Influence of an artificial reef on soft bottom macrofauna

Abstract

The present study, carried out off the northeastern coast of Malta, was aimed at establishing the influence of artificial reefs on the sandy bottom macroinvertebrate assemblages in their vicinity. The objectives were to assess to what distance from the reefs such influence, if any, extends, and whether reefs constructed from different materials have the same effects on the benthic habitat. Two replicate artificial reefs, one consisting of blocks made of a Globigerina-based concrete and the other of identically shaped Globigerina-limestone blocks, were deployed in September 2004 at a depth of ca. 40 m. Sediment samples were collected prior to deployment of the reefs and following deployment, in order to assess changes in physical parameters, including grain-size and organic carbon content, and to study the infauna at the two artificial reef sites and at two ‘bare sand’ reference sites. The results indicated that deployment of the artificial reefs led to a change in the sandy bottom biotic assemblages; however, the observed effects were limited to the area in the immediate vicinity (1 m – 2 m) of the structures. Such effects were possibly brought about by changes to the physical and biological characteristics of the sand habitat principally resulting from scouring around the structures and from modification by reef-associated organisms, accumulation of seagrass debris, which increased the organic content of sediments, and increased predation by vagile fauna that colonised the reefs. Overall, the influence of the artificial reefs on the adjacent bare sand habitat and associated assemblages was minimal.