ORIGINAL ARTICLE Fish assemblages and rapid colonization after enlargement of an artificial reef off the Algarve coast (Southern Portugal) Francisco Leita ˜o 1 , Miguel N. Santos 1 , Karim Erzini 2 & Carlos C. Monteiro 1 1 IPIMAR, Olha ˜ o, Portugal 2 Centro de Cie ˆ ncias do Mar (CCMAR), Universidade do Algarve, Faro, Portugal Problem Artificial reefs (ARs) have multiple purposes, including the enhancement of fishery resources and the rehabilita- tion ⁄ mitigation of habitat loss (Bohnsack & Sutherland 1985; Monteiro & Santos 2000; Ramos-Espla ´ et al. 2000). In the Algarve, on the Southern Portuguese coast, an AR program aiming at the sustainability of local nearshore fisheries has been established since 1990. The Algarve ARs have been shown to have an impor- tant role, serving as protection areas for juveniles that migrate from surrounding nursery areas (Santos et al. Keywords Algarve (Portugal); artificial reefs; biomass; colonization; composition; fish assemblages; recruitment; seasonality; similarity. Correspondence Francisco Leita ˜ o, IPIMAR, Avenida 5 de Outubro s ⁄ n, 8700-305 Olha ˜ o, Portugal. E-mail: fleitao@cripsul.ipimar.pt Accepted: 3 May 2008 doi:10.1111/j.1439-0485.2008.00253.x Abstract Artificial reefs (ARs) have been deployed in Algarve (Southern Portugal) coastal waters to contribute to the sustainability of local nearshore fisheries. Herein, we describe the colonization process of the recently deployed Faro ⁄ Anca ˜o AR, and assess the time until the fish assemblage reaches stability and their seasonal patterns. In addition, we compare the results from the present study with those previously reported for an older AR. The fish assemblages were monitored monthly over a 2-year period by means of visual census. A rapid increase in fish colonization occurred within the first 4 months. After this initial period the assemblage structure showed high similarity (> 73%). The high rate of col- onization of the AR was related to the maturity already achieved by the nearby 14-year-old AR and to the fish migration from the Ria Formosa lagoon, a nearby nursery habitat. The reef fish assemblage structure showed a seasonal pattern, mainly associated with recruitment episodes of occasional demersal species (Boops boops, Trachurus trachurus and Pagellus spp.) in spring and sum- mer. A total of 66% of the species found in AR are of commercial and recrea- tional importance. The overall mean density and biomass were 2.8 indÆm )3 and 207 gÆm )3 . The occasional demersal species accounted for 42% of the fish den- sity. The most important species in terms of biomass belong to the Sparidae family along with Dicentrarchus labrax. The fish assemblage of the new ARs showed higher mean number of species, diversity, density and biomass values than those reported for the older AR. This result was associated with enlarge- ment of the AR area and with the fishing exploitation of the isolated, small and patchy old AR. Moreover, the high biomass values recorded in the new ARs were mainly due to the increased density of D. labrax after AR enlarge- ment. The results of the present study are used to define guidelines for suitable management strategies for the AR areas that are exploited by the local com- mercial and recreational fisheries. Marine Ecology. ISSN 0173-9565 Marine Ecology 29 (2008) 435–448 ª 2008 The Authors. Journal compilation ª 2008 Blackwell Publishing Ltd 435