An Ecological Investigation on Colonization of Fresh Water Artificial Reefs

Colonization of four different artificial reefs (cemented rope, brick, wood and ceramic) was studied during a six-month period. The study was conducted in a fresh water pond filled with water from the Tajan River, a river in north Iran which flows into the Caspian Sea. A total of 2901 benthic individuals were collected in a biweekly sampling program. Eight species colonized the reefs including two bivalves, three gastropods, one prawn and two algae. The two algal species, Chara sp.and Nitella sp. were the first settlers on the freshwater artificial reefs in late April and May 2004. Within one month the gastropod Psuedomnicola sphaerion and the bivalves Dreissena polymorpha and Cerastoderma lamarckii were also settled. The gastropods Valvata piscinalis and Planorbis contortus appeared in July with two weeks difference. The prawn Palaemon elegans was found taking refuge in ceramic vase treatments in late August and early September. Biomass was assessed for wet weight and totalled 975 g/m2. D. polymorpha at 593 g/m2 was densest settler on reefs. Colonization was faster and denser on brick and ceramic. Cemented rope was next, and wood was last. Observation of fish (Carassius carassius) and frog (Rana rana) around artificial reefs provided evidence that these reefs are producing food, as benthic animals, for the predators of the pond. Water temperature was measured and its effect on colonization is discussed.