Changes in the composition and structure of soft bottom macrobenthic assemblages brought about by the deployment of an artificial reef

Abstract

Two replicate sets of artificial reefs, one consisting of blocks made of a Globigerina based concrete and the other of identical Globigerina-limestone blocks, were deployed on a sandy bottom bare of vegetation off the Sliema-St Julians area, in 40 metres of water, during September 2004. This was done as part of an 'Artificial Reef Project', whose key aims are to study the impact of the artificial reefs on the surrounding environment, the colonization of the reefs, and the suitability of their component materials for reef construction, in order to provide scientific data for the formulation of a national artificial reefs policy. The objectives of the present study were to investigate if the artificial reefs have any effects on the sandy bottom biotic assemblages at their deployment site, how far from the reefs these effects extend, and if reefs constructed from different materials have the same impact. To investigate this, physical parameters (grain-size and organic carbon content) and biota of the sandy bottom surrounding one set of replicate reefs were compared with two 'bare sand' control sites using a 'Before-After' experimental protocol. Sediment samples were collected pre-deployment, between December 2003-February 2004, and post-deployment, between February 2005-April 2005, along two 50m-long transects located to the west and east of each reef deployment site; samples were also collected from the sand control sites.