Functional traits unravel temporal changes in fish biomass production on artificial reefs

Abstract : reefs (ARs) are deployed worldwide as they are expected to support fisheries management. 22 While the underlying mechanisms remain widely debated, production was recently determined as 23 the most probable cause of increases in fish biomass. Changes in fish biomass in a temperate AR 24 system were investigated from December 2008 to November 2015 by considering seven distinct 25 functional groups, and isotopic functional indices were used to identify how these changes may have 26 affected organic matter (OM) fluxes. Contrasting patterns of change were observed between 27 functional trophic groups, highlighting that combining the biomass of all species present in a 28 community is inappropriate for assessing AR-induced effects. Benthic sedentary species 29 predominated (>75% of the total biomass) through massive production, with a 68-fold increase in 30 mean biomass over the study period. Mobile species tended to vary seasonally, suggesting only a 31 slight influence of AR. Zooplanktivores biomass decreased over the 6-year period, as a possible result 32 of changes in environmental conditions. Isotopic indices helped to reveal both the community 33 maturation and the importance of local OM sources not only in supporting fish biomass production 34 but also in attracting pelagic species. Our results corroborate that production and attraction are two 35 extremes of a range of contrasting patterns and highlight the importance of considering the specific 36 responses of functional components of fish communities to accurately describe changes in AR 37 functioning. Functional attributes such as trophic traits, habitat use and dispersal abilities must not 38 be overlooked as they modulate fish species responses to the deployment of man-made rocky 39 substrates.