Synergistic impacts of reduced grazing and nutrient enrichment on biofouling assemblages in a degraded coral reef ecosystem

While the coral reefs in the Persian Gulf have adapted to withstand some of the most challenging environmental conditions, overfishing and eutrophication can disrupt the structure of their associated biofouling assemblages. In the present study, the effects of reduced grazing pressure and eutrophication on the assemblage structure of biofouling functional groups in the coral reefs of Hengam Island (Persian Gulf) was investigated using a 21-month manipulative experiment utilizing settlement tiles. A total of 40 biofouling taxa were identified, none of which belonged to reef-building corals or the key facilitators of coral settlement. The effect of grazers on cover percentage was overshadowed by nutrient enrichment; suggesting a bottom-up control mechanism rather than top-down regulation in the coral ecosystem of the island. Our results suggest that grazers can reduce the coral-competing functional groups only in the absence of other confounding factors such as nutrient pollution • The interaction of nutrients and grazing on the recruitment of biofouling functional groups was investigated in the coral reefs of Hengam Island in the Persian Gulf. • In total, 40 biofouling taxa and subsequently 11 functional groups were identified; none of which belonged to reef-building corals or the key facilitators of coral settlement. • Our results suggest a bottom-up control mechanism rather than top-down regulation in the coral reefs of the island.