dynamics of two Populations of Idotea baltica from the lagoon of Venice. Body size variations were found to follow a seasonal pattern at Romea, the sampling station located in the central part of the lagoon, but not at Toro, the marginal area. The reproductive period extends throughout the year, but the frequency of ovigerous females and the number of eggs in the marsupium are seasonally variable, achieving the maximum in summer. A significant correlation between number of eggs and body size of the female was found. The examined population variables were not affected by the colour morph. Frequency fluctuations of the major colour phenotypes (uniformis and bilineata) were quite variable at the Toro station, and apparently regular at Romea. The differences in the behaviour of a number of biological variables were not due to genetic factors or to salinity and temperature, which are very similar in the two stations. Instead they probably depend on the demographic changes caused by migratory behaviour of the species, and on the different levels of current speed in the two sampling areas.