Effects of increased habitat complexity on fish assemblages associated with large artificial reef units (French Mediterranean coast)

Large artificial reef units (LARUs; 158 m(3)) comprise 38% of 40 000 m(3) of artificial reefs deployed in France since 1985. Habitat complexity of one LARU was increased in situ in 1991 when 37 m(3) of small-sized building materials was placed randomly inside the empty chambers. The fish fauna, before and after added complexity, was compared with the fauna of an unmodified control LARD through 1987-1989 and 1997-1998, respectively, by visual censuses. The experimental LARU showed higher values of all community metrics investigated after treatment: total species richness had become twice as high, mean number of species per census 3 times higher, density 10 times, and biomass 40 times higher. Exceptionally large increases were observed among commercially important species such as sparids. In contrast, few changes were observed at the control unit: species richness had not changed significantly, while density and biomass showed moderate increases by a factor of 2-3, which might be explained by reef maturation. The results confirm the prominent role of habitat complexity in relation to artificial reef design on diversity and abundance of fish assemblages. (C) 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.