A multi-species assessment of artificial reefs as ecological traps

Abstract

All of the marine environments have been found to be affected by anthropogenic impacts with the sprawl of marine infrastructure being one of the most extreme factors modifying habitats. Artificial reefs (ARs) are a common type of these infrastructures, that are frequently used for fisheries management, species conservation and habitat restoration. Attractiveness of ARs for some species have been demonstrated, however little is known about the fitness of individuals that occupy ARs compared to natural reefs. ARs that provide lower fitness advantages may become ecological traps. We examined individual fitness of three species (Trachinops caudimaculatus, Vincentia conspersa and Trinorfolkia clarkei) occupying three different habitat types: natural reefs, Reef Ball reefs (RBs) and custom-designed artificial reefs (CDARs) in Port Phillip Bay, Victoria, Australia, through comparing a range of condition indices (hepato-somatic, gonado-somatic and relative weight index). Additionally, we investigated mortality rates of new recruits and juveniles of T. caudimaculatus among habitat types. T. caudimaculatus exhibited nine times higher instantaneous mortality rates on RBs than the other two habitat types. Combined with known habitat preference of T. caudimaculatus for RB, this suggests that RBs may act as an ecological trap for this species. V. conspersa exhibited higher fitness on RBs, while T. clarkei fitness proxies were context dependent. Although our results indicate that responses by fishes to artificial habitats are species-, location- and habitat-specific, this is one of the first studies to demonstrate the formation of ecological traps in the marine environment due to proliferation of artificial reefs.Poorly designed or placed ARs may lead to insufficient positive outcomes or even significant negative impacts on marine communities. Combined with high costs, these effects may lead to reduced social acceptance of new placements and could impede future management and conservation efforts.