Temporal changes in the genetic structure of intertidal populations of Hediste diversicolor (Polychaeta: Nereididae)

In order to assess the occurrence of temporal variations in the genetic structure of populations of Hediste diversicolor, four intertidal sites (10 m2 wide) located in two estuaries of the Adriatic and Tyrrhenian coasts of Italy (Pialassa and Serchio) were repeatedly sampled from 2001 to 2003. Temporal genetic changes were investigated at six allozyme loci (ALD, FH, HBDH, LDH, PGI and SDH). Allelic frequencies, percentages of polymorphic loci, mean observed and expected heterozygosities varied both between sampling times and among sites. At each site, FST values revealed significant temporal changes between sampling times. The observed temporal genetic variability along with patterns of genetic fragmentation previously described suggests the occurrence of ‘chaotic genetic patchiness’ within estuaries. Results support the model proposed by Authors who, analysing population dynamics and secondary production of H. diversicolor, hypothesised that densities of H. diversicolor are primarily affected by periodical mortality events followed by recruitment peaks. Genetic drift, related to mortality events, and/or sweepstake reproductive success, with a small number of individuals responsible for the recruitment within patches, appear to be major processes promoting the genetic structuring of H. diversicolor within estuaries.