Comparing the reproductive success of three Palaemonid species in a Mediterranean coastal lagoon: native and invasive responses to salinity changes

Salinity changes in transitional water ecosystems are a natural feature, but anthropogenic direct or indirect impacts are drastically altering their equilibrium and, therefore, their biological communities. Females of three species of Palaemonidae shrimps (the invasive Palaemon macrodactylus and the native P. adspersus and P. elegans) were collected in nature and kept in laboratory at salinities 20 and 30. For each species, the reproductive strategy (investment devoted to reproduction) and the reproductive performance (larval output and hatching success) were determined. Significant differences were observed comparing the three species, highlighting an opportunistic r-strategy in P. macrodactylus and P. elegans, while P. adspersus resulted to produce fewer and larger eggs. Palaemon elegans showed a lower hatching success than the other two species, and the size-adjusted larval output appeared to be highly sensitive to salinity variations, with a strong increase under euhaline conditions (salinity 30), while this increase was limited in the other two species. The selected species were used as model organisms to understand which could be the shift in biological communities due to salinity variations. Data suggest that a shift towards euhaline conditions will favor the native populations, while a shift towards mesohaline waters could determine an increase of the invasive shrimps.