The extensive growth of mariculture has been known to generate negative impact on the environment near mariculture cages. One of such negative impacts is organic enrichment. The magnitude of this impact depends on many factors: the type of fishes being cultivated; their feedings; density in the cages; topography of the site; sea bottom; and direction and strength of the water current.

Suggestions have been made to use artificial reefs as bio filtration for the excess of feeding remains from mariculture netpens. So far, four different localities have used artificial reefs in order to examine their effectiveness in terms of reduced impact from excess feeding remains. Those localities are in Israel, Hong Kong, Chile, and Spain. However, no research has been conducted in higher latitude region, or in a fjord environment.

In this research, two artificial reefs were built and deployed; one bellow mariculture netpen: artificial reef farm (ARF), and one in a control site 241 meters away: artificial reef control (ARC). In order to assess their biofiltration capability, 32 plates, made from the same material as the reefs' tubes, were attached to the reefs. In each sampling dive, that took place every two weeks during the research period, four plates were removed and examined in a laboratory. In addition, wild stock assessment was conducted by the divers.

Our results show that the reefs attracted both invertebrates, sessile and motile, as well as wild fishes. The succession of sessile species appeared from the fourth sampling dive and onwards. During the research, the presence of sessile species increased in number and in size. Motile species were also present in both reefs; their succession was early as they appeared by the first sampling dive. The number of motile species was greater in the farm site. Wild fishes were present only in the farm site, while hydrozoa was present only in the control site and grew extensively on the reef. Overall, biodiversity was greater at the farm site than the control site.

It can be concluded that the organisms found on the reefs, and the wild fish around it, showed the reefs' capability of being used as biofiltration as they succeeded to attract organisms that fed off the feeding surplus from the netpens. However, the full extent of their filtration capability is still to be determined.

KEY WORDS: Artificial reefs, biofiltration, organic enrichment, feeding remains