Temporal shifts in algal and fish assemblages following the introduction of herbivorous species in coral reef patches (Bora Bora Island)

Abstract

Ecological succession (sequential replacement of species following a disruptive event) is critical for understanding ecosystem dynamics. With coral reefs facing increasing threats, comprehending secondary ecological succession is of heightened importance. Coral reef restoration, through techniques such as coral transplantation and herbivore introduction, plays a crucial role in mitigating coral degradation at the local scale. However, the combined effect of these two techniques on ecological succession remains understudied. To determine the impact of herbivory and coral transplantation on ecological succession, four experimental conditions were evaluated on reef patches (Bora Bora, French Polynesia): (i) no-restored control, (ii) restored control, and two conditions with herbivorous invertebrates introduced (sea-urchins and mollusks) alongside restoration: (iii) one site with macroalgae removal and (iv) one without. Macroalgae cover and fish were monitored among the conditions over a 70-day period. Herbivorous invertebrates limited algae cover compared to control. However, no difference in fish assemblages was found in alpha diversity when comparing conditions over time. Changes in fish assemblages were observed in beta diversity, with statistically supported values for juveniles in the restored condition with herbivorous invertebrates present. Understanding the dynamics of ecological succession in so complex environments like coral reefs is essential for designing effective restoration strategies and safeguarding their health.