Can wrecks serve as exploitable surrogate habitats for degraded natural reefs?

Overfishing is a key stressor in many coral reefs, affecting their function and ecosystem services. In the Gulf of California, 50 years of artisanal and recreational fishing have removed most of the largest and most vulnerable fish species, the Espiritu Santo Archipelago (ESA) is a marine protected area (MPA) where artisanal and recreational fishing are allowed in most of the natural reefs, while the artificial reefs (wrecks) are fully protected. An important question under such circumstances is whether artificial reefs can serve as surrogate habitats for the natural reefs. To address this question, we characterized the fish community (species richness, abundance, differences in taxonomic structure) and analyzed the obtained data by multivariate ordination and similarity analysis. The highest species richness was found in the artificial reefs, with total of 83 species, of which 21 species were exclusive. Contrary to the species richness, the total fish abundance was 20% higher at the natural reefs. The fish assemblages of the artificial reefs differ significantly from those of the natural reefs. The natural reefs of the ESA are dominated by few fish species from families of lower trophic levels. In contrast, the studied shipwrecks provide refuge to commercially important fish species (such as Snappers, Triggerfish, Jacks, and Groupers) including threatened species. The different fish compositions on the natural and artificial reefs is likely to be the outcome of differential fishing pressure. The non-fished areas (wrecks) of the ESA may represent a good strategy for reef restoration, enhanced fishing grounds (via spillover) and fishing management. However, the fish community structure of the artificial reefs differs from natural rocky reefs of the ESA, and therefore, should not be considered as surrogate habitats for natural reefs. The results point out the need to reassess the management effectiveness of the natural reefs of the ESA.