Influence of the artificial reef size configuration on transient ichthyofauna – Southeastern Brazil

• We assessed the size effect of small-scale artificial modules on transient fish.
• We associated this effect with the reef's area of influence on its surroundings.
• Larger modules had a decrease in richness and abundance per standardized volume unit.
• Reefs of 1 m³ are recommended for transient fishes, such as Ariidae and Sciaenidae.
• The local seasonal fluvial influence may outweigh the reef configuration effects.

To investigate how variations in the volume of artificial reefs affect the structure and composition of the transient ichthyofauna, reefball-type concrete modules were arranged at 9 m of depth along the northern coast of the state of Rio de Janeiro. The modules were arranged in three configurations, each in triplicate: (1) solitary modules (1 m3), (2) side-by-side modules (2 m3) and (3) modules forming a triangle (3 m3). The surrounding ichthyofauna were sampled in two periods of the year (dry: September 2009 and October 2010; rainy: April 2010 and April 2011) with gillnets to record the richness, species diversity, number of individuals and biomass per volume unit. The total mean values of richness, diversity, number of individuals and biomass did not differ significantly among the reef volumes. However, when these variables were analyzed per standardized volume unit, there was an increase in these variables with the increase in reef volume, considering all the transient ichthyofauna as well as the most representative families, Ariidae and Sciaenidae. A non-metric multidimensional scaling ordination analysis revealed differences in the composition of the ichthyofauna between the sampling periods, dominated by Sciaenidae (Stellifer rastrifer, Paralonchurus brasiliensis, Larimus breviceps and Cynoscion virescens) in the dry period and by Ariidae (Aspistor luniscutis) and Carcharinidae (Rhizoprionodon porosus) in the rainy period. The results suggest that the increase in module size from 1 to 3 m3 may result in slight alterations in the community descriptors, with a decrease in the relative values of richness, diversity and density per standardized volume unit. Furthermore, the effects of the seasonal flow of the Paraíba do Sul River may overlap the effects of reef configuration, mainly in the rainy period with higher flow. The implementation of several dispersed 1 m3 modules seems to be the most favorable configuration to attract transient ichthyofauna, especially Ariidae and Sciaenidae, on the northern coast of the state of Rio de Janeiro.