Ocean heat determines benthic trajectories on artificial as well as natural submarine substrata

Artificial substrata are common features in the inter- and shallow subtidal of the highly urbanized southern Persian/Arabian Gulf (PAG). Sometimes placed as artificial reefs, their benefits and integration into the local ecology often remain unclear. Temporal change in cover and composition of fauna/flora, focusing on corals, were investigated on the outer breakwater of Palm Jebel Ali (PJA; UAE), and 10 natural reefs in southern PAG from 2008 to 2024. The benthic community on PJA from 2008 to 2010 was characterized by bare rock, algal turfs and increasing cover by corals, bivalves and other invertebrates until 5 years after establishment in 2007, when it became coral-dominated. Coral cover declined from 2014 (PJA 68%; PAG reefs 40%) to 2024 (PJA 2%, PAG reefs 3%) and turf algae cover increased (2024: PJA 79%, PAG reefs 72%). Changes in bivalves and other invertebrates were subtle. Coral dominance on PJA changed from Porites spp. in 2008 to merulinid (Cyphastraea until 2014, then Platygyra). Acropora disappeared from 2015 on PJA and most PAG reefs. Heat exceeded the coral bleaching threshold in 2012, 2015, 2020 and the mortality threshold in 2017, 2018, 2021, 2023, 2024. Heat stress negatively correlated with coral survival (GLM) and community composition changed along the heat stress gradient (CCA) on both PJA and PAG reefs. Ocean heat caused similar community changes on artificial and natural substrata.