Succession of benthos settled on freshwater Artificial reefs in Sari

Density and succession of benthic invertebrate of four Artificial Reefs (cemented rope, brick, wood, ceramic) were studied. The samples were collected every fifteen days form March till September 2004. Sampling was done in the sedimentation pool in Ecological Research Center of Caspian Sea, Sari, Iran. A total of 2,901 benthic individuals per m2 of six species were collected that include two species of bivalves, three species of gastropods and one species of crustacean. The biomass of benthos was measured as wet weight. The Total benthos biomass was 975.636 gr/m2. Also the temperature was measured and its relationship with the density and biomass of invertebrate was analyzed.Considering the succession of benthos, first the two algal species of Chara sp. and Nitella sp. appeared on Artificial Reefs; then, the gastropod Psuedomnicola sphaerion and finally, bivalves Dreissena polymorpha and Cerastoderma lamarckii. The gastropod Valvata piscinalis appeared later. After that, the gastropod Planorbis contortus and finally the shrimp Palaemon elegans were found on artificial reefs. D. polymorpha showed the densest population on reefs with a density of 593.108 gr/m2. Results also showed that brick and ceramic treatments attracted more benthic animals (P<0.01). Cemented rope was next and wood was the last in number and biomass of the benthos (P<0.01). The Presence of fish (Carassius carassius) and frog (Rana rana) species around the artificial reefs showed that artificial reefs produce food for the bigger predators.