Artificial aquatic habitats: a systematic literature review and new perspectives

Anthropic structures have been deployed in aquatic environments for the most variable purposes. Here, we review the use of artificial aquatic habitats (AAHs) worldwide through a systematic and comprehensive search of peer-reviewed literature. We aimed to synthesize the knowledge on the subject, identify gaps, and propose new perspectives for future research. In total, 460 peer-reviewed papers from 1972 to mid-2016 were included in our systematic review. Field studies carried out in marine temperate environments were predominant, whereas fewer efforts have been made in marine tropical and freshwater ecosystems. Experimental habitats made of concrete were the most common artificial structures. Visual census was the most used sampling method, and there was a dominance of short-term (< 12 months) and shallow waters (< 5 m depth) studies. Fish was the most studied group (18%), whereas tunicates encompassed the large proportion of non-native species associated with AAHs (32.9%). Although idealized for the promotion of biodiversity, AAHs have been serving as stepping stones for non-native invasive species, facilitating biotic homogenization by increasing the connectivity of hard-bottom systems. The scarcity of studies in coastal tropical and freshwater ecosystems, as well as the efforts with reduced temporal scales and restricted depths, calls for future research to better understand the role of artificial habitats, especially in climate change scenarios. In this sense, we provide a conceptual framework exploring major issues regarding AAHs, including biodiversity status, ecosystem services, and climate change, in order to guide future research and assist conservation measures.