Centenary shipwrecks reveal the limits of artificial habitats in protecting regional reef fish diversity

Abstract

1. The sinking of artificial structures has become increasingly common around the world, but whether the artificial structures favour or disfavour fish diversity remain under debate. Sinking may empty the nearby natural reefs locally and regionally by attracting their biota. Conversely, it may improve environmental conditions for species survival and reproduction, acting as source of diversity at the local and regional levels.2. We tested these contrasting hypotheses by assessing the taxonomic, functional and phylogenetic diversity of 12 fish communities in Northeast Brazil: four ageing (>100-year-old) shipwrecks and eight surrounding natural reefs at comparable depths and distances. We partitioned the gamma diversity of artificial and natural reef communities into independent alpha and beta components, accounted for species' abundance and assessed whether beta patterns were mostly driven by spatial turnover or nestedness.3. We recorded 6,335 individuals distributed in 88 fish species and 38 families. While artificial and natural reefs shared 50 species (57%), 21 species (24%) were exclusive to the artificial reefs, suggesting that the nearby natural reefs-the most likely original source of these exclusive species-do not harbour them anymore. Alpha diversity of typical and dominant species did not significantly differ between the reef types, but alpha diversity of rare species was taxonomically, functionally and phylogenetically higher in artificial reefs, indicating positive effects of the structures at the local scale. 4. By contrast, regional beta diversity was higher in natural reefs in terms of taxonomic and functional diversity, regardless of species abundance. Pairwise beta diversity indicated that turnover had a large effect on the compositional dissimilarity in both reef types, whereas nestedness was almost irrelevant in artificial reefs. Synthesis and applications.Artificial structures such as shipwrecks may promote the co-occurrence of rare species, but they are unable to produce the beta diversity patterns that natural reefs do, even following many decades of colonization.Although artificial habitats host a significant portion of the regional reef fish diversity, they may have also contributed to the degradation of nearby natural reefs.

No effect of nearby natural reef existence on fish assemblages at shipwrecks in the Aegean Sea

“…loss of herbivores to ARs as a result of food-web alterations; Fowler & Booth, 2012) effects of artificial reefs were reported on the structure and function of communities on nearby natural reefs. Consistent with these effects, Medeiros et al (2021) suggested that artificial structures contributed to the degradation of fish diversity in their natural environment. These findings stress the importance of reef site selection.…”

“…Consistent with these effects, Medeiros et al . (2021) suggested that artificial structures contributed to the degradation of fish diversity in their natural environment. These findings stress the importance of reef site selection.…”

“…These findings stress the importance of reef site selection. The placement of the artificial reefs should be done with caution in order to conserve and restore the natural reefs and their surrounding aquatic environment (Sheng, 2000), they should not be deployed close to natural reefs or rocky habitats (Medeiros et al ., 2021). In our study area, the shipwrecks Alaybey (100 m to rocky habitat of Büyükada Island) and 9 Eylül (15 m to rocky habitat of Küçükada Island) were sunk to the locations without any comprehensive analysis to assess potential impacts on the biota of the natural reefs.…”

Prevalence and extent of coral diseases in shallow and mesophotic reefs of the Southwestern Atlantic

“…This geographic isolation may have precluded gene flow across the shelf and eventually influenced the greater resistance in shallow areas (Weil 2019; Bloomberg and Holstein 2021), but further studies on innate immunity against disease are needed to properly assess this hypothesis. The proximity with the Paraiba coast has also put the shallow colonies in contact with several anthropogenic disturbances over the past five centuries (e.g., pollution, overfishing, mass tourism, sinking of artificial structures; Medeiros et al 2022), which together changed water quality and sedimentation for corals, their symbionts and pathogens. However, according to our findings, these nearshore abiotic changes were not enough to increase the prevalence and extent of diseases.…”

Theory, practice, and design criteria for utilizing artificial reefs to increase production of marine fishes

“…Studies comparing fish assemblages on shipwrecks (i.e., high-relief artificial reefs) with natural reefs and/or concrete artificial reefs found higher-relief wrecks have higher mean densities of fishes pattern. Yet, shipwrecks were not necessarily adequate surrogates for natural reefs (Medeiros et al, 2021). This is representative of a general pattern of predators being more common on artificial reefs globally, with transient predators being observed in higher densities on taller structures (Paxton et al, 2020a).…”