Enrichment of aquaculture earthen ponds with Hediste diversicolor: Consequences for benthic dynamics and natural productivity

The present work analysed the potential impacts of the enrichment of semi-intensive production earthen ponds with the ragworm Hediste diversicolor in the benthic dynamics and natural productivity. The macrobenthos and sediment characteristics were analysed in two enriched ponds and two control ponds in May, June and September 2005. The number of species, Margalef species richness and biomass (AFDW) were generally significantly higher in enriched than in control ponds, while for abundance no clear pattern was visible. Multivariate analysis showed differences in macrobenthic community structure of control and enriched ponds. Differences were also visible when the introduced species was removed from the data set, indicating that differences were mainly due to changes in other species abundance. In general, gastropods (Akera bullata, Jujubinus striatus, Hydrobia ulvae, Rissoidae), bivalves (Abra ovata, Cerastoderma spp.), crustaceans (Ampithoe rubricata, Dexamine spinosa, Gammarus insensibilis, Gammarella fucicola, Iphinoe tenella), and also some polychaetes (Desdemona ornata, Terebella spp., Syllis gracilis and Neanthes caudata) greatly increased their abundances in enriched ponds. On the other hand, the abundance of Tubificidae, Capitella spp., Pseudopolydora paucibranchiata, Corophium acherusicum, and Mesopodopsis slabberi decreased. The organic matter content was significantly lower in enriched ponds, probably due to the positive impact of the polychaetes on sediment reworking, resulting in higher organic matter mineralization. Overall the present study indicates that stocking of earthen production ponds with H. diversicolor significantly altered community structure of benthic invertebrates and may improve environmental conditions for fish production by reducing the organic matter accumulation in pond sediments.